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.