RESUMO
Most studies on natural killer (NK) cells and aging have focused on overall cell numbers and global cytotoxic activity. NK cell functions are controlled by surface receptors belonging to three major families: killer cell immunoglobulin-like receptors (KIRs), natural cytotoxicity receptors (NCRs), and C-type lectins. The expression of these receptors was investigated from childhood through old age in T, NKT- and NK cells and also in the CD56(dim) (cytotoxic) and CD56(bright) (responsible for cytokine production) NK cell subsets. A decrease in the expression of activating receptors (NKp30 and NKp46) was observed in NK cells in elderly individuals. KIR expression was increased only in the CD56(bright) subset. Children presented similar results regarding expression of NKp30 and KIR, but not NKp46. NKG2D expression was decreased in T cells of elderly subjects. Analysis of KIR genotype revealed that KIR2DL5 and KIR2DS3 were significantly associated with old age. Cytotoxic activity was preserved from childhood through old age, suggesting that the increase of the absolute number of CD56(dim), observed in elderly, may represent a compensatory mechanism for the receptor expression alterations. This initial study provides the framework for more focused studies of this subject, which are necessary to determine whether the changing balance of NK receptor expression may influence susceptibility to infectious, inflammatory, and neoplastic diseases.
