CD40-deficient mice infected with the defective murine leukemia virus LP-BM5def do not develop murine AIDS but produce IgE and IgG1 in vivo.

CD40-deficient mice, when inoculated with the LP-BM5def murine retorvirus, become infected and show virus expression similar to wild-type mice. However, unlike the wild-type mice, CD40-deficient mice do not develop symptoms of immunodeficiency, lymphoproliferative disease and the typical histological changes in the lymphoid tissue. These results show that the CD40-CD40 ligand (CD40L) interaction in vivo is essential for anergy induction and the subsequent development of immunodeficiency and pathologic expansion of lymphocytes. Infected CD40-deficient mice and their littermates express a similar pattern of cytokine mRNA, which is not biased towards a Th2 phenotype. Nevertheless, hypergammaglobulinemia is induced in infected wild-type and CD40-deficient mice. Surprisingly, murine AIDS infection even induces IgE production in CD40-deficient mice in vivo. Our data demonstrate that antibody class switch to IgE and IgG1 can be induced by a retroviral infection in vivo even in the absence of CD40-CD40L interaction and an apparent switch to a Th2 cytokine production.