IMMUNOHISTOCHEMICAL STUDIES OF THE PERITONEAL MEMBRANE AND INFILTRATING CELLS IN NORMAL SUBJECTS AND IN PATIENTS ON CAPD

Immunohistochemical studies on the peritoneal membrane and infiltratin g cells in normal subjects and in patients on CAPD. We performed immun ohistochemical studies on biopsies of the parietal peritoneal membrane of 33 subjects to investigate whether other cell populations, in addi tion to mononuclear cells free in the dialysate, might participate in the defense of the peritoneum against microbial invasion during CAPD. Leukocytes were found to concentrate in two areas: a submesothelial la yer composed of elongated macrophages displaying activation and matura tion markers, and perivascular, less mature macrophages closely associ ated with T cells and HLA-DR, ICAM-1 and VCAM-1 expressing endothelial cells. Normal mesothelial cells were found to express constitutively the transferrin receptor and the adhesion molecules ICAM-1 and VCAM-1 but not ELAM-1. There were no major differences between normal and ure mic subjects, while peritoneal dialysis patients exhibited minor deran gements of the submesothelial layer and slight up-regulation of the ex pression of HLA-DR on endothelial cells. Peritonitis was associated wi th increased submesothelial cellularity and, particularly, perivascula r leukocyte infiltration accompanied by increased expression of HLA-DR and adhesion molecules. Besides mononuclear cells free in the dialysa te, this study demonstrates the existence of two additional peritoneal membrane leukocyte populations: submesothelial macrophages, and periv ascular macrophages and T cells. It also suggests the existence of a f ourth population of intracavitary leukocytes adherent to mesothelial c ells. Studies are now necessary to evaluate their exact role in the ho st defence against peritonitis during CAPD.