The frequencies of CD38+IgA+ (cluster 11) and CD38+IgM+ (cluster 13) plasma B cells were significantly reduced in UC patients compared to CD patients and non‐IBD controls, whereas CD38+ (cluster 8), CD38+HLA‐DR+IgA− (cluster 9), and CD38+IgM− (cluster 12) B cells were markedly expanded in UC patients compared to non‐inflamed controls. The gene discussed is CD40LG; the disease is inflammatory bowel disease.