Infection of susceptible C57BL/6 mice with defective LP-BM5 murine leukemia virus causes disease termed murine acquired immune deficiency syndrome (MAIDS). The disease is characterized by lymphoadenopathy, hyperimmunoglobulinemia, and immune deficiency in both T and B cell functions. The development of disease requires the presence of mature T cells, especially CD4 T cells, and B cells. It has previously been shown that a B cell tumor line derived from MAIDS mouse stimulated a large fraction of unprimed T cells based on TCR V beta chain expression. This stimulatory activity was assumed to be mediated by a superantigen encoded by MAIDS virus. The stimulation of T cells by viral superantigen was thought to play a role in the development of the disease. To examine the role of T cell reactivity to MAIDS superantigen, we used TCR transgenic mice. There are two distinct T cell populations which can be distinguished based on their TCR expression and function in the TCR transgenic mice, one bearing the transgene derived alpha- and beta-chain TCR that is nonreactive to MAIDS superantigen and the other bearing an endogenous alpha- but transgene-derived beta-chain TCR that is reactive to superantigen. Unlike T cells found in noninfected TCR transgenic mice, anergic T cells expanding in virally infected TCR transgenic mice are homogeneous for the TCR phenotype, indicating the presence of a selection of T cells based on their TCR expression. T cell hybridomas established by fusing T cells from virus-infected transgenic mice to thymoma cell line are also anergic. We found mRNA of defective LP-BM5 virus in a majority of T cell hybridomas from virus-infected mice but not from noninfected mice. By using in vitro infection of T cell clones with recombinant virus containing LP-BM5 MAIDS virus gag gene, we have demonstrated that virus infection directly abrogated the Ag-specific reactivity of T cells. The establishment of anergic T cell hybridomas and the in vitro infection of T cells with recombinant viruses would be a useful tool in the analysis of biochemical and molecular mechanisms of T cell dysfunction in MAIDS.