Recruitment of circulating leukocytes into the colonic tissue is a key feature of intestinal inflammation. P-selectin glycoprotein ligand-1 (PSGL-1) and very late antigen-4 (VLA-4) are expressed on leukocytes and play an important role in leukocyte-endothelial cell adhesive interactions. We examined the effects of immunoneutralization of PSGL-1 and VLA-4 on leukocyte recruitment in vivo in the development and treatment of experimental colitis. Chronic colitis was induced in balb/c mice by oral administration of dextran sodium sulfate (DSS). Monoclonal antibodies 2PH1 (anti-PSGL-1) and PS/2 (anti-VLA-4) or the combination of both were injected intravenously, and leukocyte adhesion was observed for 60 min in colonic submucosal venules by intravital microscopy (IVM) under isoflurane/N(2)O anesthesia. In addition, mice with established colitis were treated by daily intraperitoneal injections of 2PH1, PS/2, or the combination of both over 5 days. Disease activity index (DAI), histology, and myeloperoxidase (MPO) levels were compared with sham-treated DSS controls. We found that 2PH1 reduced the number of rolling leukocytes (148.7 +/- 29.8 vs. 36.9 +/- 8.7/0.01 mm(2)/30 s, P < 0.05), whereas leukocyte velocity was increased (24.0 +/- 3.6 vs. 127.8 +/- 11.7 microm/s, P < 0.05). PS/2 reduced leukocyte rolling to a lesser extent. Leukocyte firm adhesion was not influenced by 2PH1 but was strongly reduced by PS/2 (24.1 +/- 2 vs. 4.4 +/- 0.9/0.01 mm(2)/30 s, P < 0.05). Combined application did not cause additional effects on leukocyte adhesion. Treatment of chronic colitis with 2PH1 or PS/2 reduced DAI, mucosal injury, and MPO levels significantly. Combined treatment led to a significantly better reduction of DAI (0.4 +/- 0.1 vs. 2.1 +/- 0.2 points) and histology (9.7 +/- 0.9 vs. 21.4 +/- 4.6 points). In conclusion, PSGL-1 and VLA-4 play an important role for leukocyte recruitment during intestinal inflammation. Therapeutic strategies designed to disrupt interactions mediated by PSGL-1 and/or VLA-4 may prove beneficial in treatment of chronic colitis.