CD38 and systemic lupus erythematosus: When SLE and HC samples were combined, we did, however, find that IgA− PB/PC (that is, IgG+ and IgM+ PB/PC) expressed higher levels of CD38 compared to their IgA+ counterparts (1.2-fold, p = 0.07) and that mean CD38 expression levels were higher on HLA-DRhigh PB compared to HLA-DRlow PC (1.4-fold increase, p = 0.01).