Inhibition of ongoing immunoglobulin production by eosinophil cationic protein

The effect of eosinophil cationic protein (ECP) upon ongoing immunoglobulin (Ig) production and proliferation in human B cells was studied. ECP inhibited Ig production by the human lymphoblastoid cell lines, CBL and GM-1056, in a dose-dependent fashion. In contrast, proliferation was not affected. This ECP-induced inhibition of Ig production was specific, since inhibition was blocked by anti-ECP serum but not by control serum. Interleukin (IL)-4 did not affect Ig production by CBL or GM-1056 cells; however, IL-4 reversed ECP-induced inhibition of Ig production and this reverse was blocked by anti-IL-4 antibody but not by control antibody. In contrast, other cytokines, including IL-1 beta, IL-2, IL-3, IL-5, IL-6, interferon (IFN)-alpha, and IFN-gamma, failed to reverse inhibition. ECP also inhibited spontaneous Ig production (IgM, IgG1, IgG2, IgG3, IgG4, and IgA) by tonsillar large activated B cells without affecting proliferation. This inhibition was also blocked by anti-ECP serum but not by control serum and was reversed by IL-4 specifically. These results indicate that ECP may play an important role in B cell responses.