CD4 and myeloid sarcoma: Although chemokine receptors are normally upregulated in differentiating T cells, enabling them to migrate and home to the location of ongoing immune responses, CCL2 and CCL4 have been detected at high levels in the cerebrospinal fluid, brain tissue, and active lesions of patients with MS, and elevated expression of both chemokine receptors on pathogenic CD4+ T cells has been correlated with the active phase of MS (57, 65, 66).