Abstract

BackgroundAntenatal immune experience with Wuchereria bancrofti due to maternal filariasis may influence susceptibility to infection. We tested the hypothesis that filarial-specific T cell responses at birth that are indicative of in utero tolerance or sensitization affect the evolution of filarial-specific immunity and susceptibility to W. bancrofti infection during childhood

MethodsA birth-cohort study of 159 Kenyan newborns was performed. Cord blood and peripheral blood were obtained annually to age 7 years and were assayed for filarial infection and filarial antigen–driven interferon (IFN)–γ, interleukin (IL)–2, IL-5, and IL-13 production by lymphocytes

ResultsThere was a 12.9-fold (95% confidence interval [CI], 2.5–107.2-fold) and a 4.8-fold (95% CI, 1.7–12.9-fold) increased risk of infection for immune-tolerant newborns (maternal infection present during gestation, with no filarial antigen–driven cord blood T cell response [n=25]), compared with immune-sensitized (maternal infection present with cord blood T cell response [n=24]) and unexposed (maternal infection absent [n=110]) newborns. Cytokine responses developed at a later age in tolerant newborns, were characterized by impaired IFN-γ responses, and contrasted with those of filarial-sensitized newborns, who had sustained and elevated IL-5 and IL-13 responses to age 7 years

ConclusionPrenatal immune experience, as determined by whether in utero priming to filarial antigen occurs, is a major determinant of childhood susceptibility to W. bancrofti infection

More than 120 million residents of Africa, Latin America, Asia, and the Pacific region are infected with the lymphatic filarial parasites Wuchereria bancrofti and Brugia species, and >1 billion persons are at risk [1]. The distribution of infection and lymphatic disease attributable to these worms varies widely across and within populations in endemic areas, ranging from asymptomatic uninfected individuals to persons with light to heavy parasite burdens, with or without overt lymphatic pathological abnormalities [2]. These outcomes are not static; they are dynamic in that increasing age and cumulative exposure to mosquitoes bearing infective larvae correlate with higher infection burden and a propensity to develop lymphatic pathological abnormalities [3, 4]. Although host genetic polymorphism and bacterial superinfection may influence susceptibility to infection and disease [5–7], prenatal filarial-specific immune tolerance or sensitization associated with maternal infection during gestation and adaptive T cell cytokine responses appear to have a dominant effect. Cross-sectional surveys have shown that children whose mothers were putatively microfilaremic during gestation were more likely to be microfilaremic, compared with children whose mothers were amicrofilaremic during gestation [8–10]. Since childhood microfilaremic status was independent of paternal infection, these associations have been interpreted to indicate that the apparent increase in susceptibility was due to neonatal tolerance conferred by maternal filariasis [9, 10]. Indirect evidence supporting the importance of prenatal immune factors in determining the outcome of natural exposure to infective larvae derives from several observations. First, permanent residents of a filariasis-endemic area of Indonesia were found to have less-severe lymphatic pathological abnormalities, compared with recent migrants from nonendemic areas who were first exposed to mosquito-borne infective larvae as adults [11, 12]. Second, filarial-specific IgE and IgM, immunoglobulin isotypes that do not cross the placenta, have been detected in cord blood from infants born to mothers with filarial infection, suggesting in utero sensitization to filarial antigens [13–16]. Third, Steel et al. [17] compared filarial antigen–driven cytokine responses of Polynesian adolescents born to mothers who were putatively microfilaremic with those of Polynesian adolescents whose mothers were infection free. Although none of the study participants was infected (mass treatment with antifilarial drugs had been performed in the Cook Islands at least once since the time of the participants’ birth 17–19 years earlier), the 10 individuals born to infection-free mothers had stronger filarial-driven interleukin (IL)–2, IL-5, IL-10, and interferon (IFN)–γ responses than did the 11 individuals born to putatively microfilaremic mothers, suggesting that long-term immune tolerance is conferred by maternal filarial infection during gestation. The relationship between maternal filariasis and filarial-specific T cell immunity in newborns has, however, not been examined in any study. More importantly, it is not known whether or how maternally conferred immunity affects the evolution of parasite-specific T cell immunity and susceptibility to infection during childhood. We conducted a prospective cohort study of 159 Kenyan infants to address these gaps in knowledge

Subjects, Materials, and Methods

Prospective cohort studyThe institutional review boards of the Kenya Medical Research Institute and University Hospitals of Cleveland/Case Western Reserve University approved the prospective study of infants whose mothers attended the antenatal clinic and gave birth at Msambweni District Hospital in Coast Province, Kenya. The community-specific prevalence of W. bancrofti infection, on the basis of microfilaremia in the area, has a range of 9.2%–21.0% [10]. Inclusion criteria were uncomplicated singleton pregnancy, vaginal delivery, normal birth weight, permanent residence, and intent to remain in the area for the next 5 years. Exclusion criteria were complicated pregnancies (e.g., pre-ecampsia and poorly controlled diabetes), cesarean delivery, complicated vaginal delivery, and premature delivery (<36 weeks’ gestation). Systematic interventions against filariasis did not occur during the time when the study was conducted (1995–2002). In 2003, participants who were found to be infected were given a single dose of diethylcarbamazine (6 mg/kg of body weight) plus 400 mg of albendazole, under the auspices of a filariasis-elimination program initiated by the Kenya Ministry of Health

