Jejunal and ileal Peyer's patches in pigs differ in their postnatal development

The postnatal development of the jejunal and ileal Peyer's patches was studied before and after weaning in 1-, 1.5- and 2-month-old pigs. The follicles of the jejunal Peyer's patches grew with age and were two times longer and wider in specified pathogen-free and conventional pigs than in germ-free animals, thus indicating an influence of the living microbial antigens from the gut lumen. In germ-free pigs the size of the ileal Peyer's patch follicles increased between the 1st and 2nd month, whereas in the specified pathogen-free and conventional animals these follicles were comparable in size in all three age groups. In 1- to 1.5-month-old pigs the interfollicular area of jejunal Peyer's patches was wider (0.1 +/- 0.04 mm) than that of the ileal Peyer's patch (0.04 +/- 0.03 mm). Immunohistological studies showed that in germ-free pigs preferentially surface IgM+ but few IgA+ B cells were present in the follicles, domes and dome epithelia. In specified pathogen-free and conventional pigs the B cells expressed different levels of surface or cytoplasmic IgM or IgA. In all groups studied, more T cells were observed in the jejunal than in the ileal Peyer's patch. Here, few T lymphocytes were found because of the small interfollicular areas. Small numbers of Null cells were distributed in the interfollicular regions of all animals. The results show that living microbial antigens have a major influence on the jejunal and ileal Peyer's patches in pigs. The morphological differences between the two types of Peyer's patches are an indication that they develop differently during postnatal life. So far it remains unclear whether these morphological differences reflect a specific function of the pig's ileal Peyer's patch, such as the expansion of the genetically determined B cell repertoire as has been reported for sheep.