Lower cellular immune responses to influenza A (H3N2) in the elderly

Influenza epidemic is an important cause of severe illness in the elderly. Age-dependent morbidity of influenza in the elderly is associated with weakened immunity. The baseline age-related memory T cell activity in Chinese persons who are exposed to influenza virus through natural infection, are associated with the protective response to the virus after vaccination, thus providing important pre-vaccination information. A cohort from the general population was established at the end of an influenza season in an area where influenza occurs regularly, and followed for 24 weeks. The subjects had no vaccination history for 5 years. Memory T cell responses were evaluated using a set of peptides spanning the influenza A (H3N2) entire proteome in a gamma interferon (IFN-gamma)-enzyme-linked immunospot (ELISPOT) assay, prior to the next influenza season. Changes of hemagglutination inhibition (HI) antibody titers were also evaluated. IFN-gamma(+) T cell responses against influenza peptides were significantly lower in subjects of 60 years and older. Although the age-related decline of cellular immune response was clear, no significant association of antibody titers with age was found. The pre-vaccination baseline of memory IFN-gamma(+) T cell immunity state in elderly Chinese was significantly lower than in people younger than 60 years. Measurement of the ex vivo cellular immune responses to influenza should be incorporated into the evaluation of protective immunity in elderly persons.