Qa-2 mRNA in peripheral blood mononuclear cells: a potential marker of acute allograft rejection

HLA-G displays an immunotolerogenic role and its expressions in grafts/sera are related to allograft acceptance. However, it is still unclear how its transcription level in peripheral blood mononuclear cells (PBMCs) changes during allograft rejection. The aim of the present study was to detect the expression changes of the murine homolog of HLA-G, Qa-2, serially during the whole process of graft rejection with mouse skin transplantation models and to investigate their relationship with the pathological grade of graft rejection and immunosuppressive therapy.

Full-thickness skin derived from donor mice (C57BL/6j for syngeneic groups and Balb/c for allogeneic groups) was transplanted onto the dorsal thorax of recipient mice (C57BL/6j). Pathological allograft changes were classified into four grades. Qa-2 mRNA expression of PBMCs was detected serially by real-time RT-PCR.

Qa-2 mRNA did not show any obvious change in the syngeneic recipients without immunosuppressive treatment, inferring that surgical stress might not influence Qa-2 expression. A significant increase in Qa-2 mRNA was observed in the immunosuppressant-treated recipients, suggesting that the increased Qa-2 mRNA level might be attributed to the immunosuppressive treatment. During allograft rejection, the Qa-2 mRNA level decreased significantly, especially with immunosuppressive treatment, and the decreased expression was detected when the allograft presented grade 2-3 pathological rejection, much earlier than when gross rejection was observed.

These results suggest that decreased expression of Qa-2 mRNA in PBMCs may be a potential marker for predicting acute allograft rejection as well as a tool to monitor the effects of immunosuppressive treatment.