Cytokine polymorphisms, immunosenescence and neurodegeneration

The influence of genetics on immunosenescence (age-associated immune deficiency) remains to be resolved. Common genetic variation (polymorphism) that resides within the genes encoding cytokines is an important regulator to positively or negatively affect immunosenescence. Cytokines regulate the type and magnitude of the immune function. Polymorphism can influence the expression level of the cytokine transcript, and thus potentially its corresponding protein, which can subsequently cause an imbalance in the cytokine cascade.

Herein we examine the current literature with respect to cytokine polymorphisms in aging and the age-related neurodegenerative disorder, Parkinson’s disease. Aging studies have identified two cytokine promoter polymorphisms that have shown associations: IL-6 (−174) and IL-10 (−1082). However, other groups have failed to confirm these associations, due in part to studies of limited sample sizes examining a restricted number of cytokine polymorphisms. The inflammatory processes that characterize the cell death that is the hallmark of neurodegenerative disorders such as Parkinson’s disease may also be influenced by cytokine polymorphisms. As with aging, the results to date have been inconsistent, although a number of studies have suggested IL-1β (−511) and TNF-α (−308) show significant association with Parkinson’s disease susceptibility.

Given the complexity of the cytokine network, and the dynamic interplay between anti- and pro-inflammatory aspects, cross-sectional studies examining many cytokine variants in large sample series are now warranted. Genome-wide association studies and the use of whole-exome and whole-genome sequencing strategies may hold promise in elucidating the role of cytokine polymorphisms in the inflammatory processes in both age-related disease and aging.