Variation among populations in the immune protein composition of mother’s milk reflects subsistence pattern

Abstract Lay Summary Adaptive immune proteins in mothers’ milk are more variable than innate immune proteins across populations and subsistence strategies. These results suggest that the immune defenses in milk are shaped by a mother’s environment throughout her life. Background and objectives Mother’s milk contains immune proteins that play critical roles in protecting the infant from infection and priming the infant’s developing immune system during early life. The composition of these molecules in milk, particularly the acquired immune proteins, is thought to reflect a mother’s immunological exposures throughout her life. In this study, we examine the composition of innate and acquired immune proteins in milk across seven populations with diverse disease and cultural ecologies. Methodology Milk samples (n = 164) were collected in Argentina, Bolivia, Nepal, Namibia, Philippines, Poland and the USA. Populations were classified as having one of four subsistence patterns: urban-industrialism, rural-shop, horticulturalist-forager or agro-pastoralism. Milk innate (lactalbumin, lactoferrin and lysozyme) and acquired (Secretory IgA, IgG and IgM) protein concentrations were determined using triple-quadrupole mass spectrometry. Results Both innate and acquired immune protein composition in milk varied among populations, though the acquired immune protein composition of milk differed more among populations. Populations living in closer geographic proximity or having similar subsistence strategies (e.g. agro-pastoralists from Nepal and Namibia) had more similar milk immune protein compositions. Agro-pastoralists had different milk innate immune protein composition from horticulturalist-foragers and urban-industrialists. Acquired immune protein composition differed among all subsistence strategies except horticulturist-foragers and rural-shop. Conclusions and implications Our results reveal fundamental variation in milk composition that has not been previously explored in human milk research. Further study is needed to understand what specific aspects of the local environment influence milk composition and the effects this variation may have on infant health outcomes.

gather opportunistically, most households primarily depend on wages from men's labor or government subsidies [58]. Women's activities typically include household chores, children caretaking, and basket weaving. Some women also participate in the market economy, either through employment such as cooks and teachers' assistants or by selling handicrafts [137].
The provincial government offers free healthcare at local clinics, including pre-and postnatal care programs. Nearly all infants are born at hospitals, however infant and child mortality rates are high and largely due to preventable causes [58]. Infant illnesses, such as respiratory and diarrheal infections, have previously been reported to be common among this group of participants [5]. Tuberculosis, urinary infections, and gastrointestinal infectious are common among adults in this community [58]. Obesity rates among Qom adults are also increasing as a result of dietary and lifestyle changes, and nearly half of adult women are overweight or obese [138].
Ethical approval for work with the Qom was granted by the University of Pennsylvania Institutional Review Board (#811200).

PHILIPPINES: Filipino samples were collected in collaboration with the Cebu Longitudinal
Health and Nutrition Survey (CLHNS) during September 2007 to March 2008. The CLHNS is an ongoing birth cohort study of individuals in 33 communities within the Cebu metropolitan area [139,140]. Metropolitan Cebu is the second-largest metropolitan area in the Philippines, with a total population of around 2 million [140]. Half of the participants involved in this study were recruited from urban areas where residents primarily engaged in wage labor, and half from surrounding agrarian communities that practiced small-scale farming. As there was variation in the urbanicity of this sample, households varied somewhat among urban and rural communities.
While concrete or bamboo floors are common in both urban and rural areas, indoor plumbing is not found in rural homes but is sometimes present in urban homes. Participants also varied in their access to small neighborhood convenience stores and larger grocery stores [141]. However, both groups had access to a variety of commercially produced foods as well as local produce, eggs, and fish. It is not uncommon for women to own or work in small neighborhood convenience stores, which often have many snack foods [142].
As in many developing countries, increasing household incomes and ownership of consumer goods in this population have been associated with increasing rates of overweight and obesity [142]. However, infectious diseases continue to be a leading cause of mortality in Southeast Asia, including the Philippines [143]. Respiratory infections are the third leading cause of death for both adults and children under five in the Philippines [144].
Ethical approval for work with the Cebu was granted by Northwestern University and the University of San Carlos, Philippines (both #STU00001299). wheat, rye, potatoes, vegetables, and fruits such as raspberries and plums [146]. When conducted, women participate in the highly seasonal and labor-intensive agricultural work [50].
Most households also keep a cow or chickens [146]. Food that is not grown or produced by the households is typically purchased from small local shops.
Nearly all Polish citizens have compulsory health insurance through government programs [147]. Modern medical care at the Mogielica Human Ecology Study Site is available at several local clinics and a small hospital that is accessible by local bus routes. Since 1989, country-level health indicators such as life expectancy and infant mortality rates have improved but are still lower and higher, respectively, than many other European countries [148]. Chronic conditions such as cardiovascular disease, respiratory diseases, and cancers among the most common causes of death in Poland [147].
Ethical approval for work in Poland was granted by the Harvard University Committee on the Use of Human Subjects (#21979, #IRB13-0900). . In addition to hunting and fishing, the Tsimane grow plantains, rice, corn/maize, and manioc/cassava using slash-and-burn horticulture [36]. They also have small livestock, such as pigs and chickens [148]. Most Tsimane obtain water from rivers and streams, and rarely boil water before drinking it. The average adult diet is comprised of 74% plant and 26% animal foods, with market foods (pasta, bread, beef jerky, etc.) comprising < 4% of total dietary energy [69].

HORTICULTURALIST-FORAGERS
The Tsimane have minimal access to regular health care or medications [149]. Hygienic conditions are generally poor and helminthic, protozoal, fungal, and other infections are common throughout life [150]. The average life expectancy is 54 years, and approximately half of all deaths since 1950 are due to infectious diseases [36,149]. Stunting rates are high, likely due to poor dietary quality and high infectious disease burden, but Tsimane are generally are not malnourished [148]. . Some foraging still occurs, particularly during drought years, mainly for palm nuts and honey. Women have also recently begun growing maize and millet in seasonal gardens [118,152].
Access to modern healthcare is limited. There is one small clinic a day's walk from the study area [118]. However, routine medical care is not common and many pastoralists in the area do not know their exact age [153]. Most women continue to give birth at home with the assistance of kin or midwives [118]. Contraceptive knowledge is scarce, so this is still considered a "natural fertility" population [52]. Similar to other pastoralist populations, infant mortality rates have been estimated to be high, between 12 and 48% of all births [118]. The Himba have high levels of STI infections, and infections are more common in women than men [153].
Ethical approval for work with the Himba was granted by the University of California Los Angeles IRB (IRB#13-000881). Ethical approval for work with the Nubri was granted by Washington University in St.