CD4 and arthritic joint disease: While B cells regulate disease progression and resolution in wild-type mice (McKisic and Barthold, 2000), adoptive transfer of CD4+ T cells into RAG-deficient mice prior to B. burgdorferi infection increased arthritis and carditis severity (unless B cells were co-transferred), and CD8+ T cell transfer increased arthritis severity (McKisic et al., 2000).