Ontogeny of pig discrete Peyer's patches: distribution and morphometric analysis

We investigated the development of lymphoid and non-lymphoid cells in discrete Peyer's patches (PP) of the pig using immuno-histology and image analysis. In newborn piglets discrete PP were mainly populated by CD2+, CD3+ T cells, and major histocompatibility complex class II+ cells, many of which were of macrophage and dendritic cell lineage. Four days after birth, cells were localized in defined regions: the follicle; the inter-follicular area and the dome region. Compartmentalization within the follicle started about 6 days after birth. The first signs of secondary follicles were seen from about 14 days. The pig discrete PP attained their mature structure at about 3 weeks after birth. Here we show that despite the demonstration at birth of the cell types that support antigen processing and presentation, PP did not fully differentiate morphologically until at least this time when antigen can be handled in an efficient manner.