Differentiation of B cells in the bovine. Role of cytokines in immunoglobulin isotype expression.

Cytokines such as IFN-gamma, IL-4 and TGF-beta, are known to regulate Ig class switching by positively or negatively regulating germline CH transcription in the mouse and human. Here we show at the protein level that similar regulatory mechanisms are in place in the bovine using various modes of B cell activation and cytokine combinations. Using antigen-receptor cross-linkage or mitogen (pokeweed mitogen) costimulation, we demonstrate that recombinant bovine IL-4 upregulates the expression of IgM, IgG1 and IgE in vitro. Upregulation of IgG1 and IgE production by rboIL-4 is inhibited in a dose-dependent manner by the addition or rboIFN-gamma to the cultures. Using similar methodologies, we have also investigated the effects of TGB-beta on IgA production in the presence or absence of various cofactors including IL-10 and IL-2. We find that TGF-beta will not solely upregulate IgA production from noncommitted precursors (sIgM+) in coculture with mitogen or with formalin fixed Staphylococcus cowan Strain I (SAC), but does have positive effects on IgA production in the presence of both IL-2 and IL-10. These observations suggest that different modes of T-independent costimulation using classical B cell activators does not result in differential IgG subisotype or IgE production by bovine B cells in the presence of cytokines. Together these results suggest that individual cytokines regulate isotype expression in cattle.