Diagnosis of filarial infectionThe filarial-infection status of pregnant women was determined before delivery, and the status of their infants was determined 1 time per year up to age 7 years on the basis of (1) IgG4 antibodies to a saline extract of B. malayi adult male and female worms (BmA) [14], (2) W. bancrofti–specific Og4C3 antigen in plasma (TropBioMed) [18], and (3) microscopic counting of microfilaremia after Nuclepore filtration of 1 mL of venous blood obtained between 2000 and 2400 h [19]. Maternal infection intensity was classified as light when BmA-specific IgG4 antibody alone was positive, moderate when BmA-specific IgG4 antibody plus Og4C3 antigen were positive, and heavy when all 3 tests were positive. Of note, pregnant women who were only BmA IgG4 positive could represent only continued exposure and may not have developed a fully patent filarial infection. Children were considered to be infected with W. bancrofti when Og4C3 levels exceeded 32 U/mL (the cutoff value recommended by the manufacturer) for 2 consecutive years. Infants who did not participate in the first follow-up examination at 1 year of age were excluded from analysis. Children who participated in the first-year visit and ⩾1 subsequent annual follow-up visit were included. IgG and IgE antibodies to B. malayi infective larvae were measured by ELISA and were used to evaluate exposure to infective larvae independent of infection status [20]

Diagnosis of nonfilarial infectionsThe presence of malaria parasites in venous blood and placental intervillous blood was determined by smear and real-time quantitative polymerase chain reaction of the gene encoding the small-subunit ribosomal RNA [21]. Childhood infection with intestinal helminths and urinary schistosomiasis was evaluated annually using the Kato method for fecal specimens and Nuclepore filtration of urine samples, respectively

Antigens and mitogensParasite antigens were saline extracts of BmA and microfilariae [15]. Protein antigen concentrations (5 or 10 μg/mL BmA and 1 μg/mL microfilarial antigen) were titrated to levels that failed to stimulate cytokine production by mononuclear cells isolated from cord blood from 10 healthy US newborns and peripheral blood from 8 healthy US adults. Phorbol 12-myristate 13-acetate (50 ng/mL; Calbiochem) and ionomycin (1 μg/mL; Calbiochem) were used as mitogens in parallel cultures. Mycobacterial purified protein derivative (PPD; Evans Medical) was used at a concentration of 10 μg/mL

Cytokine and antibody measurementsMononuclear cells were separated from heparin-anticoagulated cord blood from newborns and peripheral blood from children by density-gradient centrifugation on ficoll-hypaque, washed in RPMI 1640, and suspended to a final concentration of 2×106 cells/mL in RPMI 1640 supplemented with 10% fetal calf serum, 4 mmol/L l-glutamine, 25 mmol/L HEPES, and 80 μg/mL gentamicin (BioWhittaker). Antigens or mitogens were added to duplicate or triplicate cultures. Cultures with media alone served as controls. Cells were incubated at 37°C in 5% CO2, and supernatants were collected at 72 or 96 h for measurements of IL-2, IFN-γ, IL-5, and IL-13, which were performed as described elsewhere [15]. The limits of detection were 38 pg/mL for IL-2, 40 pg/mL for IFN-γ, 20 pg/mL for IL-5, and 32 pg/mL for IL-13. We analyzed filarial antigen–driven cytokine responses only when cord blood lymphocytes produced all 4 cytokines when stimulated with mitogen. Cord blood from 7 infants produced little or no cytokine production after mitogen stimulation, as a consequence of poor lymphocyte viability (n=4) or contamination of cultures (n=3) (e.g., spontaneous cytokine levels were high and obscured any mitogen or antigen-induced stimulation). None of these samples had detectable filarial antigen–induced cytokine production and, thus, could not be included in the analysis

Statistical analysisThe Mannc-Whitney U test was used for comparisons of cytokine responses by various groups of children. The χ2 test was used to compare the proportion of positive responders among the groups. A log-rank test was used to compare Kaplan-Meier survival curves for infection susceptibility according to maternal infection status alone and newborn filarial antigen–driven T cell responses combined with maternal infection status. The proportional hazard assumption was tested by assessing the log (−log)–estimated survival plotted against the log of time, where the assumption would be considered violated if plotted lines of exposure intersected. Without violation of this assumption, a Cox proportional hazard model was fit to compare the hazard across exposure status. Finally, the independence of survival time to hazard at time t in each exposure group was further tested by including time- and log of time–dependent exposure covariates, using the Wald statistic, where a significant time-dependent effect of exposure would be considered to violate the proportional hazard assumption. All analyses were performed using SAS (version 8.2; SAS Institute)

