ICOS and ulcerative colitis: During the active phase of ulcerative colitis (UC), ICOS+, PD-1+ and ICOS+PD-1+ Tfh cells levels were significantly elevated, and significantly decreased upon reaching clinical remission; activated ICOS+PD-1+ Tfh cells were positively correlated with serum C-reactive protein (CRP) and Mayo scores, and ICOS+PD-1+ Tfh cells also correlated significantly with circulating new memory B cells, plasmablasts, and serum IgG, IL-4, and IL-21, suggesting that ICOS and PD-1 are involved in UC pathogenesis [113].