Segregation of B lymphocytes into stationary apoptotic and migratory proliferating subpopulations in agglomerate cultures with ileal epithelium

The B lymphocyte-epithelial cell interactions that define the microenvironm ent of the ileal Peyer's patch, the primary B lymphocyte organ of the fetal lamb, have been replicated in tissue culture. Mixed suspensions of Real ep ithelial cells, lymphocytes and fibroblasts from fetuses of 63-103 days of gestation organized into macroscopically visible agglomerates within 72 h. These agglomerates contained translucent spherical cavities and were enclos ed within a marginal cell layer and surrounded by an expanding corona of em igrating cells. The lining of the cavities and the marginal layer consisted of well-differentiated, polarized columnar ilea[ epithelial cells. One pop ulation of B lymphocytes in the initial mixed suspension differentiated int o two discrete populations reproducing the characteristics of intact fetal ileal Peyer's patches. B cells apposed to follicle-associated epithelium (F AE) within agglomerates underwent apoptosis. The other population of emigra nt B cells proliferated and expressed the BAQ44A differentiation marker. Di fferentiation of ilea[ epithelial cells into FAE, typical of Peyer's patche s, was markedly accelerated. The mutually inductive influences of intestina l epithelial cells and B lymphocytes in these agglomerates replicate normal mid-gestational fetal development of the mucosal immune system and afford new opportunities for its further investigation.