Results

An overview of the enrollment and follow-up of the participants is presented in figure 1. A total of 193 mother-newborn pairs were enrolled between 1995 and 1999; 83% of children in the birth cohort (n=159) remained in the study until follow-up ceased in 2002. Reasons for dropout and exclusion from analysis were death, emigration from the study area, and failure to attend at least 2 follow-up visits. The mean duration of follow-up was 4.3 years (range, 3.5–7.0 years)

Figure 1

Study design of newborn cohort followed for time to filarial infection

Figure 1

Study design of newborn cohort followed for time to filarial infection

Newborns were categorized according to the infection status of their mothers and whether cord blood filarial antigen–driven cytokine responses were detected (figure 1 and table 1). Of the 49 newborns whose mothers had indicators of active W. bancrofti infection, 24 had prima facie evidence of in utero sensitization—that is, cord blood lymphocyte IL-5, IL-13, IFN-γ, and/or IL-2 responses to filarial antigen. The remaining 25 newborns of W. bancrofti–infected mothers were categorized as tolerant—that is, cord blood lymphocyte antigen–driven cytokine responses were not detected despite coexisting maternal filarial infection. Cytokine responses by sensitized newborns indicated a mixed type 2 (IL-5 and/or IL-13)/type 1 (IFN-γ and/or IL-2) immunity that did not correlate with the intensity of maternal filarial infection (table 2)

Table 1

Characteristics of the newborn cohort, grouped according to maternal infection status and cord blood T cell cytokine response to filarial antigen

Table 1

Characteristics of the newborn cohort, grouped according to maternal infection status and cord blood T cell cytokine response to filarial antigen

Table 2

Filarial antigen–driven cytokine production by T cells of newborns with evidence of in utero sensitization to Wuchereria bancrofti

Table 2

Filarial antigen–driven cytokine production by T cells of newborns with evidence of in utero sensitization to Wuchereria bancrofti

We examined whether maternal infection intensity was associated with neonatal sensitization versus tolerance. Newborns categorized as tolerant had mothers with higher infection burdens, compared with those categorized as sensitized—that is, the proportion of microfilaremic mothers was greater in the former than in the latter group (13/25 vs. 7/24), whereas the opposite relationship existed when maternal BmA-specific IgG4 alone was the indicator of maternal infection (4/25 vs. 9/24). The 110 newborns whose mothers did not have active W. bancrofti infection—that is, those negative for BmA-specific IgG4 antibody, filarial antigememia, and microfilaremia—were categorized as unexposed and, therefore, neither sensitized nor tolerant. Cord blood lymphocytes from 106 (96%) of these donors did not produce any cytokine in response to BmA or microfilarial antigen. Three of the 4 newborns with filarial antigen–driven responses had mothers with schistosomiasis accompanied by cord blood lymphocyte responses to schistosome antigen. The 4 children whose lymphocytes responded to filarial antigens but who did not have mothers who were infected with or exposed to W. bancrofti were excluded from the category of “sensitized infants” in subsequent analyses. There were no significant differences among the 3 groups in maternal or childhood coinfections with malaria parasites, intestinal helminths, or schistosomes (table 1)

To assess the impact of neonatal immunity on the evolution of filarial T cell immunity during childhood, we evaluated cytokine responses to BmA and microfilarial antigen annually. The average duration of follow-up for the sensitized, tolerant, and unexposed groups was similar (figure 1). The number of children examined each year and the proportion in each group with T cell cytokine responses to filarial antigen are shown in table 3. Eighty-three percent of sensitized newborns (20/24) had a recall response to filarial antigen at age 1 year, compared with 12% (3/25) and 18% (20/110) in the tolerant and unexposed groups, respectively (P<.001). Filarial antigen–driven cytokine responses persisted in the sensitized group (i.e., responses were observed for 75%–89% of children from age 2 through 7). In contrast, lymphocyte reactivity to filarial antigen increased gradually with age in the other 2 groups (i.e., from 18%–66% at age 2–7 in the unexposed group). To examine the specificity of these responses for filarial antigen, we performed a similar analysis of PPD-driven IFN-γ production (all participants were given bacille Calmette-Guérin at birth, in accordance with the national policy in Kenya). The proportion of responders was similar in the 3 groups—in the sensitized group, at age 1, 2, 3, 4, 5, 6, and 7 years, 87%, 91%, 94%, 79%, 83%, 84%, and 92% of children, respectively, responded; in the tolerant group, at the same ages, 72%, 84%, 79%, 67%, 77%, 81%, and 73% of children, respectively, responded; and, in the unexposed group, at the same ages, 77%, 81%, 83%, 78%, 79%, 81%, and 86% of children, respectively, responded (P=.3)

