Antibody Testing for use in Immunohistochemistry and the Investigation of Precociously Induced Maturation of the Gastrointestinal Tract in Young Nude Rats

Sammanfattning: Background: Rat pups are born with an immature intestine adapted for the effective uptake of milk nutrients and with high permeability for bioactive molecules from the maternal milk until weaning. During weaning the immune system is activated after stimulation with e.g. dietary antigens, leading to an inflammatory response in the gut. This response is believed to be important for progress of gut maturation which involves changes in the small intestine from a foetal- to adult-like state. Recent studies indicate that immune cells, especially T cells, could play a key role in this and that treatment with immunosuppressive drugs delay gut maturation. The aim of this project was to further investigate the role of the immune system in the maturation of the gastrointestinal (GI) tract using immunodeficient nude young rats as the model. Methods: At first different antibodies were tested with immunohistochemistry (IHC) to see if they could be used in the investigation of GI maturation. Thymus deficient (NIH-Foxn1rnu, nude) suckling rats were treated with a dietary antigen (PHA) or a protease (trypsin) known to induce precocious GI maturation. Whereafter, the maturity of the intestines was investigated, i.e., organ growth and the proportion of adult-like epithelium was studied by morphometric methods and the presence of CD3+ cells was studied using IHC techniques. Results: The α-CD3 antibody was found to be useful for the further IHC studies of GI maturation. My combined results revealed that the treated nude rats showed intestinal maturation, similar to that seen at weaning in euthymic suckling rats. This included increased length of the proximal villi, tendency of increased crypt depth and change from foetal-like vacuolated cells to adult-like non-vacuolated cells in the distal epithelium. Surprisingly, CD3+ cells could be observed in the small intestine of the nude athymic young rats, however, in a lower amount than in the euthymic young rats. Conclusion: This study showed that the intestinal maturation process could be induced in nude young rats. However, since CD3+ cells could be detected in the nude rats this indicate that thymus-independent T cells might be involved in maturation of the gut after birth. These discoveries might lead to a better understanding of maturation of the GI tract and hopefully help in the search for treatment of Necrotizing Enterocolitis (NEC) in preterm humans born too early with an immature gut.