The Crohn's disease-associated bacterial protein I2 is a novel enteric T cell superantigen

An aberrant T cell response to enteric bacteria is important in inflammator y bowel disease. However, the identity of relevant microbial antigens is un known. Here, we report the presence of I2, a Crohn's disease-associated mic robial gene, in the murine intestine. The I2 protein induced a proliferativ e and IL-10 response by CD4(+) T cells from unimmunized mice. The I2 respon se was dependent on MHC class I1-mediated recognition but did not require a ntigen processing. Selective activation was observed for the TCR-V beta5 su bpopulation. These findings indicate that the I2 protein is a new class of T cell superantigen and suggest that colonization by the I2 microorganism i n susceptible hosts may provide a superantigenic stimulus pertinent to Croh n's disease pathogenesis.