Clearance of influenza virus infections by T cells: risk of collateral damage?

Influenza A viruses are a major cause of respiratory infections in humans. To protect against influenza, vaccines mainly aim at the induction of antibodies against the two surface proteins and do not protect against influenza A viruses from other subtypes. There is an increasing interest in heterosubtypic immunity that does protect against different subtypes. CD8 and CD4 T cells have a beneficial effect on the course of influenza A virus infection and can recognize conserved IAV epitopes. The T cell responses are tightly regulated to avoid collateral damage due to overreaction. Different studies have shown that an aberrant T cell response to an influenza virus infection could be harmful and could contribute to immunopathology. Here we discuss the recent findings on the balance between the beneficial and detrimental effects of T cell responses in influenza virus infections.

Characterization of the human CD8⁺ T cell response following infection with 2009 pandemic influenza H1N1 virus.

The 2009 H1N1 influenza pandemic provided an opportunity to study human virus-specific T cell responses after infection with a novel influenza virus against which limited humoral immunity existed in the population. Here we describe the magnitude, kinetics, and nature of the virus-specific T cell response using intracellular gamma interferon (IFN-γ) staining and fluorochrome-labeled major histocompatibility complex (MHC) class I-peptide complexes. We demonstrate that influenza virus-infected patients develop recall T cell responses that peak within 1 week postinfection and that contract rapidly. In particular, effector cell frequencies declined rapidly postinfection in favor of relatively larger proportions of central memory cells.