We previously demonstrated in rabbits that various neutrophil chemotactic factors share an ability to induce recruitment of polymorphonuclear leukocytes (PMN) from bone marrow when administered intravenously (Jagels and Hugli, J Immunol 148:1119, 1992). In the study reported here, we investigated the effects of chemotactic factors on the expression of beta 2 integrins and L-selectin in vivo and the roles of these adhesionmolecules in the recruitment process. Leukocytosis was induced by infusion of either C5a (5 micrograms/kg), N-formyl-methionyl-leucyl-phenylalanine (f-MLP; 2.5 micrograms/kg), or tumor necrosis factor alpha (TNF-alpha; 100 ng/kg). C5a increased the expression of CD18 (the common subunit of beta 2 integrins) on PMN by nearly twofold and decreased levels of L-selectin by 50% within 15 minutes after administration. Levels of beta 2 integrins returned to baseline 2 to 3 hours after induction of leukocytosis. L-selectin remained depressed for more than 5 hours, demonstrating that shedding was induced in the recruited bone marrow leukocytes as well as in circulating PMN. In contrast to the response to C5a, TNF-alpha did not cause upregulation of CD18 or shedding of L-selectin. Levels of L-selectin were consistently increased 60 minutes after administration of TNF-alpha, coinciding with a rapid rise in the number of band-form PMN in the circulation. Intact IgG and F(ab)2 forms of the anti-CD18 monoclonal antibody IB4 or the anti-L-selectin antibody DREG-200 were administered intravenously 15 minutes before induction of leukocytosis by the chemotactic factors. Neither IB4 nor its F(ab)2 fragments blocked leukocytosis induced by C5a, f-MLP, or TNF-alpha. DREG-200 also did not block leukocytosis induced by f-MLP, C5a, or TNF-alpha. These results suggest that leukocyte emigration from the bone marrow into the circulation proceeds through interactions distinct from those involved in neutrophil chemotaxis and diapedesis. Shedding of L-selectin from C5a-recruited bone marrow leukocytes demonstrates activation of these cells in the recruitment process and may reflect a potential mechanism for their release. The dissimilar effects of C5a and TNF-alpha on expression of adhesion molecules may result from distinct stimulatory pathways and suggests differential activation states for cellular recruitment by these inflammatory factors.