Role of secretory IgA, secretory component, and eosinophils in mucosal inflammation.

Eosinophils and their products are important in the pathophysiology of allergic inflammation in mucosal tissues. Secretory component (SC) bound to IgA mediates transepithelial transport of IgA. As another biological activity of SC, we have reported that secretory IgA (sIgA) and SC preferentially activate human eosinophils. When eosinophils were stimulated with immobilized sIgA, degranulation and superoxide production were greater than when stimulated with serum IgA. In contrast, neutrophils responded similarly to sIgA and serum IgA. Superoxide production by eosinophils stimulated with cytokines was enhanced synergistically by immobilized SC, while SC showed no effect on neutrophil activation. Eosinophil superoxide production stimulated with sIgA was abolished by anti-CD18 mAb, suggesting that beta2 integrins might be crucial for this reaction. There are several reports that SC and sIgA may play important roles in regulating eosinophil functions in vivo in diseases associated with mucosal eosinophilia and in various allergic diseases. It is speculated that eosinophils in the mucosa are activated by SC or sIgA, and that subsequent degranulation and superoxide production are induced.