Effect of early weaning on the development of immune cells in the pig small intestine.

The controlled effects of age and weaning on the numbers of CD2+ T cells, subsets (CD4+, CD8+), accessory cells (macrophage/granulocyte) and cells expressing MHC class II (DQw) and IL-2R in the piglet intestine was investigated. At birth low numbers of CD2+CD4-CD8- cells were the only demonstrable T cells in the intestine. Monocyte/granulocyte and MHC class II+ cells were also detected in low numbers and IL-2R+ cells were proportionally quite numerous. All those cell populations, except the IL-2R+ cells, increased thereafter and peaked at Week 7 when the numbers of cells were comparable with those of adult animals. CD4+ cells increased dramatically after Week 1. In contrast, CD8+ remained scarce until after 5-7 weeks of age in unweaned animals. Four days after weaning at 3 weeks old, there were increases in CD2+ (P < 0.001) and macrophage/granulocyte (P < 0.01) cells in proximal small intestinal villi and in CD2+ cells only (P < 0.01) in crypts. No significant changes in cell numbers were demonstrated in the distal small intestine.