Figure 1.

Concept of a less effective allospecific but augmented unspecific immune response in the elderly. (a) T cell subsets in the healthy individuals. (b) Old CD4⁺ T cell with diminished alloresponse potential, including an impaired IL-2 capacity and CD28 downregulation coincide with an increasing NK cell receptor equipment [30,52–54]. (c) Enhanced cytotoxic capacity of old CD28⁻ CD8⁺ T cells that upregulate CD57 while co-expressing NK cell receptors [43,44].