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We have recently been able to correlate closely the "spontaneous" oscillatory activity of cytosolic free Ca2+ in adherent human neutrophils with the ability of tumor necrosis factor (TNF) to induce secretion of granule proteins from these cells. In the present work we show with a single-cell technique that preincubation of human neutrophils with antibodies to CD18, the common beta chain of leukocyte adhesion proteins, inhibits TNF-induced secretion of lactoferrin in a time- and concentration-dependent manner. Similar effects of CD18 antibodies were found on chemotactic factor (fMet-Leu-Phe)- but not on phorbol 12-myristate 13-acetate-induced secretion, suggesting that cell-surface-receptor-mediated secretion is dependent on integrin-associated signals. Similarly, antibodies to CD11b (alpha chain of macrophage 1) also inhibited TNF- and fMet-Leu-Phe- but not phorbol 12-myristate 13-acetate-stimulated release of lactoferrin. Antibodies to CD11a (alpha chain of lymphocyte function-associated antigen 1) or CD11c (alpha chain of p150,95) had only a minimal effect on agonist-induced secretion. Data obtained in several laboratories, including our own, made us suspect that integrin interaction with the surface is responsible for the oscillatory activity of cytosolic free Ca2+ in adherent cells. Indeed, preincubation with antibodies to either CD18 or CD11b, but not to CD11c, inhibited the oscillations of cytosolic free Ca2+ in adherent neutrophils. This inhibitory effect was evident both as a reduction of the number of responding cells and as a reduction of the oscillatory activity in the cells. In conclusion, the oscillatory activity of cytosolic free Ca2+ in adherent neutrophils is mediated through the CD18/CD11b integrins. The generation of this Ca2+ signal may explain how adherence, by way of the integrins, changes the functional properties of the cell and enables TNF to induce secretion.

proceedings of the national academy of sciences of the united states of america

Tumor necrosis factor-induced degranulation in adherent human neutrophils is dependent on CD11b/CD18-integrin-triggered oscillations of cytosolic free Ca2+.