Development of intestinal mucosal immunity in fetal life and the first postnatal months.

Nine premature infants who were either stillborn or who died shortly after delivery (gestational age, 24-32 wk), eight full-term infants who died during the first 3 postnatal wk, and four infants who died in the postneonatal period were studied by immunohistochemistry for duodenal expression of secretory component (SC) and epithelial HLA class I and II determinants and for the presence of IgA-, IgM-, and IgG-producing immunocytes. Only small amounts of SC appeared before the 29th gestational wk, but thereafter it increased rapidly; 1 wk after birth, SC showed an adult distribution pattern. Epithelial class I was expressed throughout the period investigated, whereas class II (HLA-DR) determinants were absent on the duodenal villi until 1 wk after birth. HLA-DP and -DQ were not expressed by the epithelium. No IgA immunocytes were seen before 1 wk after birth, whereas a few IgM- and IgG-producing cells were present throughout the period studied. The intense epithelial HLA-DR expression from the 2nd postnatal wk, along with SC and the appearance of IgA immunocytes, suggests that the intestinal immune system is modulated in response to environmental factors shortly after birth.