Table 3

Filarial antigen–driven cytokine responses at ages 1 year to 7 years, in children classified at birth as sensitized, tolerant, or unexposed (no active maternal filarial infection during gestation)

Table 3

Filarial antigen–driven cytokine responses at ages 1 year to 7 years, in children classified at birth as sensitized, tolerant, or unexposed (no active maternal filarial infection during gestation)

To evaluate the impact of prenatal immunity on cytokine responses during childhood, we compared filarial antigen–driven IL-5 (type 2 cytokine) and IFN-γ (type 1 cytokine) responses in the 3 groups. IL-5 was dominant in the sensitized group, with an age-related increase in production of this cytokine (figure 2, upper panel). In contrast, the proportion of children with IL-5 responses in the tolerant and unexposed groups was lower at each year of follow-up. The pattern of filarial antigen–driven IFN-γ responses (figure 2, lower panel) was different than that of IL-5. First, production of this type 1 cytokine was minimal at ages 1 year and 2 years in all 3 groups. Second, there was a tendency for stronger responses beginning at age 3 years, especially among sensitized and unexposed newborns. Third, from age 3 through 7 years, tolerant newborns had significantly weaker IFN-γ responses than did the other 2 groups. The pattern of IL-13 and IL-2 production was similar to that of IL-5 and IFN-γ production, respectively. Microfilarial antigen–driven cytokine responses were similar to those elicited by BmA (data not shown)

Figure 2

Age-related filarial antigen–driven interleukin (IL)–5 and interferon (IFN)–γ production by peripheral blood mononuclear cells from children with evidence of in utero sensitization, tolerance, or neither (unexposed). Peak levels of IL-5 (upper panel) and IFN-γ (lower panel) are shown for 2×106 cells cultured with filarial antigen (BmA) at 48 or 96 h. Bars represent net geometric mean cytokine production (cell cultures with antigen minus media alone) ± SE. Asterisks indicate significant differences (P<.05, Mann-Whitney U test) between the sensitized group and either the tolerant group or the unexposed group (upper panel) and between the tolerant group and either the sensitized group or the unexposed group (lower panel)

Figure 2

Age-related filarial antigen–driven interleukin (IL)–5 and interferon (IFN)–γ production by peripheral blood mononuclear cells from children with evidence of in utero sensitization, tolerance, or neither (unexposed). Peak levels of IL-5 (upper panel) and IFN-γ (lower panel) are shown for 2×106 cells cultured with filarial antigen (BmA) at 48 or 96 h. Bars represent net geometric mean cytokine production (cell cultures with antigen minus media alone) ± SE. Asterisks indicate significant differences (P<.05, Mann-Whitney U test) between the sensitized group and either the tolerant group or the unexposed group (upper panel) and between the tolerant group and either the sensitized group or the unexposed group (lower panel)

To determine whether neonatal immunity associated with maternal filariasis influenced infection susceptibility, we compared the risk of acquiring W. bancrofti infection by offspring of infected versus uninfected mothers and of newborns categorized as sensitized, tolerant, or unexposed. The 49 children whose mothers had filariasis included a higher proportion who became infected between ages 1 year and 7 years, compared with the 110 children of mothers without filariasis, but these values were not significantly different (χ2=2.55 [1 df]; P=.10; hazard ratio for children of infected vs. uninfected women, 0.941 [95% confidence interval {CI}, 0.495–1.813]) (figure 3, upper panel). Newborns with evidence of filarial-specific immune tolerance had a 12.9-fold greater risk of infection, compared with those with evidence of sensitization (χ2=9.43 [1 df]; P<.001; 95% CI, 2.5–107.2-fold). The tolerant group was also 4.8 times more likely to become infected, compared with newborns born to uninfected women (χ2=11.88 [1 df]; P<.001; 95% CI, 1.7–12.9-fold). There was no difference in the risk of infection between the sensitized and the nonsensitized unexposed groups (χ2=0.81 [1 df]; P=.33) (figure 3, lower panel)

Figure 3

Kaplan-Meier time-to-infection survival curves for children of filarial-infected mothers (solid line) vs. children of uninfected mothers (dashed line) (A) and children with evidence of in utero sensitization (dotted line) in utero tolerance (solid line) or neither (unexposed; dashed line) (B). Time to infection for the 2 groups in panel A did not differ (χ2=2.55 [1 df]; hazard ratio, 0.941 [95% confidence interval, 0.495–1.813]). The difference in time to infection among the 3 groups in panel B was significant (P<.0001), as was the comparison between children with evidence of in utero sensitization and those with in utero tolerance (P<.001) and between children with in utero tolerance and those who were unexposed (P<.001). There was not a significant difference between children with evidence of in utero sensitization and those who were unexposed in utero (P>.10)

