CD4 and myeloid sarcoma: Susceptibility to MS is genetically linked to major histocompatibility complex (MHC) genes and genes associated with T cell activation and homeostasis; however, the strongest genetic linkage occurs with certain alleles of MHC class II, which suggests a direct relationship between autoreactive CD4+ T cells and MS disease development in humans (Hillert and Olerup, 1993; Fogdell-Hahn et al., 2000; Sospedra and Martin, 2005).