Abstract:
Introduction: Minor histocompatibility antigens were identified as causing organ transplant rejection in HLAmatched donor/recipient pairs (1). Polymorphisms in minor histocompatibility antigens induce immune reactions targeting the ‘non-self’ variant proteins causing graft rejection (1). The semiallogeneic fetus may induce similar immunological reactions in the mother due to expression of paternally-derived minor histocompatibility antigens, potentially influencing pregnancy outcomes (2). Proteins containing minor histocompatibility antigenic peptides were identified in fetal tissue (3- 6). However, in most cases the specific expression of the minor histocompatibility antigenic peptides was not confirmed. Aims: 1. To investigate specific placental expression of sex-specific and autosomal minor histocompatibility antigens at the mRNA level. 2. To investigate using sex-specific minor histocompatibility antigens in sexing tissue samples. 3. To generate an RPS4Y1 minor histocompatibility antigen-specific antisera to detect protein expression of the RPS4Y1 minor histocompatibility antigen. Methods: RT-PCR and Sanger sequencing were used to examine mRNA expression of RPS4Y1, UTY, DDX3Y, ERAP1 and HA-1 minor histocompatibility antigens in first trimester and term placentae. Antisera reactive with the RPS4Y1 minor histocompatibility antigen was generated and used to probe placental thin sections and Western blots of peripheral blood mononuclear cells and a placental lysate. Results: An SRY specific PCR-based sexing system was used to assign 24 of the 41 placentae as male. RPS4Y1 minor histocompatibility antigen mRNA was expressed by 27 placentae, of which 24 expressed SRY. UTY minor histocompatibility antigen mRNA was expressed by 24 placentae, of which 22 expressed SRY. A DDX3 amplicon was produced in 40 placentae, and two DDX3Y minor histocompatibility antigens were identified by sequencing of two SRY expressing placentae. Twenty four of the 37 placentae expressed the ERAP1 minor histocompatibility antigen, and three of the 14 placentae expressed the HA-1 minor histocompatibility antigen. The two RPS4Y1 minor histocompatibility antigen-reactive antisera could not differentiate between Y and X chromosome variants. Staining of the placental thin sections was unsuccessful, Western blotting of peripheral blood mononuclear cells and a placental lysate using one of the two RPS4 antiserum produced bands at approximately 30kDa and 40kDa. Conclusions: RPS4Y1, UTY, DDX3Y, and ERAP1 minor histocompatibility antigen mRNA was identified in first trimester and term placentae. HA-1 minor histocompatibility antigen mRNA was also identified in first trimester placentae. Consequently, the placenta is a potential source of fetal minor histocompatibility antigens which could stimulate the maternal immune system.