The most important findings are that (a) HBO2 significantly reduces symptoms and severity of DSS-induced colitis, as evidenced by clinical appearance, contraction of the immune cell expansion and mobilization, and reversal of IL-1β, IL-2, and IL-6 gene expression; (b) HBO2 modulates the expression of antioxidative enzyme genes and enzyme activities during colitis; and (c) HBO2 enhances HIF-1α mRNA expression in the inflamed colonic tissue which is in a strong correlation with GPx1, SOD1, and IL-6 mRNA expression. Here, IL2 is linked to colitis.