Ontogeny of systemic and enteric immune system development and morphological characteristics in neonatal pigs under conventional and segregated early weaning conditions

An experiment was conducted to evaluate immune system development and gut morphology in neonatal pigs: (1) pre-weaning; and (2) post-weaning reared under conventional (Conv) and segregated early weaning (SEW) conditions. Prior to weaning, there are changes in the phenotypic expression of blood lymphocytes in addition to a greater functional capacity of these immune cells as the pig increases in age. During the first few weeks of life the young pig may rely on gammadelta T-cell activity and later, once the pig experiences antigen and gets closer to weaning, it relies on further development of the alphabeta T cell repertoire, in addition to the development of the gammadelta T-cell repertoire and population of cytotoxic T cells. Before weaning, the young pig is experiencing alterations in villi width, crypt depth and the number of intestinal sulfuric goblet cells. These changes occurring prior to weaning in lymphocyte phenotypic expression and functional capabilities as well as mucin production may be to further protect the neonate from antigenic stimuli as passive immunity declines. At weaning, the pigs gut architecture is further altered as seen by villus atrophy and crypt hyperplasia; however, there were no alterations due to pig rearing environment. The pigs' immune cell and goblet cell populations are continuing to develop in the intestine after weaning and seem to be further affected by the pigs rearing environment. There was an earlier expansion of CD8+, CD25+ and gammadeltaTCR+ cells in the intestine of SEW pigs than CONV pigs. There were also changes in the number of acidic and sulfuric goblet cells and CD4+ cells over the post-weaning period due to the pigs rearing environment. These changes observed in goblet cells and immune cells in the intestine of newly weaned pigs may be in response to commensal microflora and specific bacteria species entering the intestinal tract, which may play an important role in orchestrating the balance between the inflammatory response and tolerance in the newly weaned pig creating a homeostatic environment where the young pig has the best chance for growth and survival, and may account for the greater growth performance seen in SEW pigs.