Figure 3

Kaplan-Meier time-to-infection survival curves for children of filarial-infected mothers (solid line) vs. children of uninfected mothers (dashed line) (A) and children with evidence of in utero sensitization (dotted line) in utero tolerance (solid line) or neither (unexposed; dashed line) (B). Time to infection for the 2 groups in panel A did not differ (χ2=2.55 [1 df]; hazard ratio, 0.941 [95% confidence interval, 0.495–1.813]). The difference in time to infection among the 3 groups in panel B was significant (P<.0001), as was the comparison between children with evidence of in utero sensitization and those with in utero tolerance (P<.001) and between children with in utero tolerance and those who were unexposed (P<.001). There was not a significant difference between children with evidence of in utero sensitization and those who were unexposed in utero (P>.10)

To examine whether differences in infection susceptibility were related to exposure to mosquito-borne infective larvae, we measured IgG and IgE antibodies to infective larvae annually [20]. A positive response indicating exposure to mosquito-borne filarial larvae was scored when the ELISA optical density was greater than the mean plus 3 SDs of control serum samples from children residing in the Turkana region in Kenya. Intestinal helminth infections and echinococcosis are endemic, but lymphatic filariasis is absent, in Turkana. No differences among the groups were observed. The proportions of children who were IgG and/or IgE antibody positive at ages 1 year through 7 years were 8%, 10%, 14%, 25%, 45%, 47%, and 62%, respectively, in the tolerant group; 4%, 10%, 14%, 25%, 33%, 38%, and 44%, respectively, in the sensitized group; and 3%, 5%, 10%, 13%, 19%, 28%, and 41%, respectively, in the unexposed group (P>.1). Clustering of infection-positive children according to village or household of residence was not observed (table 1)

Discussion

Our results show that in utero acquisition of T cell immunity to filarial antigens has a major impact on susceptibility to infection with W. bancrofti during childhood. Prenatal filarial-specific immune tolerance as a consequence of active maternal filariasis increased the risk of infection during the first 7 years after birth 12.9-fold, compared with that in newborns with evidence of in utero sensitization, and 4.8-fold, compared with that in newborns who were neither tolerant nor sensitized, because their mothers lacked active W. bancrofti infection. Conversely, newborns with prenatal immune sensitization marked by filarial-responsive T cells at birth maintained this immunity throughout childhood and had reduced susceptibility to infection, suggesting that prenatal lymphocyte priming confers partial protection against infective larvae or the establishment of adult worms

Susceptibility to filarial infection may be affected by factors in addition to the antenatal immune mechanisms examined here. First, heterogeneity in exposure to infective larvae could account for differences in infection outcome. It is not possible to directly measure the cumulative exposure of an individual to mosquitoes bearing infective larvae. We used the presence of IgE and IgG antibodies to infective larvae as a surrogate measure of exposure. The proportion of children in each group who developed such antibody responses over time was similar. Second, coinfection with malaria or intestinal worms could induce bias in T cell cytokine responses and thereby affect susceptibility to W. bancrofti infection. Malaria, geohelminth, and schistosome infection rates were similar among the 3 groups. Third, genetic differences may affect susceptibility to lymphatic filariasis [22–24], but, to our knowledge, there are no data demonstrating the contribution of specific genes to infection susceptibility in humans

The differences in cellular immune responses to filarial antigens observed here suggest that several mechanisms may contribute to the control of susceptibility to infection. With respect to children who were relatively resistant to infection, prenatal priming generated a population of filarial-specific lymphocytes that persisted from birth through age 7 years. The dominant cytokine was IL-5 (IL-13 followed a similar pattern but was detected in a lower proportion of participants). These children produced little filarial antigen–driven IFN-γ and IL-2, even though their T cells at birth produced both type 2 (IL-5 and/or IL-13) and type 1 (IFN-γ and/or IL-2) cytokines. This result suggests that filarial-specific lymphocytes with a predominant type 2 phenotype are more likely to survive into childhood. This phenomenon has also been observed following fetal exposure to allergens [25]. The persistence of filarial antigen–driven IL-5 among putatively resistant children implicates a protective role of this cytokine. This conclusion is supported by observations in mouse models of filariasis. Mice deficient in IL-5 were more susceptible to filarial infection than were wild-type controls [26, 27], and IL-5–transgenic mice were more resistant than were normal mice [28]

The lack of filarial antigen–specific responses in some children of filarial-infected women represents either immune tolerance or a lack of fetal exposure to filarial antigens. We believe that immune tolerance is the most likely explanation, because mothers of tolerant newborns had higher infection burdens than did mothers whose newborns had evidence of lymphocyte priming. Additionally, the proportion of children in the tolerant group with recall responses and the amount of IFN-γ produced were less than those in the other groups, indicating a reduced frequency of antigen-reactive cells that may arise from clonal deletion or T cell anergy [29]. Alternatively, regulatory T cells producing IL-10 and tumor growth factor–β may be expanded [30–32]. In either case, impaired IFN-γ responses correlated with increased susceptibility to infection during childhood (figure 2). Strong filarial antigen–driven IFN-γ production is characteristic of putatively immune, “endemic normal” subjects and has been suggested to be linked with protection against filariasis [33, 34]

