Molecular and cellular basis of immunosenescence.

Aged persons and most animals studied show a significant decline in the immune response primarily caused by changes in the T cell compartment. This decline in T cell function is due to a combination of factors: decreased production of new naive T cells by the involuting thymus; extensive antigen-induced activation leading to replicative senescence and clonal exhaustion of certain T cells; and postmitotic aging of resting T cells, a phenomenon also observed in other non-dividing cells such as neurons or muscle cells. The relative importance of these processes in the T cell defective immune response observed in aged humans and animals remains to be established although it is very likely that all of them participate in immunosenescence. The cellular, molecular biological basis and the clinical consequences of the defective immune response in aging were extensively discussed and reviewed at the 5th EUCAMBIS meeting. This paper summarizes the main presentations at the meeting. This special issue contains selected presentations from the congress, in the form of peer-reviewed full papers and the abstracts of two papers previously published in the journal.