However, Kawamoto et al. [30] investigated the effect of the PD-1/PD-L1 pathway on the enteric microbiota and reported a significant decrease in the relative abundance of P. aeruginosa and Bifidobacteria in the intestinal microbiota of PD-1−/− mice, whereas Vetizou et al. [31] were followed to show that the introduction of Bacteroides fragilis alleviated colitis caused by cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibition. This evidence concerns the gene CTLA4 and colitis.