Uptake of colostral immunoglobulins by the suckling rat

The sequential appearance of immunoglobulins was studied in serum samples from rats during the suckling period. At birth both IgG1 and IgG2 were present, but IgM was not detected until the 7th day and IgA until the 17th day. No intestinal transmission of intact homologous IgA was demonstrable after oral administration of radiolabelled preparations (125I) of either serum or colostral IgA to suckling rats. When 125I labelled IgG 2a+b rat immunoglobulins were given orally there was a selective transport of the slower moving subclass from the gut into the serum. The rat appeared to differ from several other species in which some intestinal absorption of passively transferred IgA by the newborn has been demonstrated. It was suggested that retention of colostral and milk IgA in the intestine may serve to enhance local defense mechanisms in the newborn rat.