B Cell Development and T-Dependent Antibody Response Are Regulated by p38γ and p38δ

p38MAP kinase (MAPK) signal transduction pathways are important regulators of inflammation and the immune response; their involvement in immune cell development and function is still largely unknown. Here we analysed the role of the p38 MAPK isoforms p38gamma and p38delta in B cell differentiation in bone marrow (BM) and spleen, using mice lacking p38gamma and p38delta, or conditional knockout mice that lack both p38gamma and p38delta specifically in the B cell compartment. We found that the B cell differentiation programme in the BM was not affected in p38gamma/delta-deficient mice. Moreover, these mice had reduced numbers of peripheral B cells as well as altered marginal zone B cell differentiation in the spleen. Expression of co-stimulatory proteins and activation markers in p38gamma/delta-deficient B cells are diminished in response to B cell receptor (BCR) and CD40 stimulation; p38gamma and p38delta were necessary for B cell proliferation induced by BCR and CD40 but not by TLR4 signaling. Furthermore, p38gamma/delta-null mice produced significantly lower antibody responses to T-dependent antigens. Our results identify unreported functions for p38gamma and p38delta in B cells and in the T-dependent humoral response; and show that the combined activity of these kinases is needed for peripheral B cell differentiation and function.