As human ulcerative colitis is associated with signs of chronic colonic inflammation, they investigated whether the increased susceptibility to acute inflammation associated with defective CCL25/CCR9 interactions would also translate into increased susceptibility to chronic inflammation, and found that chronic DSS exposure results in exacerbated colitis in mice deficient for either CCR9 or CCL25 when compared with WT control mice. Here, CCR9 is linked to ulcerative colitis.