Altered expression of CD11b and CD62L after cross-linking of CD45 isoforms on human eosinophils

Background: Phosphotyrosine phosphatase CD45 is exclusively found on nucleated hematopoietic cells. CD45 is an essential component of signaling of mast cel degranulation and of lymphocyte activation, but little is known about its role in eosinophils. In the present study, we have determined the expression and function of CD45 isoforms on human eosinophils. Methods: Expression of CD45 isoforms on purified peripheral blood eosinophils was examined using indirect immunofluorescence and flow cytometry. Eosinophils were cultured with anti-CD45 isoform monoclonal antibodies (mAbs) for up to 24 h. Eosinophil activation was evaluated by measuring surface expression of CD11b or CD62L by flow cytometry. Results: Fresh eosinophils express CD45, CD45RB, CD45RO epitopes but not CD45RA. Incubation with anti-CD45 isoform mAb for 30 min did not alter the expression of either CD11b or CD62L on eosinophils. In contrast, the expression of CD11b was significantly enhanced after 24 h of incubation with mAbs against CD45, CD45RB, or CD45RO. In addition, the expression of CD62L was also significantly reduced with anti-CD45RB and with anti-CD45RO mAbs. Conclusions: Cross-linking of surface CD45 isoforms for 24 h significantly induced upregulation of CD11b expression and CD62L shedding, consistent with activation of eosinophils. Our data suggest that CD45 isoforms are functionally expressed on human eosinophils, and are capable of modulating eosinophil function and might participate in allergic inflammation.