Divalent cation regulation of the function of the leukocyte integrin LFA-1.
The integrin lymphocyte function-associated antigen-1 (LFA-1) expressed on T cells serves as a useful model for analysis of leukocyte integrin functional activity. We have assessed the role of divalent cations Mg2+, Ca2+, and Mn2+ in LFA-1 binding to ligand intercellular adhesion molecule-1 (ICAM-1) and induction of the divalent cation-dependent epitope recognized by mAb 24. Manganese strongly promoted both expression of the 24 epitope and T cell binding to ICAM-1 via LFA-1, suggesting that Mn2+ is able to directly alter the conformation of LFA-1 in a manner that favors ligand binding. Since Mn2+ also promotes functional activity of other integrins, parallels in mechanism of ligand binding may span the integrin family. In contrast, induction of 24 epitope expression by Mg2+ required removal of Ca2+ from T cell LFA-1 with EGTA. Furthermore, binding of mAb 24 to T cell LFA-1 in the presence of either Mn2+ or Mg2+ was found to be specifically inhibited by Ca2+, suggestive of a negative regulatory role for Ca2+ in the control of leukocyte integrin function. Analysis of T cell binding to ICAM-1 via LFA-1 in the presence of Mg2+ or Mn2+, confirmed that Ca2+ exerted inhibitory effects upon LFA-1 function. The implication of our findings is that Ca2+ bound with relatively high affinity to LFA-1 may serve to maintain an inactive state. Thus induction of function and 24 epitope expression may occur as a result of displacement of Ca2+ from leukocyte integrins or alternatively, such activators may be able to impose the required conformational change in the presence of bound Ca2+.
Macrophage Laboratory, Imperial Cancer Research Fund, London, England.
I
I
Dransfield
C
C
Cabañas
A
A
Craig
N
N
Hogg
D000818:Animals; D000911:Antibodies, Monoclonal; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D004492:Edetic Acid / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D018799:Intercellular Adhesion Molecule-1; D007700:Kinetics; D007739:L Cells; D016169:Lymphocyte Function-Associated Antigen-1 / Q000187:drug effects / Q000502:physiology*; D008274:Magnesium / Q000494:pharmacology*; D008345:Manganese / Q000494:pharmacology*; D051379:Mice; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology*; D014162:Transfection
D000911:Antibodies, Monoclonal; D002413:Cations, Divalent; D015815:Cell Adhesion Molecules; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1; D015240:Phorbol 12,13-Dibutyrate; D008345:Manganese; D004492:Edetic Acid; D008274:Magnesium; D002118:Calcium