Changes in the expression of adhesion molecules as peripheral blood monocytes differentiate into peritoneal macrophages

Peritoneal macrophages, derived from peripheral blood monocytes, are the chief cellular defenders against invasion of the peritoneal cavity by infectious organisms. Monocyte migration into the peritoneal cavity depends upon a coordinated series of adhesive events, utilizing cell surface receptors known as adhesion molecules. In order to better understand the mechanisms of leucocyte infiltration of the peritoneum during peritonitis, we studied the relative expression of adhesion molecules on monocytes and peritoneal macrophages from patients on continuous ambulatory peritoneal dialysis (CAPD). Peripheral blood and spent peritoneal dialysis fluid were obtained from patients undergoing CAPD, and the level of expression of various adhesion molecules on the monocytes/macrophages analysed by flow cytometry using receptor-specific monoclonal antibodies. Monocytes were also purified from the peripheral blood of volunteer donors, cultured in vitro for varying periods, and analysed in the same manner. Consistent differences in expression of certain adhesion molecules were found between monocytes and peritoneal macrophages, and similar changes occurred on monocytes cultured in vitro. Concurrent infection had no clear effect. Several receptors (integrins alpha 4 beta 1, alpha 6 beta 1, alpha L beta(2) and aIIb beta 3, and platelet endothelial cell adhesion molecule-1) were significantly decreased on peritoneal macrophages, while only the integrin alpha v beta 5 increased. It is concluded that monocyte differentiation into peritoneal macrophages is accompanied by characteristic alterations in the adhesion molecule repertoire on the cell surface, emphasizing the different adhesive requirements of these two cell types.