The influence of divalent cations and doxycycline on iodoacetamide-inhibitable leukocyte adherence.

Leukocyte adherence, an event critical to host defense, is reported to be dependent upon divalent cations. To test whether leukocyte binding is more influenced by the availability of Ca2+ or Mg2+, neutrophils and mononuclear leukocyte adherence to surfaces coated with differing proteins, in medium containing varying concentrations of Ca2+ and/or Mg2+ and induced with either FMLP or PMA were assessed. To account for nonspecific leukocyte-substrata interactions the OD's of iodoacetamide-inhibited adherent cell systems were subtracted from the OD values of adherent cells of noninhibited systems. Values presented were derived from OD's of iodoacetamide-inhibitable leukocyte binding. PMA was a much more potent inducer of leukocyte adherence than was FMLP, stimulating all available neutrophils and monocytes to adhere. In contrast, FMLP induced adherence by roughly 1/4 of the available neutrophils and few, if any, monocytes. Roughly the same binding pattern was noted whether surfaces were coated with albumin, fibrinogen, fibronectin, gelatin or serum. EDTA but not EGTA significantly suppressed leukocyte binding suggesting Mg2+ was more involved in binding than was Ca2+. Little leukocyte adherence to a substrata occurred in the absence of divalent cations, while enrichment of the medium with Mg2+ was more influential on cell binding than was enrichment with Ca2+. Interestingly, doxycycline, a member of the tetracycline family of drugs which has been reported to inhibit Mg(2+)-dependent neutrophil functions, had a slight inhibitory effect on neutrophil adherence at low drug concentrations, while it enhanced binding at higher doxycycline concentrations. In contrast, the tetracycline inhibited monocyte adherence in a dose-related manner.