AN ALTERNATIVELY SPLICED FORM OF HLA-G MESSENGER-RNA IN HUMAN TROPHOBLASTS AND EVIDENCE FOR THE PRESENCE OF HLA-G TRANSCRIPT IN ADULT LYMPHOCYTES

The HLA-G monomorphic, nonclassical class I gene encodes the major his tocompatibility complex (MHC) molecule, which is the only MHC antigen expressed on cytotrophoblast cells of placenta. In this work, we have investigated expression of the HLA-G gene in fetal tissues and adult p eripheral blood cells by using a sensitive hot-start reverse transcrip tase PCR technique. PCR amplification with HLA-G primers specific for exon 3 has enabled us to demonstrate an alternatively spliced form of HLA-G mRNA present in fetal first trimester trophoblasts and lacking e xon 4 (HLA-G.3-5). This low abundance transcript (approximate to 1:200 ) in comparison to full-length mRNA may encode the protein that exclud es the alpha 3 domain and by conformational changes may present a diff erent ability to bind to peptides. Moreover, expression of the HLA-G t ranscript was found in adult peripheral lymphocytes and equally in B- and T-cell populations. These results are discussed in the context of the fetal-maternal relationship presented by HLA-G gene products.