Role of interleukin-21 isoform in dextran sulfate sodium (DSS)-induced colitis.

Interleukin-21 (IL-21) is overproduced in human intestines affected by inflammatory bowel disease (IBD) and in the gut of mice with DSS-induced colitis. IL-21-deficient mice are largely protected against DSS-induced colitis, indicating that IL-21 plays a key role in the development of IBD. We previously identified a novel IL-21 isoform named IL-21iso. In this study, we found that in addition to the conventional IL-21, IL-21iso mRNA was also expressed in the colon with DSS-induced colitis. To investigate whether IL-21iso plays a role in DSS-induced colitis, we established transgenic mice (mIL-21iso-Tg mice) that expressed mouse IL-21iso under the control of the lck proximal promoter. Although mIL-21iso-Tg mice did not have any gross physical abnormalities, their peripheral lymphocytes counts were higher than those in wild-type littermates. Notably, their CD8(+) T cell and CD4(+) effector memory T-cell populations were elevated. DSS-induced colitis was far more severe in the mIL-21iso-Tg mice than in wild-type mice, and was accompanied by a marked loss of body weight and by colon inflammation with increased cellular infiltration. In DSS-treated mice, colon tissues from mIL-21iso-Tg mice had significantly higher gene activation levels for cytokines such as IL-17A, TNF-α, IL-6, IL-10, and IL-4, and for transcription factors such as T-bet, GATA-3, RORγt, and Foxp3, than were found in wild-type mice. These results indicate that besides IL-21, IL-21iso may be another regulator of gut inflammation.