Expression of CD28 and CD86 by human eosinophils and role in the secretionof type 1 cytokines (Interleukin 2 and interferon gamma): Inhibition by immunoglobulin A complexes

Eosinophils are the source of various immunoregulatory cytokines, but the m embrane molecules involved in their secretion have not been clearly identif ied. Here we show that peripheral blood eosinophils from hypereosinophilic patients could express membrane CD86 but not CD80. The T cell costimulatory molecule CD28 is also detected on the eosinophil surface. CD28 ligation bu t not CD86 ligation resulted in interleukin (IL)-2 and interferon (IFN)-gam ma secretion by eosinophils, whereas IL-4, IL-5, and IL-10 were not detecte d. In contrast to T cells requiring two signals for effective stimulation, CD28 ligation alone was sufficient for optimal eosinophil activation. Eosin ophil-derived IL-2 and IFN-gamma were biologically active, as supernatants from anti-CD28-treated cells were able to induce CTLL-2 proliferation and m ajor histocompatibility complex class II expression on the colon carcinoma cell line Cole 205, respectively. Addition of secretory immunoglobulin (Ig) A-anti-IgA complexes, which could induce the release of IL-10, very signifi cantly inhibited both CD28-mediated IL2 and IFN-gamma release. These result s suggest that the release of type 1 (IFN-gamma and IL-2) versus type 2 cyt okines by eosinophils is not only differential but also dependent on cross- regulatory signals. They confirm that through activation of costimulatory m olecules, eosinophils could function as an immunoregulatory cell involved i n the release of both type 1 and type 2 cytokines.