PSI-3 Major Histocompatibility Complex gene expression profile in bovine pairs submitted to fixed time artificial insemination (FTAI).

Abstract The Major Histocompatibility Complex (MHC) is a set of genes crucial for immune response regulation, playing a fundamental role in defending against pathogens and maintaining immune tolerance during pregnancy. MHC genes expression affects the interaction between the maternal immune system and the embryo, being one of the factors responsible for embryonic recognition and pregnancy success. This study aimed to compare the expression of MHC-I, NC-1, NC-2, NC-3, and NC-4 genes in bovine pairs subjected to Fixed Time Artificial Insemination (FTAI), divided into two groups: successful pregnancy (FTAI+) and unsuccessful pregnancy (FTAI-). Blood samples were collected from ten females and one bull of the Braford breed, and gene expression analysis was performed using RT-PCR. The average expression for each pair was calculated by the arithmetic mean of values obtained from the female and the male. Statistical analysis was performed using the Unpaired t-test in GraphPad Prism 8.01 Software. The results revealed that the expression of the analyzed MHC genes was significantly higher in the FTAI- group, suggesting a possible association between higher gene expression and failure to maintain pregnancy. The FTAI- group exhibited higher expression of the MHC-I gene compared to the FTAI+ control group, and this pattern was consistent in all pairs (5/5)(p< 0.05). In the analysis of non-classical MHC genes, NC-1, NC-2, and NC-3, the expression was increased in most FTAI- pairs (3/5)(p< 0.05). However, no significant difference was observed for the NC-4 gene between the FTAI+ and FTAI- groups (0/5)(p >0.05). Among the five genes analyzed, only NC-1 and NC-3 have well-established functions in the literature. NC-1 stimulates the maternal immune response, while NC-3 inhibits it, thereby protecting the fetus. MHC-I, NC-2, and NC-4 genes have been linked to pregnancy success in various species, but their roles still need further clarification. Based on these findings, we conclude that the elevated expression of MHC genes in the FTAI- group suggests that an increase in the expression of these genes could be associated with pregnancy loss. Although the expression of NC-1, NC-2, and NC-3 varied, an increase in the expression of these genes may affect the maternal immune response, influencing embryonic tolerance and pregnancy success. These results underscore the need for further studies to investigate the link between MHC gene expression and reproductive success. Furthermore, they highlight the complexity of immune mechanisms involved in bovine reproduction and, consequently, the success of FTAI.