Importantly, the discovery of bidirectional exchange of B cell clones between the CNS compartment and the periphery gave strong credence to the possibility that in MS patients, memory B cells contribute to MS pathology by acting as the APCs that reactivate encephalitogenic CD4+ T cells and subsequently produce proinflammatory cytokines that further contribute to inflammation and damage within the CNS (43, 78). Here, CD4 is linked to myeloid sarcoma.