Analysis of CCR5 expression on LP leukocytes in mice administered TNBS revealed that colitis development in this modelis mediated by the recruitment of three major leukocyte populations: MHC-II+ Gr-1− CD11bint cells (putative macrophages), MHC-II−Gr-1− CD11blow cells (likely monocytes/macrophages), and MHC-II− Gr-1+ CD11bhigh cells (putative granulocytes). The gene discussed is HLA-C; the disease is colitis.