Enterocyte IgG uptake in the small intestine of goat kids during the period of passive immunity acquisition

Abstract

The present study investigated enterocyte ultrastructure using transmission electron microscopy during IgG uptake in postnatal goat kids fed with colostrum. Six animals received 5% of body weight of goat colostrum at 0, 7 and 14h of life and were randomly slaughtered at 18, 36 and 96h (n=2) for the collection of duodenum, jejunum and ileum. Two other animals were sampled immediately after birth without colostrum ingestion constituting a 0h group. The enteric tissues were analyzed for ultrastructure enterocyte characteristics, immunocytochemistry labeling of immunoglobulin G (IgG), and microvillus height. In the duodenum, a large number of cytoplasmic organelles were observed. A dense network of tubular structures, the apical canalicular system (ACS), was observed only in the jejunum. At 0h, large vacuoles without electron-dense material were present in the cytoplasm of the enterocytes in this segment. At 18h, after the animals ingested three meals of colostrum, the vacuoles showed different sizes and were filled with electron-dense material. Labeled IgG were observed in the vacuoles containing colostrum and in the apical cytoplasm. At 36h, the ACS was still present as well as large vacuoles in the basal cytoplasm of the enterocytes and smaller vacuoles in the apical region. At 96h, the ACS and vacuoles with electron-dense material were no longer present. In the ileum, the cytoplasm of enterocytes showed a reduced presence of organelles and, at 0 and 18h, small vesicles were observed in the cytoplasm; however, they did not constitute a network of tubules. The ileum showed the lowest microvilli height (P<0.05), suggesting lower surface area to absorption compared to duodenum and jejunum. The jejunum segment was responsible for the initial acquisition of passive immunity and in the duodenum and ileum, a reduced capacity of IgG uptake was observed. On the fourth day of life, the enterocytes were no longer able to absorb macromolecules, indicating the end of the ability to uptake immunoglobulins.