Immunity to influenza: the challenges of protecting an aging population.

Influenza viruses cause annual epidemics and occasional pandemics of acute respiratory disease. Improved vaccines that can overcome the decline in immune function with aging and/or can induce broader immunity to novel pandemic strains are a high priority. To design improved vaccines for the elderly, we need to better understand the effects of age on both innate and adaptive immunity. In a murine model, we have determined that defects in antigen-presenting cell (APC) expression of pattern-recognition molecules, co-stimulatory molecules, and cytokine production may play an important role in the reduced clonal expansion of T cells in aging. The use of immunomodulators such as adjuvants may overcome some of the defects of aging immunity and may also be useful in the development of improved vaccines for avian influenza A subtypes that pose a pandemic threat. Several novel strategies including the use of ISCOM-formulated vaccines, mucosal delivery, or DNA vaccination provided cross-subtype protection that could provide an important component of immunity in the event of a pandemic.