CHARACTERIZATION OF EOSINOPHIL HOMOTYPIC AGGREGATION

Guinea pig peritoneal eosinophils stimulated by platelet-activating fa ctor (PAF), leukotriene B-4 (LTB(4)), and human recombinant C5a (C5a) undergo a rapid concentration-dependent and partially reversible homot ypic aggregation as assessed by changes in light transmission. The pho rbol ester phorbol myristate acetate similarly induces a concentration -dependent aggregation, which is, however, slower in onset, takes long er to reach maximal aggregation, and is irreversible. In addition, we confirmed, using light microscopy, that these agonist-induced changes in light transmission do indeed represent true homotypic aggregation. We further characterized the aggregation response and showed that ther e is homologous but little heterologous desensitization when PAF and L TB(4) are used as stimuli. A requirement for both Ca2+ and Mg2+ for fu ll manifestation of agonist-induced aggregation was observed. LTB(4)- and PAF-induced superoxide anion generation is enhanced by the diacylg lycerol kinase inhibitor R59022, whereas aggregation induced by LTB(4) , but not PAF, is augmented. Lastly, we show that eosinophil aggregati on is partially dependent on the adhesion glycoprotein CD18. In summar y, therefore, we believe that eosinophil aggregation provides a useful and reliable measure of eosinophil activation.