Evidence for Expression of Both Classical and Non‐Classical Major Histocompatibility Complex Class I Genes in Bovine Trophoblast Cells

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Abstract
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.

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