DO HUMAN PEYER PATCHES CONTRIBUTE TO THE INTESTINAL INTRAEPITHELIAL-GAMMA-DELTA T-CELL POPULATION

T-cell receptor gamma/delta+ (TCRgamma/delta+) lymphocytes in human Pe yer's patches (PP) adjoining ileal mucosa were studied by monoclonal a ntibodies with paired immunofluorescence staining in situ and by flow- cytometric phenotyping of isolated cells. The proportion of gamma/delt a+ T cells in the follicle-associated epithelium outside the M-cell ar eas (median 4.1%, range 2.2-30.1%) was similar to that in mucosal vill ous epithelium (median 4.4%, range 0.5-30.5%). Most intraepithelial ga mma/delta cells (approximately 90%) expressed CD45R0 but only a few ex pressed CD8 (< 10%) and none L-Selectin; a dominating subset (median 4 6%) employed the Vdelta1/Jdelta1 gene product (range 22-100%). The M-c ell areas lacked gamma/delta cells but contained clustered CD20+ and C D3+ lymphocytes. The subepithelial PP dome area and interfollicular (T -cell) zones, as well as the mucosal lamina propria, contained very fe w gamma/delta cells (median 1.7%, range 0.4-8.9%) which were dominated (88-100%) by the Vdelta2-encoded subset. Those in the dome area and l amina propria were often (approximately 75%) CD45R0+ (range 44-90%) wh ile very few (approximately 2%) expressed L-selectin (range 0-15%). By contrast, CD45R0 expression on gamma/delta cells in the PP T-cell zon es was relatively low ( approximately 46%) and that of L-selectin rela tively high (approximately 43%). In conclusion, TcR gamma/delta+ cells are quite rare in human PP and belong mainly to the Vdelta2-encoded s ubset, thus being different from most intraepithelial gamma/delta cell s that probably have another origin. The L-selectin+ fraction of PP ga mma/delta cells presumably represent newly recruited 'naive' T lymphoc ytes while CD45R0+ gamma/delta cells both in PP and lamina propria are probably antigen-primed.