Characterization of B-cell phenotypic changes during ileal and jejunal Peyer's patch development in sheep

Changes in B-cell phenotype during development of ileal and jejunal Peyer's patches (PP) of sheep were investigated using flow cytometry and immunoperoxidase-stained cryosections. On Day 104 of gestation (term at 150 days) B-cell clusters were identified in the lamina propria of the ileum. These clusters were composed of cells that expressed surface IgM (sIgM), lambda or kappa light chain, and BAQ44A, a B-cell differentiation molecule. No cells in the clusters stained for terminal deoxynucleotide transferase. On Day 132 gestation, a change was evident in the phenotype of ileal PP B cells. Most B cells expressed a reduced level of sIgM and 20% were BAQ44A-. The B cells in the dome region were BAQ44A+ but few BAQ44A+ cells were present in the follicles. At 6-8 weeks of age BAQ44A+ cells were restricted to the dome region of the ileal PP; flow cytometric analysis confirmed that 25% of B cells isolated from the dome/follicle complex were BAQ44A+. Thus, the primordial PP was populated with B cells that were phenotypically similar to circulating B cells (sIgMhigh, BAQ44A+). After 132 days gestation, the predominant B-cell phenotype in the ileal PP changed to sIgMlow and BAQ44A-. This phenotypic change could be the result of either early immigrant B-cell differentiation or subsequent colonization by sIgMlow BAQ44A- B cells. The phenotypic changes of ileal PP follicular B cells were not complete until after birth and different phenotypic changes were observed in follicles of the jejunal PP of young lambs.