Cellular immune responses to influenza.

Cellular immune responses are believed to play an important role in controlling influenza infection. CD4+ and CD8+ T cell responses are well described and CD8+ immunity is of paramount importance in killing virally infected cells. In the past few years several novel techniques have been devised which allow quantification of antigen-specific cellular immune responses and these will be reviewed briefly. Influenza-specific cellular immunity is elicited following natural infection and several viral proteins have been identified as targets for cellular responses. Cellular immunity is detectable throughout life in most donors but there is clear evidence of impaired cellular immunity in the elderly, a population at particular risk of influenza infection. This finding must be viewed against the background of 'immune senescence' that is documented with aging. Cellular responses are able to provide heterosubtypic immunity to influenza viral antigens. As such the induction of cellular immune responses is a highly desirable aim of vaccination protocols. Induction of cellular immunity with conventional formalin-inactivated vaccine is poor although some improvement may be derived from novel forms of vaccine delivery such as the use of adjuvanted carriers. Nevertheless, a range of new vaccines is being developed which are more effective in priming cellular responses. Although there is relatively little detail on the nature of the cellular response induced by these agents, they hold out the promise of more effective and durable protection from influenza infection.