Humoral immunity to infective-stage larvae has been implicated in protection in animal models of filarias [35, 36]. Preliminary data indicate that children with evidence of in utero sensitization have increased antilarval IgE antibodies, compared with IgG4 antibodies, whereas the reverse relationship exists in children who become tolerant in utero. A similar relationship between larval-specific IgE and IgG4 has been suggested to correlate with protection against human lymphatic filariasis [37]. Elevated antiparasite IgE:IgG4 ratios have been associated with acquired resistance in human schistosomiasis [38, 39]

The mechanisms by which the fetus is exposed to filarial antigen in utero and the factors determining whether such exposure results in priming or tolerance remain poorly understood. Microfilariae rarely cross the placenta [40, 41], and one report suggested that filarial antigen is found in 10% of cord blood samples from newborns born to mothers with filariasis [42]. However, we have not detected filarial antigen in cord blood, using the Og4C3 or other antigen-capture assays [43]. Factors altering the integrity of the placenta (such as damage resulting from placental malaria, which is coendemic in the area) may affect the time and efficiency of passage of filarial antigen from the maternal to the fetal circulation during gestation [44]

A practical implication of the present study relates to the potential impact that mass treatment programs aimed at eliminating transmission of W. bancrofti [45] may have on prenatal immune priming and tolerance. On the one hand, reduction of filarial infection burdens in women of childbearing age may diminish prenatal immune tolerance and, thus, decrease the risk of infection during childhood. On the other hand, the risk of developing lymphatic pathological abnormalities might increase if transmission is not stopped and if exposure to infective larvae is delayed to later in life. With the recent commencement of a mass treatment program in Kenya, continued monitoring of both the current and a newly established birth cohort may help to address some of these questions

Acknowledgments

We appreciate the assistance of Adams Omollo, Kephar Otieno, and Elton K. Mzungu, for technical help, and of Grace Watutu, for data entry. We are grateful to the maternity nurses and the women and children in Kenya who participated in this study

