The role of CD4+ T cells in MS has been further demonstrated by the strongest genetic susceptibility conferred by HLA class II alleles (15), susceptibility of HLA class II-carrying mice to demyelinating disease (33–36), presence of CD4+ T cells in inflammatory brain lesions (37), and the involvement of CD4+ T cells in several other arms of adaptive immunity such as antibody production and CD8+ T cell maturation. This evidence concerns the gene CD4 and myeloid sarcoma.