Inflammatory bowel disease (IBD) is a chronic, disabling disease. A dysregulated immune response seems to play a pivotal role in the pathogenesis of this disorder. Here we will review current concepts of the adoptive transfer model of IBD with particular emphasis on early events in disease development. In the adoptive transfer model, the reconstitution of immunoincompetent mice with CD4+ T cells from congenic donor animals leads to severe colitis. We will address the question as to which CD4+ T cell subsets might be involved in the induction, suppression, or regulation of disease, and review data concerning the specificity of their T cell receptor and its putative MHC restriction elements. We will also discuss whether and at what anatomical sites donor T cells could be primed in the recipient. Copyright 2003 S. Karger AG, Basel