Interferon-gamma (IFN-gamma) levels finally become stable with increasing age as revealed by using an ELISA corresponding to the bioactivity

The immune status is a parameter of the capacity of the immune system to fe nd off microorganisms. The use of leukocyte subtyping to define the immune status is clinically established. IFN-gamma is a key cytokine directing the immune response. In this study, we investigated whether IFN-gamma is a mor e sensitive parameter of the immune status. All persons tested showed stabl e quantities of white blood cell counts over the whole study. Analyses of t he lymphocyte subpopulations of two time points resulted in a strong correl ation with high statistical significance for the percentage of CD3, CD4, CD 8, CD19, CD45 -subtypes and CD56/16 positive cells. IFN-gamma production by the individuals correlates between these time points also, but only if an ELISA strongly correlating to IFN-gamma bioactivity was used instead of oth er commercial IFN-gamma ELISAs. The IFN-gamma production by males was less variable than by females. Furthermore, intraindividual differences in IFN-g amma secretion were minimal after the age of 46. In conclusion, our data de monstrate that IFN-gamma is a more sensitive parameter for the actual statu s of the immune system, since its titer shows alterations faster than leuko cyte subtyping. Furthermore, leukocyte subtypes do not correspond to the pr oduction capacity of the regulatory cytokine IFN-gamma in healthy individua ls. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.