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. Howeve r, unlike the wild-type mice, CD40-deficient mice do not develop symptoms o f immunodeficiency, lymphoproliferative disease and the typical histologica l changes in the lymphoid tissue. These results show that the CD40-CD40 lig and (CD40L) interaction in vivo is essential for anergy induction and the s ubsequent development of immunodeficiency and pathologic expansion of lymph ocytes. Infected CD40-deficient mice and their littermates express a simila r pattern of cytokine mRNA, which is not biased towards a Th2 phenotype. Ne vertheless, hypergammaglobulinemia is induced in infected wild-type and CD4 0-deficient mice. Surprisingly, murine AIDS infection even induces IgE prod uction in CD40-deficient mice in vivo. Our data demonstrate that antibody c lass switch to IgE and IgG1 can be induced by a retroviral infection in viv o even in the absence of CD40-CD40L interaction and an apparent switch to a Th2 cytokine production.