CLDN1 and ulcerative colitis: The effect of 1,25D3 on TM-induced expression of TJP in the IPEC-J2 spheroids is in line with findings in active ulcerative colitis patients, in which increased protein levels of CLDN1 and CLDN2 and elevated pro-inflammatory cytokine levels (IL6 and IL13) in the colonic mucosa were decreased by 1,25D3 [28].