CD38 and rheumatoid arthritis: In seropositive synovial samples from patients with RA, activated PD-1+CXCR5+ and PD1+CXCR5- CD4+ T cells, also expressing HLA-DR and CD38, were found adjacent to B cells.40 Moreover in CD, Martin et al observed the production of CXCL13, a B cell attractant, in a subset of T cells that expressed HLA-DR and CD38 mRNA in samples from inflamed ileum.33 Collectively, these results suggest that activated CD4+ T cells could provide B cell help.