Ontogeny of the gut-associated lymphoid system in man.

Immunoperoxidase histochemistry using monoclonal antibodies to lymphoid/myeloid cells has been used to study the development of the human mucosal immune system in frozen sections of foetal human intestine at different ages. A steady progression of development was seen between 11 and 19 weeks' gestation. At 11 weeks, Peyer's patches were identifiable only as aggregates of strongly HLA-DR+ cells. By 16 weeks these aggregates became colonized with T and B cells, without distinct cellular zonation. By 19 weeks primary B-cell follicles were seen and T cells occupied the inter-follicular zones. There was also a steady increase in the numbers of lamina propria and epithelial T cells between 11 and 19 weeks' gestation. As in postnatal bowel, CD8+ cells predominated in the epithelium and CD4+ cells predominated in the lamina propria. Thus the important T- and B-cell compartments of the mucosal immune system are well established in the human foetal intestine by mid-gestation.