Problem: During the third trimester of pregnancy bovine trophoblast cells in the interplacentomal and arcade regions of the placenta express major histocompatibility complex class I (MHC-I) antigens. At parturition immunological recognition of MHC-I antigens appears to contribute to normal placental release. Therefore, we hypothesized that during late pregnancy bovine trophoblast cells express polymorphic, classical MHC-I antigens.
Method of study: Cloning, microarray screening and sequencing of cDNA were used to study transcription of MHC-I genes in peripheral blood mononuclear cells (PBMC) and interplacentomal, trophoblast cells. Real-time reverse transcription, polymerase chain reaction (RT-PCR) was used to compare the abundance of MHC-I transcripts in PBMC and trophoblast cells.
Results: Screening of cloned MHC-I cDNA on MHC-I microarrays indicated that in PBMC 90-98% of MHC-I transcripts were encoded by classical MHC-I genes with the remainder encoded by non-classical MHC-I genes. In contrast, 21-66% of MHC-I transcripts from interplacentomal trophoblast cells were from classical genes and 34-79% were from non-classical genes. Transcripts from four non-classical MHC-I loci were identified by sequence analysis. Real-time RT-PCR indicated that the overall levels of MHC-I gene expression in PBMC and trophoblast were similar.
Conclusion: Bovine interplacentomal trophoblast cells express both classical and non-classical MHC-I genes, but the relative level of expression varies considerably.