If the immune system is chronically stressed, such as by organ transplants or HIV infection, then it ages noticeably faster - in effect the immune system wears down with overuse like a burdened machine. You might look on this sort of outcome as a much faster burn through the normal process of immune system use and degeneration with age, and it has consequences in terms of health and life expectancy. For example:
The University of Cambridge research team investigated whether the chronic immune stress of liver disease and organ transplantation accelerates aging of the immune system, which in turn contributes to excess morbidity and mortality in established liver graft recipients. Study leader Dr. Graeme Alexander explains, "There is a marked increase in the prevalence of cardiac disease, malignancy, cerebrovascular disease and infections in patients with established liver grafts, affecting a majority of cases eventually and which in the past have been attributed to agents used to suppress immune responses. However, an alternative (and not exclusive) hypothesis is that liver transplant recipients develop premature immune senescence which is also associated with these same pathologies, perhaps consequent to chronic [immune system activation]."
During aging, a reduction in T-cell renewal, together with a progressive enrichment of terminally differentiated T cells, translates into a general decline of the immune system, gradually leading to immunosenescence. ... Constant stimulation of the immune system by HIV or due to co-infections activates the innate and adaptive immune system, resulting in release of mediators of inflammation. Immune activation coupled with lack of anti-inflammatory responses likely results in accelerated aging in HIV disease.
The accelerated immune system aging experienced by those who suffer HIV infection is well known, and an area of ongoing medical research. It's quite possible that some of the strategies being developed by the AIDS research community to address this issue could be adapted to rejuvenate aspects of a normally age-damaged immune system. You might look to these posts and articles, for example:
- AIDS-Damaged Immune Systems and Aging Immune Systems
- Telomerase to Fix Immune System Aging
- Reprogramming an Exhausted Immune System
Desai S, & Landay A (2010). Early immune senescence in HIV disease. Current HIV/AIDS reports, 7 (1), 4-10 PMID: 20425052