Interleukin-6 Production Does Not Increase With Age

Investigators have reported an increase, decrease, or no effect of age on interleukin-6 (IL-6) production. Differences in experimental conditions and the health status of subjects may explain these contradicting results. Because the subjects used in most of the previous studies were not carefully screened for health, we investigated the effect of age on IL-6 production in healthy young and elderly subjects. Twenty young (aged 20-30 years) and 26 elderly (>65 years) men completed the study. Each subject was screened for good health, undergoing physical examinations and laboratory tests. Circulating IL-6 levels were not significantly different between young and elderly subjects. A subgroup of subjects representing both young and elderly volunteers had high (>1000 pg/ml) circulating levels of IL-6. However, circulating IL-6 levels were low (<100 pg/ml) in the majority of subjects in both age groups. Peripheral blood mononuclear cells (PBMC) were cultured for IL-6 production in the presence or absence of phytohemagglutinin (PHA) or concanavalin (Con)A for 48 hours. Unstimulated secretion of IL-6 by PBMC cultured in autologous plasma (AP) or fetal bovine serum (FBS) was detectable in the majority of cultures. Age did not influence this spontaneous secretion of IL-6. PBMC stimulation with PHA or ConA significantly increased IL-6 production, but age did not affect the ability of PBMC to secrete IL-6 after stimulation when cultured in FBS. IL-6 production by PBMC cultured in AP and stimulated with PHA was not affected by age. However, when stimulated with ConA, PBMC from the elderly subjects produced less IL-6 than PBMC from the young subjects. Because IL-6 has been suggested to contribute to the age-related increase in prostaglandin (PG)E2 and nitric oxide (NO) production, we investigated the effect of age on the production of IL-6 by murine peritoneal macrophages (Mphi) as well as the effect of IL-6 on the production of other Mphi inflammatory products. Similar to the findings in humans, mouse age did not influence the level of IL-6 produced by Mphi. These data suggest that in healthy subjects, increased production of IL-6 is not a normal consequence of aging. Previously reported higher IL-6 levels in elderly subjects might reflect an underlying, undiagnosed disease state. PGE2 and NO production were not affected by the addition of IL-6 to Mphi from young mice or anti-IL-6 antibody to Mphi from old mice. Thus, IL-6 does not appear to influence the Mphi production of selected inflammatory molecules.