Costimulatory Molecule CD28Participates In The Process Of Embryo Implantation In Mice

ObjectiveEmbryo implantation is a complex process requiring reciprocalinteractions between implantation competent blastocysts and receptive uteri.The maternal immune system will produce a series of complex and subtlechanges in order to adapt the process of embryo implantation. Under theregulation of neuro-endocrine-immune system, endometrium of thematernal uteri during peri-implantation period will form immunemicroenvironment which is beneficial to embryo implantation. Thesubstances constitute immune microenvironment are mainly immune cellsand inflammatory factors. T cell is an important kind of immune cell in thematernal-fetal interface. The first signal mediated by TCR/CD3complexand the second signal delivered by costimulatory molecule CD28areessential for the differentiation of T cell into an effector cell. Our previousmicroarray results have showed that the expression of CD28are significantdifferent between implantation sites and inter-implantation sites during “implantation window”. We presume that the difference may be related tothe embryo implantation process. The expression and function of CD28during early pregnancy in mice is still unclear. To better understand theimmune regulative function of embryo implantation, we investigated theexpression pattern of CD28in mouse uterus during early pregnancy andpseudopregnancy, and studied its function during embryo implantationprocess.Methods(1) Investigate the expression pattern of CD28in mouse uterus duringearly pregnancy and pseudopregnancy by real-time quantitative PCR,western blotting, in situ hybridization and immunohistochemistry. Examinethe expression pattern of CD3by immunohistochemistry to detect whetherthe first signal (CD3) and the second signal (CD28) for the activation of Tcells co-exist in the uterus.(2) Count the number of implantation sites after injection of theuterine horn with CD28antisense oligodeoxynucleotides. The implantationsites and inter-implantation sites of pregnancy were identified byintravenous injection through tail vein of Chicago blue.Results(1) We found that the spatial and temporal expression pattern of CD28in mouse uterus during early pregnancy and pseudopregnancy. The mRNA and protein of CD28on D5is much higher than other days of earlypregnancy, while during early pseudopregnancy days there is no peak. Therelative mRNA expression at implantation sites is lower thaninter-implantation sites on D5. The expression pattern of CD3proteinexamined by immunohistochemistry is similar to that of CD28.(2) Injection of the uterine horn with CD28antisenseoligodeoxynucleotides leads to a decreased number of implantation sites.ConclusionThe results showed that the expression pattern of CD28in mouseendometria has a spatial temporal characteristic during early pregnancy andpseudopregnancy. The high level of CD28in mouse endometria during the“implantation window” suggests that CD28may be involved in the processof embryo implantation. We speculate the role may be relevant tocostimulatory signal delivered by CD28in stroma. However, the detailedmechanism by which CD28fulfills its role in implantation needs furtherexploration.