DISTRIBUTION OF HUMAN COLONIC DENDRITIC CELLS AND MACROPHAGES

To define the phenotype of intestinal dendritic cells and macrophages, resected colonic specimens were used to obtain lamina propria cell su spensions by EDTA treatment, then enzymatic digestion. The phenotype o f dendritic cell-enriched suspensions was compared with that of macrop hage-enriched populations by immunocytochemistry using the avidin-biot in-peroxidase (ABC) system and immunoelectron microscopy. Dendritic ce lls expressed HLA-DR (L243) and HLA-DQ-associated (RFD1) antigens and CD68 in a perinuclear distribution. Staining for S100 was weak or abse nt. Macrophages also expressed HLA markers (L243 and RFD1) and CD68. T he 25F9 antigen was expressed strongly, whilst CD14 was absent from ce lls isolated from noninflamed tissues. To determine their anatomic dis tribution, immunohistochemistry was performed using single- and double -labelling techniques (ABC +/- alkaline phosphatase anti-alkaline phos phatase method). Mutually exclusive subsets of 25F9(+) and S100(+) cel ls were seen: 25F9(+) macrophages were concentrated in a band immediat ely beneath the luminal epithelium; S100(+)/HLA-DR(+) dendritic cells formed a reticular network throughout the lamina propria and beneath t he basement membrane of the crypts. This distribution suggests that ma crophages may help regulate intestinal responses by acting as the firs t line of defence against the entry of luminal antigens. A breach of t he macrophage 'barrier' by invading antigens may necessitate the recru itment of T cell responses by immunostimulatory dendritic cells.