Valdiglesias V, et al. - Researchers assessed the interaction between the age-related decline of the immune response and the upregulation of the inflammatory response by investigating the role of different inflammatory mediators on frailty status in the elderly (aged ≥ 65 years). Study participants (n=180) were classified according to Fried's frailty phenotype. They analyzed plasma concentrations of neopterin, tryptophan, kynurenine, phenylalanine, tyrosine as well as kynurenine/tryptophan (Kyn/Trp) and phenylalanine/tyrosine (Phe/Tyr) ratios as immune stimulation biomarkers. They also measured nitrite and C-reactive protein levels as indicators of nitric oxide production and acute inflammation, respectively. Frailty status was identified to be strongly correlated with four parameters—neopterin, tryptophan, nitrite, and C-reactive protein—although multiple regression analysis confirmed the role of nitrite only as a predictor, supporting its use as a potential biomarker of frailty.