INTERACTION WITH SECRETORY COMPONENT STIMULATES EFFECTOR FUNCTIONS OFHUMAN EOSINOPHILS BUT NOT OF NEUTROPHILS

Eosinophils and their products are important in the pathophysiology of allergic inflammation in mucosal tissues. Secretory component bound t o IgA mediates transepithelial transport of IgA and confers increased stability on the resultant secretory IgA; however, the effect of secre tory component on the biologic activity of IgA is unknown. Here, we re port that secretory IgG and secretory component preferentially activat e human eosinophils. When eosinophils were stimulated with immobilized secretory IgA, degranulation and superoxide production were two- to t hreefold greater than when stimulated with serum IgA, In contrast, neu trophils responded similarly to secretory IgA and serum IgA, Flow cyto metric analysis showed that eosinophils bound to purified secretory co mponent. The binding of I-125-Iabeled secretory component was inhibite d by unlabeled secretory component or secretory IgA hut not by serum I gA, Superoxide production by eosinophils stimulated with cytokines or IgG was enhanced synergistically by immobilized secretory component; s ecretory component showed no effect on neutrophil activation. Finally, anti-CD18 mAb abolished eosinophil superoxide production stimulated w ith secretory IgA or secretory component but not with serum IgA, sugge sting a crucial role for beta(2) integrins in eosinophil interactions with secretory IgA or secretory component. Thus, secretory component p lays important roles in activating eosinophil functions but not neutro phil functions. This preferential interaction between secretory compon ent and eosinophils may provide a novel mechanism to regulate mucosal tissue inflammation.