SOLUBLE HLA-G MOLECULE - AN ALTERNATIVELY SPLICED HLA-G MESSENGER-RNAFORM CANDIDATE TO ENCODE IT IN PERIPHERAL-BLOOD MONONUCLEAR-CELLS ANDHUMAN TROPHOBLASTS

The HLA-G nonclassic MHC class I gene expressed at the maternal-fetal interface may be involved in cell protection against NK cell lysis. HL A-G mRNA is observed in different adult or fetal human cells and exhib its four alternative forms: HLA-G1, HLA-G2, HLA-G3, and HLA-G4 lacking , respectively, exon 7; exons 7 and 3, exons 7, 3, and 4; exons 7 and 4. Because exon 5 encodes the transmembrane domain of the HLA-G antige n, none of these transcripts could give a soluble form as detected in supernatant of trophoblasts. In this report, we describe an additional alternatively spliced for of HLA-G transcript (HLA-G5) present in adu lt PBMCs and first-trimester trophoblasts that contains intron 4. More over, as with all other transcripts, HLA-G5, is devoid of exon 7. Its relative frequency is, respectively, similar to 1:8 and similar to 1:2 6 in adult PBMCs and first-trimester trophoblasts. The presence of int ron 4 generates a stop codon that excludes transmembrane region (exon 5) of the HLA-G molecule and therefore might produce a soluble antigen . These results are discussed with regard to data on soluble forms of classic HLA antigens and the possible role of HLA-G.