Age-dependent immune profile in healthy individuals: an original study, systematic review and meta-analysis.

Background: The circulatory peripheral immune system is the most convenient approach for determining an individual's immune status. Due to various reasons, while previous studies have addressed the critical impact of age, most individual studies did not analyze immunosenescence in a systemic manner, which complicates the possibility of building a reference range for age-dependent immune profiles for effective immune monitoring. To address this gap, this study analyzed a group of healthy individuals to establish age-specific reference ranges of the healthy circulatory immune profile, and a systematic review and meta-analysis were conducted to validate the findings and create generalizable immune cell reference ranges.

Results: Our study recruited a total of 363 healthy Taiwanese adults (median age 42 years [IQR 30, 62], age range 21 to 87 years, 43.3% male), including 158 under 40 years old, 127 between 40-64 years old, and 78 over 64 years old. Significant age-related alterations were observed in both adaptive and innate immune cell subsets. CD8 + T cells decreased and CD4/CD8 ratio increased, with notable increases in NK cells. CD4 + T cells were less impacted by aging, while CD8 + T cells significantly lost CD28 and increased CD31 expression with age. A clear reverse trend in naïve and memory subsets of CD4 + and CD8 + T cells was observed. Detailed reference ranges for immune cell subsets in healthy Taiwanese adults were established. A systematic review included 7,425 adults and a meta-analysis of 12 eligible studies confirmed our findings in Taiwan, enhancing generalizability.

Conclusions: Combined with previous studies and original data through a systematic review and meta-analysis, we highlighted and quantified significant immune profile differences between older and younger individuals. The sex and age-specific reference ranges for peripheral immune cell subsets can serve as a basis for effective immune monitoring of various aging-related illnesses.