Age-related changes in Type 1 and Type 2 cytokine production in humans.

Although aging is accompanied by several changes in immune function, altered T cell function represents the most consistent and dramatic change. Since cytokines modulate the immune response, it has been postulated that these age-associated changes in T cell function may be due to alterations in cytokine production. Data from murine studies generally support an age-related shift from a Th1-like (IL-2, IFN-gamma) to a Th2-like (IL-4, IL-6, IL-10) cytokine response; however, whether or not such an age-related shift to a Type 2 cytokine response occurs in humans is not certain. This review of over 60 studies in humans, in which Type 1 and Type 2 cytokines were evaluated either alone or together, suggests that age-associated changes in cytokine production are inconsistent. Further, these age-associated changes in cytokine production do not always induce a shift to a Type 2 cytokine response. Importantly, these studies highlight that the stimulus used to induce cytokines influences both the level and pattern of immune response. Additional comprehensive evaluations in human studies are both critical and necessary to clearly identify the impact of altered cytokine production on age-related changes in immune function.