References

1
Michael
E
Bundy
DA
Grenfell
BT
Re-assessing the global prevalence and distribution of lymphatic filariasis
Parasitology
 , 
1996
, vol. 
112(Pt 4)
 (pg. 
409
-
28
)
2
Ottesen
EA
The Wellcome Trust Lecture. Infection and disease in lymphatic filariasis: an immunological perspective
Parasitology
 , 
1992
, vol. 
104(Suppl)
 (pg. 
S71
-
9
)
3
Kazura
JW
Bockarie
M
Alexander
N
, et al.  . 
Transmission intensity and its relationship to infection and disease due to Wuchereria bancrofti in Papua New Guinea
J Infect Dis
 , 
1997
, vol. 
176
 (pg. 
242
-
6
)
4
Tobian
AA
Tarongka
N
Baisor
M
Bockarie
M
Kazura
JW
King
CL
Sensitivity and specificity of ultrasound detection and risk factors for filarial-associated hydroceles
Am J Trop Med Hyg
 , 
2003
, vol. 
68
 (pg. 
638
-
42
)
5
Choi
EH
Nutman
TB
Chanock
SJ
Genetic variation in immune function and susceptibility to human filariasis
Expert Rev Mol Diagn
 , 
2003
, vol. 
3
 (pg. 
367
-
74
)
6
Dreyer
G
Noroes
J
Figueredo-Silva
J
Piessens
WF
Pathogenesis of lymphatic disease in bancroftian filariasis: a clinical perspective
Parasitol Today
 , 
2000
, vol. 
16
 (pg. 
544
-
8
)
7
Nutman
TB
Kumaraswami
V
Regulation of the immune response in lymphatic filariasis: perspectives on acute and chronic infection with Wuchereria bancrofti in South India
Parasite Immunol
 , 
2001
, vol. 
23
 (pg. 
389
-
99
)
8
Alexander
ND
Kazura
JW
Bockarie
MJ
, et al.  . 
Parental infection confounded with local infection intensity as risk factors for childhood microfilaraemia in bancroftian filariasis
Trans R Soc Trop Med Hyg
 , 
1998
, vol. 
92
 (pg. 
23
-
4
)
9
Lammie
PJ
Hitch
WL
Walker Allen
EM
Hightower
W
Eberhard
ML
Maternal filarial infection as risk factor for infection in children
Lancet
 , 
1991
, vol. 
337
 (pg. 
1005
-
6
)
10
Malhotra
I
Ouma
JH
Wamachi
A
, et al.  . 
Influence of maternal filariasis on childhood infection and immunity to Wuchereria bancrofti in Kenya
Infect Immun
 , 
2003
, vol. 
71
 (pg. 
5231
-
7
)
11
Partono
F
Pribadi
PW
Soewarta
A
Epidemiological and clinical features of Brugia timori in a newly established village: Karakuak, West Flores, Indonesia
Am J Trop Med Hyg
 , 
1978
, vol. 
27
 (pg. 
910
-
5
)
12
Partono
F
Purnomo. Clinical features of timorian filariasis among immigrants to an endemic area in West Flores, Indonesia
Southeast Asian J Trop Med Public Health
 , 
1978
, vol. 
9
 (pg. 
338
-
43
)
13
Dissanayake
S
de Silva
LV
Ismail
MM
IgM antibody to filarial antigens in human cord blood: possibility of transplacental infection
Trans R Soc Trop Med Hyg
 , 
1980
, vol. 
74
 (pg. 
542
-
4
)
14
King
CL
Malhotra
I
Mungai
P
, et al.  . 
B cell sensitization to helminthic infection develops in utero in humans
J Immunol
 , 
1998
, vol. 
160
 (pg. 
3578
-
84
)
15
Malhotra
I
Ouma
J
Wamachi
A
, et al.  . 
In utero exposure to helminth and mycobacterial antigens generates cytokine responses similar to that observed in adults
J Clin Invest
 , 
1997
, vol. 
99
 (pg. 
1759
-
66
)
16
Weil
GJ
Hussain
R
Kumaraswami
V
Tripathy
SP
Phillips
KS
Ottesen
EA
Prenatal allergic sensitization to helminth antigens in offspring of parasite-infected mothers
J Clin Invest
 , 
1983
, vol. 
71
 (pg. 
1124
-
9
)
17
Steel
C
Guinea
A
McCarthy
JS
Ottesen
EA
Long-term effect of prenatal exposure to maternal microfilaraemia on immune responsiveness to filarial parasite antigens
Lancet
 , 
1994
, vol. 
343
 (pg. 
890
-
3
)
18
More
SJ
Copeman
DB
A highly specific and sensitive monoclonal antibody-based ELISA for the detection of circulating antigen in bancroftian filariasis
Trop Med Parasitol
 , 
1990
, vol. 
41
 (pg. 
403
-
6
)
19
Eberhard
ML
Lammie
PJ
Laboratory diagnosis of filariasis
Clin Lab Med
 , 
1991
, vol. 
11
 (pg. 
977
-
1010
)
20
Helmy
H
Weil
GJ
Faris
R
, et al.  . 
Human antibody responses to Wuchereria bancroftiinfective larvae
Parasite Immunol
 , 
2000
, vol. 
22
 (pg. 
89
-
96
)
21
Malhotra
I
Mungai
P
Muchiri
E
, et al.  . 
Distinct Th1- and Th2-type prenatal cytokine responses to Plasmodium falciparumerythrocyte invasion ligands
Infect Immun
 , 
2005
, vol. 
73
 (pg. 
3462
-
70
)
22
Terhell
AJ
Houwing-Duistermaat
JJ
Ruiterman
Y
Haarbrink
M
Abadi
K
Yazdanbakhsh
M
Clustering of Brugia malayiinfection in a community in South-Sulawesi, Indonesia
Parasitology
 , 
2000
, vol. 
120
 (pg. 
23
-
9
)
23
Romia
SA
el-Ganayni
GA
Makhlouf
LM
Handousa
AE
HLA antigens and blood groups in bancroftian filariasis
J Egypt Soc Parasitol
 , 
1988
, vol. 
18
 (pg. 
211
-
20
)
24
Choi
EH
Zimmerman
PA
Foster
CB
, et al.  . 
