As they get older, many older people, mostly men, are fond of saying something along the lines of, “I feel like a 25-year-old.”
As it turns out, judging by the reaction strength of their immune system to an unknown, but harmless, protein antigen, it’s possible for men over 70 to mount an immune response similar to that produced by much younger men -- if they get regular moderate physical activity of about six hours a week.
Previous studies show that the aging immune system suffers from a progressive decrease in function that can lead to several negative situations including increased risk of infectious disease and ineffective response to vaccination. It’s been shown that regular moderate cardiovascular exercise such as walking or cycling may offset some of the immune function decline in healthy older people. However most earlier studies tested the effect of exercise on immune function using in vitro measures of immunity, which aren’t always predictive of in vivo responses. Furthermore many earlier studies depended on antigenic challenges that weren’t novel to the subjects, which stimulated secondary or tertiary responses.
Researchers at the University of Colorado-Boulder wanted to test the popularly accepted notion that people who maintain a physically active lifestyle will enjoy the benefits a stronger immune system into older age. They designed a novel in vivo challenge to the immune system. To get clean, comprehensive results, they used KLH (keyhole limpet hemocyanin), a benign T cell-dependent protein isolate that has been used extensively with animals in the past, that also is safe for humans.
The study, entitled “Influence of age and physical activity on the primary in vivo antibody and T cell-mediated responses in men,” appears in the August 2004 issue of the Journal of Applied Physiology, one of 14 peer-reviewed journals published by the American Physiological Society.
The investigative team was lead by Monika Fleshner and included Taro P. Smith and Sarah L. Kennedy, all from the Department of Integrative Physiology, University of Colorado at Boulder.
The researchers tested almost 50 healthy, young (20-35 years of age) and older (60-79) men, some physically active and some sedentary. Using KLH overcame a major problem in many earlier age vs. exercise studies which typically utilized in vitro tests or vaccine or recall antigens to elicit an immune response. In the first stage, all subjects were “immunized” with KLH with blood collected on day one and then each week for a month. The samples were comprehensively tested by ELISA (enzyme-linked immunoabsorbent assay) for anti-KLH IgM, IgG, IgG1 and IgG2.
The second phase was three weeks later. Subjects received an intradermal injection, or skin test, of KLH with inflammation measured each day for five days to assess anti-KLH delayed-type hypersensitivity response (DTH). There was significant reduction in all anti-KLH measures with aging except for anti-KLH IgG2. The physically active older group had significantly higher anti-KLH IgM, IgG, IgG1 and DTH but not IgG2 compared with the sedentary older group.
Experiment one found that the anti-KLH IgM and IgG titers were elevated three weeks after immunization, showing that the ELISA successfully detected KLH-specific Ig and that KLH immunization induced a primary antibody response. Moreover, the KLH skin test resulted in a DTH reaction that peaked after two days, persisting up to five days. Non-immunized subjects had no inflammation, showing that the DTH reaction was specific to KLH recognition.