Interaction of leukocyte integrins with ligand is necessary but not sufficient for function.
The leukocyte integrins (CD11/CD18 or beta 2-type integrins) are expressed exclusively on leukocytes and participate in many adhesion-dependent functions (Arnaout, M.A. 1990. Blood. 75:1037-1050; Springer, T. A. 1990. Nature. (Lond.) 346:425-434; Dustin, M. L., and T. S. Springer. 1991. Annu. Rev. Immunol. 9:27-66). The avidity of leukocyte integrin binding to their ligands or counter-receptors is dependent upon response to intracellular signals (Wright, S. D., and B. C. Meyer. 1986. J. Immunol. 136:1759-1764; Dustin, M. A., and T. S. Springer. 1989. Nature (Lond.). 341:619-624). We have investigated the effects of a novel mAb (mAb 24) which defines a leukocyte integrin alpha subunit epitope that is Mg(2+)-dependent and may be used as a "reporter" of the activation state of these receptors (Dransfield, I., and N. Hogg. 1989. EMBO (Eur. Mol. Biol. Organ) J. 8:3759-3765; Dransfield, I., A.-M. Buckle, and N. Hogg. 1990. Immunol. Rev. 114:29-44; Dransfield, I., C. Cabañas, A. Craig, and N. Hogg. 1992. J. Cell Biol.) Data is presented to show that this mAb inhibits monocyte-dependent, antigen-specific T cell proliferation and IL-2-activated natural killer cell assays which are both dependent on lymphocyte function-associated antigen-1 (LFA-1), and complement receptor type 3 (CR3)-mediated neutrophil chemotaxis to f-Met-Leu-Phe. This inhibitory effect is not caused by the prevention of receptor/ligand binding because LFA-1/ICAM-1, LFA-1/ICAM-2,3 and CR3/iC3b interactions are, under activating conditions, promoted rather than blocked by mAb 24. As it does not interfere with mitogen-stimulated T cell proliferation, it is unlikely that mAb 24 transduces a "negative" or antiproliferative signal to the T cells to which it is bound. Using a model system of transient activation of LFA-1, we have found that mAb 24 prevents "deadhesion" of receptor/ligand pairs, possibly locking leukocyte integrins in an "active" conformation. It is speculated that inhibition of leukocyte integrin function by this mAb reflects the necessity for dynamic leukocyte integrin/ligand interactions.
Dransfield
I
I
Macrophage Laboratory, Imperial Cancer Research Fund, London, England.
Cabañas
C
C
Barrett
J
J
Hogg
N
N
D000911:Antibodies, Monoclonal; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002449:Cell Aggregation; D002460:Cell Line; D002634:Chemotaxis, Leukocyte; D003179:Complement C3b / Q000378:metabolism; D003602:Cytotoxicity, Immunologic; D006801:Humans; D015979:Killer Cells, Lymphokine-Activated / Q000276:immunology; D008213:Lymphocyte Activation; D016169:Lymphocyte Function-Associated Antigen-1 / Q000276:immunology / Q000378:metabolism*; D016177:Macrophage-1 Antigen / Q000276:immunology / Q000378:metabolism*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000502:physiology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology*; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D015815:Cell Adhesion Molecules; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen; D015240:Phorbol 12,13-Dibutyrate; D009240:N-Formylmethionine Leucyl-Phenylalanine; D003179:Complement C3b