Altered Levels of Immune Checkpoint Molecules in Colon Biopsies and Sera from Microscopic Colitis and Ulcerative Colitis Patients Compared to Controls

Abstract Background: Microscopic colitis (MC), comprising lymphocytic colitis (LC) and collagenous colitis (CC), is an inflammatory bowel disorder. MC patients have a lower risk of developing colorectal cancer (CRC) than ulcerative colitis (UC) patients. We hypothesize that the immune response in MC is geared more towards immune surveillance of tumor cells than that of UC, which instead contributes to inflammation-associated CRC. Methods: Using Luminex, protein levels of 14 immune checkpoints (TIM-3, CD28, CD137, CD27, CD152, HVEM, IDO, LAG-3, BTLA, GITR, CD80, PD-1, PD-L1, PD-L2) in protein lysates from colon biopsies (controls, n = 9; diarrhea controls, n = 7; LC, n = 14; CC, n = 15; UC, n = 17) were analyzed. Soluble checkpoints were analyzed in serum (23 controls, 17 LC, 36 CC and 2 UC). Results: In patients with active LC and CC, CD137, IDO, and CD80 levels were increased compared with one or both control groups. CD152 and PD-1 levels were increased in patients with active CC compared with both control groups. In patients with active UC, levels of CD137, CD152, BTLA, PD-1, and PD-L2 were increased compared with both control groups, IDO levels were increased compared with controls, and CD80 levels were raised compared with diarrhea controls. In sera, CD27, IDO, CD80, PD-1, and PD-L2 levels were decreased in LC patients compared to controls. Conclusions: Increased levels of immune checkpoint molecules in colon biopsies from UC and MC patients are likely a sign of inflammation and may indicate what kind of homeostatic feed-back mechanisms are active to balance inflammation. Lowered concentrations of soluble immune checkpoint molecules in sera from patients with LC indicate a different level of homeostatic balance systemically in LC patients versus controls.