Various Authentic Chemoattractants Mediating Leukocyte Adherence Inhibition

Abstract

This study resulted from the finding that cancer extract-induced leukocyte adherence inhibition (LAI) depends on release of arachidonic acid metabolites of which leukotriene B₄ (LTB₄) is a chemoattractant. Leukotrienes, the chemotactic fragment of the fifth component of complement (C5a des arg), N-formyl-l-methionyl-l-leucyl-l-phenylalanine (FMLP), platelet-activating factor (PAF), and phorbol myristate acetate (PMA) increased the nonadherence of human leukocytes to glass with bell-shaped dose-response curves. For maximum nonadherence, the optimum concentration was about 2×10⁻¹¹M LTB₄, 10⁻⁹M C5a des arg, 2×10⁻⁸M FMLP, 2×10⁻⁹M PAF, and 2×10⁻⁸M PMA. Of the adherent leukocytes, 29% became nonadherent. Higher concentrations of leukotriene E₄, FMLP, PAF, and PMA induced leukocyte hyperadhesiveness. Chemoattractant-induced LAI was antagonized by inhibitors of glycolysis, oxidative metabolism, electron transport, microfilaments, and microtubules, whereas the same concentration of inhibitors did not alter the adherence of leukocytes to glass in control tubes. T-cells, neutrophils, and mononuclear cells showed LAI to LTB₄, C5a des arg, and FMLP. Moreover, no additive effect was observed when leukocytes exposed to a first chemoattractant at its optimum concentration were exposed to a second. A competitive inhibitor of leukotriene slow-reacting substance of anaphylaxis, FPL 55712, blocked in a dose-response fashion LTB₄-, C5a des arg-, and FMLP-triggered LAI. Eicosatetraenoic acid and nordihydroguaiaretic acid, cyclooxygenase-lipoxygenase pathway inhibitors, also markedly antagonized LTB₄-, C5a des arg-, and FMLP-triggered LAI. Indomethacin (10⁻⁵M), piroxicam (10⁻⁶M), and aspirin, cyclooxygenase antagonists, negated LTB₄-, C5a des arg-, and FMLP-induced LAI. Prostaglandins E₂, E₁, and F₂ and prostacyclin did not trigger LAI. However, selective thromboxane synthetase antagonists completely negated chemoattractant-triggered LAI. Our studies indicated that chemoattractants stimulated leukocytes to produce thromboxanes, which increased leukocyte nonadherence.