Impact of blood processing on estimation of soluble HLA-G

HLA-G is a non-classical MHC class I antigen that functions as an immunomodulatory molecule. There are two forms of HLA-G antigens, soluble and membrane bound. Soluble HLA-G can be produced by translation of HLA-G transcripts (HLA-G5, -G6, -G7) and by shedding/proteolytic cleavage of membrane bound antigens (HLA-G1, -G2, -G3, -G4). Soluble as well as membrane bound HLA-G molecules have a direct inhibitory effect on immune responses. The relevance of soluble HLA-G in various pathologic conditions, such as transplantation, autoimmunity, infectious and malignant diseases, has been extensively investigated, however interpretation remains controversial. In this work we analyzed the levels of sHLA-G (sHLA-G1 and HLA-G5) in different blood samples of healthy donors as serum, and blood plasma isolated using anti-coagulant EDTA and heparin, respectively. We found that the levels of sHLA-G (sHLA-G1 and HLA-G5) in blood plasma prepared with EDTA were significantly higher than those observed in plasma with heparin or in serum. Finally we detected the average levels of sHLA-G in females exceeded those of males.