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.