Activation of bovine B cells via surface immunoglobulin M cross‐linking or CD40 ligation results in different B‐cell phenotypes

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Abstract
Experiments reported herein demonstrate that activation of bovine B cells via surface immunoglobulin M (sIgM) cross-linking, analogous to T-cell independent (TI-2) antigenic stimulation, results in the expression of CD5. Interestingly, in the presence of CD40 ligand, sIgM-mediated induction of CD5 on B cells was inhibited. These findings indicate that activation of bovine B cells via B-cell receptor (BCR) cross-linking results in a CD5+ B-cell phenotype and that CD40 signalling is inhibitory to this process. Analysis of cytokine mRNA indicates that bovine B cells constitutively express tumour necrosis factor-α (TNF-α) and interleukin (IL)-1β transcripts in vitro, while IL-10 mRNA expression is induced following sIgM cross-linking. IL-12 p40 transcripts were produced by B cells activated by CD40, but not by BCR, ligation. Analysis of cytokine receptor mRNA indicates that activation through CD40, in the presence or absence of IgM cross-linking, results in increased IL-4 receptor-α (IL-4Rα), IL-13Rα1 and interferon-α receptor 1 (IFN-αR1) mRNA levels. Overall, these findings suggest that activation of bovine B cells through BCR cross-linking yields an activation phenotype that differs substantially from that of B cells activated through CD40.