The postnatal development of gut lamina propria lymphocytes: number, proliferation, and T and B cell subsets in conventional and germ-free pigs.

The lamina propria (LP) contains many lymphocytes that are effector cells as well as memory cells of the gut immune system. This compartment was studied in normal and germ-free pigs in the early postnatal period up to 91 d of age. The number of LP lymphocytes nearly doubled between the 1st and 29th d. LP lymphocytes proliferated more in the crypt region than in the villi with a mitotic rate/h comparable to that in nonfollicular compartments of Peyer's patches and lymph nodes. The determination of the subpopulations of LP lymphocytes showed a 10-fold increase in CD2+ cells between d 1 and 40. About 80% of the LP T cells in 1- and 5-d-old pigs had the unusual CD2+CD4-CD8- phenotype. Ig-positive cells appeared later in the postnatal period than the T cells. On d 1, only a few IgM+ cells were observed. In 40-d-old animals, the number of IgA+ cells exceeded that of IgM+. Ten times more Ig+ cells were detected in the crypt region than in the villi. The germ-free pigs at an age of 49 d had a T cell subset pattern comparable to that of 5-d-old normal animals.