Induction of cell surface human leukocyte antigen–G expression in pandemic H1N1 2009 and seasonal H1N1 influenza virus–infected patients

A novel H1N1 virus of swine origin (H1N1v) recently caused a pandemic; however, knowledge of immunologic aspects of the virus infection are limited. Human leukocyte antigen–G (HLA-G) was speculated to play critical roles in viral infection, although its clinical relevance in H1N1 infection remains unknown. In this study, HLA-G expression in peripheral T lymphocytes, monocytes, and CD4+ CD25+ FoxP3+ regulatory T (Treg) cells (in 50 H1N1v-infected and 41 seasonal H1N1–infected patients and 27 control subjects) were analyzed by flow cytometry. Plasma-soluble HLA-G (sHLA-G, in 28 H1N1v–infected, 29 seasonal H1N1–infected patients and 85 control subjects) were determined with enzyme-linked immunosorbent assay. The percentage of HLA-G–positive T lymphocytes and monocytes among patients with H1N1v and seasonal H1N1 infections was dramatically increased compared with controls (all p < 0.001). Treg was markedly increased among H1N1v- infected patients compared with normal controls (p = 0.041), but not for the seasonal H1N1–infected patients. Meanwhile, no significant difference was observed for sHLA-G levels between the groups. Together, cell surface HLA-G expression was markedly induced in H1N1v–infected and seasonal H1N1–infected patients, and increased Treg was observed only in H1N1v-infected patients. Given its immune-suppressive property, elevated cell surface HLA-G expression may help to explain the virus escaping from host immune responses.