Defective IL-5-receptor-mediated Signaling in B Cells of X-linked Immunodeficient Mice

Murine (m) IL-5 induces proliferation and differentiation of both Ly-1+ B cells and activated conventional B cells. X-linked immunodeficient (XID) mice do not respond to thymus-independent type II antigens, and have an abnormal response to a variety of activation signals through Ig receptors, CD40 and cytokine receptors. Furthermore, XID mice show a B cell specific defect, reflected in decreased numbers of IL-5R alpha+ B cells and reduced responsiveness of IL-5R alpha+ B cells to mIL-5. We generated IL-5R alpha transgenic (5R alpha-Tg) mice in which B cells expressed recombinant IL-5R alpha. We crossed male 5R alpha-Tg mice with female XID mice and used their offspring to determine the IL-5 responsiveness of these B cells. All B cells of F1 male mice carrying the xid gene together with the transgene expressed the recombinant IL-5R alpha. However, those mice lacked Ly-1 B cells and their B cells acquired responsiveness to mIL-5. Interestingly, XID-5R alpha-Tg B cells, but not XID B cells, acquired mIL-5 proliferative and Ig-secretory responsiveness only in the presence of suboptimal doses of lipopolysaccharide. Stimulation of these B cells with mIL-5 plus phorbol myristate acetate induced proliferation, but not Ig secretion. These results indicate that the impaired mIL-5 responsiveness of B cells in XID mice is due to an abnormality of IL-5R-mediated signaling which may correlate with the xid gene mutation, alteration of a single amino acid of Bruton's tyrosine kinase.