Genetic polymorphisms in molecules of innate immunity and susceptibility to infection with Wuchereria bancroftiin South India
Genes Immun
 , 
2001
, vol. 
2
 (pg. 
248
-
53
)
25
Prescott
SL
Macaubas
C
Smallacombe
T
Holt
BJ
Sly
PD
Holt
PG
Development of allergen-specific T-cell memory in atopic and normal children
Lancet
 , 
1999
, vol. 
353
 (pg. 
196
-
200
)
26
Le Goff
L
Loke
P
Ali
HF
Taylor
DW
Allen
JE
Interleukin-5 is essential for vaccine-mediated immunity but not innate resistance to a filarial parasite
Infect Immun
 , 
2000
, vol. 
68
 (pg. 
2513
-
7
)
27
Volkmann
L
Bain
O
Saeftel
M
, et al.  . 
Murine filariasis: interleukin 4 and interleukin 5 lead to containment of different worm developmental stages
Med Microbiol Immunol
 , 
2003
, vol. 
192
 (pg. 
23
-
31
)
28
Martin
C
Al-Qaoud
KM
Ungeheuer
MN
, et al.  . 
IL-5 is essential for vaccine-induced protection and for resolution of primary infection in murine filariasis
Med Microbiol Immunol
 , 
2000
, vol. 
189
 (pg. 
67
-
74
)
29
King
CL
Kumaraswami
V
Poindexter
RW
, et al.  . 
Immunologic tolerance in lymphatic filariasis: diminished parasite-specific T and B lymphocyte precursor frequency in the microfilaremic state
J Clin Invest
 , 
1992
, vol. 
89
 (pg. 
1403
-
10
)
30
Babu
S
Kumaraswami
V
Nutman
TB
Transcriptional control of impaired Th1 responses in patent lymphatic filariasis by T-box expressed in T cells and suppressor of cytokine signaling genes
Infect Immun
 , 
2005
, vol. 
73
 (pg. 
3394
-
401
)
31
Gillan
V
Devaney
E
Regulatory T cells modulate Th2 responses induced by Brugia pahangi third-stage larvae
Infect Immun
 , 
2005
, vol. 
73
 (pg. 
4034
-
42
)
32
Taylor
MD
LeGoff
L
Harris
A
Malone
E
Allen
JE
Maizels
RM
Removal of regulatory T cell activity reverses hyporesponsiveness and leads to filarial parasite clearance in vivo
J Immunol
 , 
2005
, vol. 
174
 (pg. 
4924
-
33
)
33
Dimock
KA
Eberhard
ML
Lammie
PJ
Th1-like antifilarial immune responses predominate in antigen-negative persons
Infect Immun
 , 
1996
, vol. 
64
 (pg. 
2962
-
7
)
34
Ravindran
B
Satapathy
AK
Sahoo
PK
Mohanty
MC
Protective immunity in human lymphatic filariasis: problems and prospects
Med Microbiol Immunol
 , 
2003
, vol. 
192
 (pg. 
41
-
6
)
35
Paciorkowski
N
Shultz
LD
Rajan
TV
Primed peritoneal B lymphocytes are sufficient to transfer protection against Brugia pahangiinfection in mice
Infect Immun
 , 
2003
, vol. 
71
 (pg. 
1370
-
8
)
36
Partono
F
Oemijati
S
The association of clinical filariasis and Wuchereria bancroftiinfections in Jakarta
Southeast Asian J Trop Med Public Health
 , 
1978
, vol. 
9
 (pg. 
260
-
3
)
37
Nielsen
NO
Bloch
P
Simonsen PE. Lymphatic filariasis-specific immune responses in relation to lymphoedema grade and infection status
II
Humoral responses
Trans R Soc Trop Med Hyg
 , 
2002
, vol. 
96
 (pg. 
453
-
8
)
38
Demeure
CE
Rihet
P
Abel
L
Ouattara
M
Bourgois
A
Dessein
AJ
Resistance to Schistosoma mansoni in humans: influence of the IgE/IgG4 balance and IgG2 in immunity to reinfection after chemotherapy
J Infect Dis
 , 
1993
, vol. 
168
 (pg. 
1000
-
8
)
39
Hagan
P
Blumenthal
UJ
Dunn
D
Simpson
AJ
Wilkins
HA
Human IgE, IgG4 and resistance to reinfection with Schistosoma haematobium
Nature
 , 
1991
, vol. 
349
 (pg. 
243
-
5
)
40
Campello
TR
Ferreira
RS
Pires
ML
, et al.  . 
A study of placentas from Wuchereria bancroftimicrofilaraemic and amicrofilaraemic mothers
J Trop Med Hyg
 , 
1993
, vol. 
96
 (pg. 
251
-
5
)
41
Eberhard
ML
Hitch
WL
McNeeley
DF
Lammie
PJ
Transplacental transmission of Wuchereria bancroftiin Haitian women
J Parasitol
 , 
1993
, vol. 
79
 (pg. 
62
-
6
)
42
Hitch
WL
Eberhard
ML
Lammie
PJ
Investigation of the influence of maternal infection with Wuchereria bancrofti on the humoral and cellular responses of neonates to filarial antigens
Ann Trop Med Parasitol
 , 
1997
, vol. 
91
 (pg. 
461
-
9
)
43
Ramzy
RM
Gad
AM
Faris
R
Weil
GJ
Evaluation of a monoclonal-antibody based antigen assay for diagnosis of Wuchereria bancrofti infection in Egypt
Am J Trop Med Hyg
 , 
1991
, vol. 
44
 (pg. 
691
-
5
)
44
Crocker
IP
Tanner
OM
Myers
JE
Bulmer
JN
Walraven
G
Baker
PN
Syncytiotrophoblast degradation and the pathophysiology of the malaria-infected placenta
Placenta
 , 
2004
, vol. 
25
 (pg. 
273
-
82
)
45
Ottesen
EA
The global programme to eliminate lymphatic filariasis
Trop Med Int Health
 , 
2000
, vol. 
5
 (pg. 
591
-
4
)
Potential conflicts of interest: none reported
Presented in part: annual meeting of the International Centers for Tropical Disease Research, Bethesda, Maryland, 14 May 2004
Financial support: National Institutes of Health, US Public Health Service (grants AI36219 and AI33061)