In-depth human immune cellular profiling from newborn to frail.

Immune functional decline and remodeling accompany aging and frailty. It is still largely unknown how changes in the immune cellular composition differentiate healthy individuals from those who become frail at a relatively early age. Our aim in this exploratory study was to investigate immunological changes from newborn to frailty and the association between health statute and various immune cell subtypes. The participants analyzed in this study covered human cord blood cells and peripheral blood cells collected from young adults and healthy and frail old individuals. A total of 30 immune cell subsets were performed by flow cytometry based on the surface markers of immune cells. Furthermore, frailty was investigated for its relations with various leukocyte subpopulations. Frail individuals exhibited a higher CD4/CD8 ratio; a higher proportion of CD4+ central memory T cells, CD8+ effector memory T cells, CD27- switched memory B (BSM) cells, CD27+ BSM cells, age-associated B cells, and CD38-CD24- B cells; and a lower proportion of naïve CD8+ T cells and progenitor B cells. The frailty index score was found to be associated with naïve T cells, CD4/CD8 ratio, age-associated B cells, CD27- BSM cells, and CD4+ central memory T cells. Our findings conducted a relatively comprehensive and extensive atlas of age- and frailty-related changes in peripheral leukocyte subpopulations from newborn to frailty. The immune phenotypes identified in this study can contribute to a deeper understanding of immunosenescence in frailty and may provide a rationale for future interventions and diagnosis.