Surface expression of differentiation antigens on lymphocytes in the ileal and jejunal Peyer's patches of lambs.

The surface phenotype of lymphocytes in the ileal (IPP) and jejunal (JPP) Peyer's patches (PP) of lambs was compared using flow cytometry and immunohistology with a panel of monoclonal antibodies (mAb). The B-cell markers p220, BAS9A and surface Ig molecules were detected on 70-95% of cells from the IPP. T-cell markers were detected on less than 1% of IPP lymphocytes, confirming that the IPP in lambs contains virtually only B lymphocytes. The JPP contained a lower proportion of B cells and 16% T cells, nearly all of which expressed the CD4 molecule. Interestingly, the reactivity of a fourth B-cell markers, BAQ44a, differed from this pattern; only 12% of IPP lymphocytes were positive whereas 70% of JPP lymphocytes expressed this marker. A majority of both IPP and JPP lymphocytes (80-95%) expressed the cell adhesion molecules CD11a (LFA-1) and LFA-3. Other adhesion molecules, such as CD2 and CD44, were expressed by fewer cells from the IPP than from the JPP. MHC class I antigens were detected on more than 95% of lymphocytes from both the IPP and JPP. In the case of MHC class II antigens, more positive cells occurred in the IPP (greater than 95%) than in the JPP (80%). The in situ localization of cell-surface antigens was assessed by immunohistology. CD4+ T cells occurred in the interfollicular T-cell regions and in JPP follicles, whereas CD8+ T cells localized only in the interfollicular regions and were absent from follicles. The pattern of expression of B-cell markers, adhesion molecules and MHC antigens indicated that a gradient of increasing maturity of B cells existed within follicles from the base towards the dome region. The data presented here lend support to the notion that the IPP in lambs represents a novel B-cell lymphoid tissue with a function different from that of the conventional Peyer's patches found in the jejunum.