In vitro IgE but not IgG production of canine peripheral blood B cells is inhibited by CD40 ligation

The aim of this study was to investigate in vitro IgE induction in peripher al canine B cells. CD21(+) B cells were purified from the peripheral blood of beagle dogs by positive selection via magnetic separation to a purity of greater than or equal to 95%. Subsequently, proliferation, and IgG and IgE production of canine B cells were investigated after stimulation with huma n recombinant Interleukin-4 (hrIL-4) and human recombinant Interleukin-2 (h rIL-2) in the presence or absence of CD40L-CD8 fusion protein (CD40L) of mo use origin. We could demonstrate that canine B cells react on hrIL-2 alone by proliferation and IgG production but not by IgE secretion, whereas activ ation with hrIL-4 induced proliferation and mainly IgE production. Together , both cytokines synergistically increased B cell proliferation as well as IgG and IgE production. We could also show that mouse CD40L induces prolife ration of dog B cells, which is further enhanced by addition of hrIL-4. Une xpectedly, CD40L led to a dramatic decrease in the IL-4 mediated IgE secret ion (82% inhibition on an average). In contrast, IgG production was not aff ected significantly by CD40L. The same effects of CD40L were observed when B cells were stimulated by a combination of IL-2 and IL-4 and this inhibiti on could not be abrogated by increasing the amounts of IL-4. In summary, ac tivation of canine B cells from peripheral blood by hrIL-4 in the presence or absence of hrIL-2 led to marked IgE production that is strongly and in a dose-dependent manner inhibited by CD40L. Stimulation of IgG production is not influenced by CD40L. (C) 2000 Elsevier Science B.V. All rights reserve d.