EARLY STAGES OF INTESTINAL ABSORPTION OF SPECIFIC ANTIBODIES IN THE NEWBORN An Ultrastructural, Cytochemical, and Immunological Study in the Pig, Rat, and Rabbit

In mammals, passive immunity is transferred from mother to offspring by transplacental passage or by intestinal absorption . The rabbit receives antibodies exclusively across the placenta, whereas intestinal absorption is the principal source of antibodies for the newborn pig. In the rat, passive immunity is transferred by both pathways . The role of the jejunal absorptive cells was investigated in these three species, by the use of specific immune globulins as tracers of protein absorption . Rabbit anti-peroxidase and anti-ferritin antibodies were injected into the jejunum of newborn pigs, rats, and rabbits, and absorption was studied over the first 2 hr. The specific antibodies were detected in glutaraldehydefixed tissues after in vitro treatment with the antigens, and in sera by immunological methods. Intact antibodies are transferred into the circulation of the pig and the rat, but not into that of the rabbit . In the three species, the jejunal absorptive cells take up antibodies by endocytosis. In the pig, the antibodies are transported across the epithelium in vacuoles . In the rabbit, the endocytosis of antibodies triggers a lysosomal response and all absorbed antibodies are trapped in lysosomes . In the rat, both situations are found ; there is no evidence of transfer of antibody fragments into the circulation . When passive immunity is transferred across the placenta, as in the rabbit, the guinea-pig, and the human, the mechanism of intestinal absorption of antibodies does not occur (6, 12, 42, 43, 65, 66) . The mouse, rat, dog, and cat represent an intermediate group in which antibodies are transmitted both across the placenta and by intestinal absorption after birth (14, 15, 17, 41, 84) . The rat receives before birth about one-third of its passive immunity (9, 24) . The rate of intestinal absorption in the newborn rat is very high fo . homologous antibodies, and moderate for mouse and rabbit antibodies ; cow antibodies are not absorbed (2, 3, 25) . Antibody absorption in the rat decreases gradually after the first day and stops completely at the age of 21 days (25) . In the pig, rat, and rabbit, striking and apparently similar histological changes occur in the intestinal columnar absorptive cells during protein 3 45 on A uust 4, 2017 jcb.rress.org D ow nladed fom absorption . A vesicular and vacuolar apparatus develops after birth in the absorptive cells when they are in contact with colostrum or proteins (11, 30, 31, 67, 81, 82) . Animals which have not been suckled show only few vacuoles (55) . These morphological features seem in contradiction to the differences of protein absorption capacities in the three species . To investigate this apparent contradiction, the initial steps of intestinal absorption of well characterized proteins, i .e . rabbit antiperoxidase and anti-ferritin immunoglobulins G (IgG)' were studied by morphological and immunological methods. Preliminary results were reported recently .' MATERIALS AND METHODS Experimental Procedure The animals in these experiments were six newborn piglets (Sus crofa domesticus L.) which had been separated from the sow immediately after birth and before any ingestion of colostrum ; 40 newborn albino rats (Rattus norvegicus Berk., Wistar strain), 10 of which were used under the same conditions as the pigs for morphological investigations; and 25 newborn rabbits (Oryctolagus cuniculus L .), six of which were obtained by uterotomy at term. The rats and rabbits were anesthetized by hypothermy in a cold room at 4 °C. The piglets received an intraperitoneal injection of 40 mg of sodium barbiturate (Eunarcon, Riedel, Berlin) per kg of body weight. A 7% solution of purified rabbit anti-peroxidase or anti-ferritin IgG, 2 ml per 100 g of body weight, was injected into the first part of the jejunum during laparotomy. Jejunal tissues were fixed 15, 30, 45, 60, 90, and 120 min after IgG administration, and blood samples were taken at the same intervals . Blood samples were obtained in rats and rabbits by decapitation, and in piglets by umbilical vein cannulation . Immunological Procedures