Selective induction of CD11a,b,c/CD18 and CD54 expression at the cell surface of human leukocytes by muramyl peptides

Muramyl dipeptide (MDP), murametide, and murabutide which belong to the family of the immunoadjuvant muramyl dipeptides were applied directly to fresh human whole blood and the expression of some surface markers involved in cell adherence in distinct leukocyte populations was investigated. CD11a,b,c/CD18, CD54, and CD49d were selected for their involvement in cell adherence, and transferrin receptor (CD71) and low-affinity IgE receptor (CD23) were selected as markers for activated cells. Whereas CD11a was increased only on monocytes, CD11b, CD11c, and CD18 were strongly enhanced on monocytes and polymorphonuclear cells (PMNs) after treatment with MDPs. This increase in membrane expression of integrins, such as CD11b, was not associated with mRNA synthesis, suggesting a mobilization of the CD11b,c/CD18 intracellular pools present in these cells. In contrast, treatment with MDP, murametide, or murabutide enhanced ICAM-1 (CD54) expression on monocyte and PMN cell surface in association with ICAM-1 mRNA synthesis. No variation of CD49d expression was detected on leukocyte surface after incubation with MDPs. Transferrin receptor (CD71) expression and low-affinity receptor for IgE (CD23) expression were increased on monocyte only after incubation with LPS used as positive control. Moreover, no observable change in the selected markers was detected on lymphocyte after MDPs or LPS treatment. These results indicate that MDPs seem to act preferentially on monocytes and PMNs in increasing the level of molecules involved in cellular adhesion process, either in provoking the expression of preformed molecules or in inducing their synthesis. This contributes to understanding the mechanism of the activities of muramyl peptides on specific and nonspecific immunity.