AGE-RELATED-CHANGES IN IMMUNE REACTIVITY - THE INFLUENCE OF INTRINSICDEFECTS AND OF A CHANGED COMPOSITION OF THE CD4-CELL COMPARTMENT( T)

Aging is accompanied by a decline in immune reactivity which to a majo r extent can be attributed to changes at the level of the regulatory C D4+ T cells. In addition to evidence pointing to intrinsic defects, re sulting in improper responsiveness of lymphocytes, it is likely that m any age-related phenomena can be explained by a changed composition of the T cell compartment. Most likely as a consequence of thymic involu tion, the fraction of naive T cells in the periphery decreases, result ing in poor responses to neoantigens in particular. Moreover, due to a ntigenic exposure the fraction of memory cells increases. It is likely that, regardless of their phenotype, cells from aged individuals are subject to intrinsic defects or to immunosuppression, resulting in a l ower responsiveness. As far as CD4+ T cells are concerned, recent stud ies have demonstrated that naive and memory cells behave differently w ith regard to activation requirements and lymphokine production. Age-r elated changes in T cell reactivity will be discussed in the context o f these observations.