Ageing, defence mechanisms and the immune system.

Of all the systems in the body, the immune system is probably the best understood, both in mechanistic terms and in the ways in which it changes during ageing. Studies of the ageing immune system (immuno gerontology) can be traced back to the early part of this century (and even earlier), and the literature has burgeoned in the last three decades. Perhaps the first publication was of the investigation undertaken by Peter Ludwig Panum (a Danish physician and discoverer of endotoxin) on the outbreak of measles in the Faroes in 1846. The Faroes had been free of measles since the previous epidemic of 1781. The 1846 outbreak affected 75-95% of the population although "of the many aged people still living on the Faroes who had had measles in 1781, not one was attacked a second time" [1]. This experiment of nature seems out of step with traditional thought about ageing and immunity, which views ageing as an immunodeficiency state that predisposes the host to infectious diseases (and possibly neoplasms).