Involvement of type I immune responses in swine-origin H1N1 influenza virus infection

Swine-origin H1N1 influenza virus (S-OIV) appeared in 2009 with a higher incidence rate among children. Although fever was the most common symptom, some complicated cases occurred. We evaluated the percentages of effector T cells, B cells, and regulatory T cells in peripheral blood from 5 children infected by S-OIV (1 with acute necrotizing encephalitis, 2 with pneumonia, and 2 without complications), 5 children with seasonal influenza, and 5 healthy children. We found higher percentages of T-bet+ CD4+CD8+ T cells, monocytes, and B cells, granzyme B+ and perforin+ CD4+, and CD8+ T cells in affected children with both seasonal and H1N1 influenza than in controls, whereas both groups demonstrated similar percentages of CD4+CD25+Foxp3+ regulatory T cells. In infected children with complications we observed high percentages of perforin+ and interferon-γ+ CD4+ and CD8+ T cells associated with low percentages of T regulatory cells. Our data suggest a dysregulation of antipathogen type I immune responses in complicated S-OIV infections.