PECAM1 and myeloid sarcoma: The extent to which the observed changes in TFH - and Th17-phenotypes and recent thymic emigrants are associated with functional changes in immune reactivity must be established in functional studies, but we hypothesize that the changes in TFH phenotype may reflect an increased potential for TFH interactions with B-cells and that the decrease in CD31+T-cells may reflect an increased memory and effector T-cell pool in patients with progressive MS.