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The Journal of Immunology, Vol 149, Issue 5 1497-1503, Copyright © 1992 by American Association of Immunologists
ARTICLES |
B Damaj, W Mourad and PH Naccache
Department of Medicine, Universite Laval, Ste. Foy, Quebec, Canada.
The present study was designed to examine the potential involvement of calcium ions as second messengers in the mediation of the staphylococcal enterotoxin A (SEA)/MHC class II-induced activation of human monocytes. Treatment of monocytes with a monomeric form of SEA failed to induce detectable changes in the level of intracellular calcium in either monocytes or THP-1 cells. However, cross-linking of SEA with biotin-avidin induced a rapid and transient increase in calcium levels in monocytes and in INF-gamma-treated THP-1 cells. This artificial cross-linking system was reproduced by natural physiologic ligands expressed on the surface of T lymphocytes. Delayed, transient, and concentration (cell as well as toxin)-dependent increases in the cytoplasmic level of free calcium in SEA-treated monocytes were observed upon the addition of autologous resting T cells or purified CD4+ cells, but not of CD8+ cells, B cells, or neutrophils. Antibodies against MHC class II Ag, TCR/CD3, and CD4 molecules inhibited the SEA- dependent interaction between monocytes and T cells as indicated by significant decreases in the rise of calcium levels observed in monocytes. Anti-CD8 and anti-class I antibodies did not affect the interaction between the monocytes and the T cells and failed to alter the calcium response. Taken together, these results suggest that the SEA-induced, T cell-dependent calcium mobilization in monocytes requires physical interactions between SEA-MHC class II, TCR/CD3, and CD4 molecules. The ability to mediate a T cell-dependent calcium increase in monocytes was shared by several enterotoxins including staphylococcal enterotoxin B and toxic shock syndrome toxin-1. The characteristics of the SEA-mediated calcium mobilization in monocytes strongly support the hypothesis that this response is an integral part of the signal transducing machinery linked to MHC class II molecules.
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