Differences in altered expression of L-selectin and Mac-1 in monocytes and neutrophils

We have measured the altered expression of the adhesion-promoting glucoproteins L-selectin and Mac-1 on monocytes and neutrophils after incubation with different concentrations of the chemotactic factor FMLP. We found a time- and dose-related down-regulation of L-selectin on both monocytes and neutrophils, which was more pronounced on neutrophils as compared to monocytes at both low (10(-12) M) and high (10(-7) M) concentrations of the chemotactic factor FMLP. Presence of human albumin reduced the down-regulation of L-selectin on both monocytes and neutrophils but to a greater extent on monocytes. Mac-1 expression increased in a time and dose-dependent manner on both monocytes and neutrophils when they were incubated with both low (10(-12) M) and high (10(-7) M) concentrations of FMLP, but the expression was more pronounced on neutrophils. The up-regulation of Mac-1 was equally reduced by albumin on monocytes and neutrophils. Presence of EDTA in RPMI medium reduced the FMLP-induced down-regulation of L-selectin on both monocytes and neutrophils, indicating that the down-regulation of L-selectin is partly divalent cation dependent. Differences in the altered expression of L-selectin and Mac-1 in monocytes and neutrophils with sustained expression of L-selectin on monocytes can contribute to the sequential recruitment of these cells into an inflammatory site.