Knockout of Mkp-1 not only accelerates the induction of colitis but also exacerbates the severity of colitis in Il-10 knockout mice. Mkp-1+/+/Il-10+/+, Mkp-1+/+/Il-10−/−, Mkp-1+/−/Il-10−/−, and Mkp-1−/−/Il-10−/− mice housed in a SPF environment were monitored weekly to score the severity of their colitis. The clinical scoring criteria included 6 parameters: loss of more than 5% of body weight, rectal prolapse, perianal mucus, rectal bleeding, wet stool consistency, and death. Mice were given a score of either 0 (parameter absent) or 1 (parameter present) for each parameter (maximum possible score per mouse = 6). Scores in the graph were averaged from individual animals in each group (n = 20–24 per group) and presented as means ± SE. *P < 0.05, compared with Mkp-1+/+/Il-10−/− mice; ‡P < 0.05, compared with Mkp-1+/+/Il-10+/+ mice (Student's t-test). Note the more severe disease in Mkp-1+/−/Il-10−/− mice relative to Mkp-1+/+/Il-10−/− mice.