Peripheral blood T-cell signatures from high-resolution immune phenotyping of γδ and αβ T-cells in younger and older subjects in the Berlin Aging Study II

Abstract

Background: Aging and latent infection with Cytomegalovirus (CMV) are thought to be major factors driving the immune system towards immunosenescence, primarily characterized by reduced amounts of naïve T-cells and increased memory T-cells, potentially associated with higher morbidity and mortality. The composition of both major compartments, γδ as well as αβ T-cells, is altered by age and CMV, but detailed knowledge of changes to the γδ subset is currently limited.

Results: Here, we have surveyed a population of 73 younger (23-35 years) and 144 older (62-85 years) individuals drawn from the Berlin Aging Study II, investigating the distribution of detailed differentiation phenotypes of both γδ and αβ T-cells. Correlation of frequencies and absolute counts of the identified phenotypes with age and the presence of CMV revealed a lower abundance of Vδ2-positive and a higher amount of Vδ1-positive cells. We found higher frequencies of late-differentiated and lower frequencies of early-differentiated cells in the Vδ1+ and Vδ1-Vδ2-, but not in the Vδ2+ populations in elderly CMV-seropositive individuals confirming the association of these Vδ2-negative cells with CMV-immunosurveillance. We identified the highest Vδ1:Vδ2 ratios in the CMV-seropositive elderly. The observed increased CD4:CD8 ratios in the elderly were significantly lower in CMV-seropositive individuals, who also possessed a lower naïve and a larger late-differentiated compartment of CD8+ αβ T-cells, reflecting the consensus in the literature.

Conclusions: Our findings illustrate in detail the strong influence of CMV on the abundance and differentiation pattern of γδ T-cells as well as αβ T-cells in older and younger people. Mechanisms responsible for the phenotypic alterations in the γδ T-cell compartment, associated both with the presence of CMV and with age require further clarification.

Keywords: Aging; CMV; Differentiation Phenotypes; Flow Cytometry; Senescence; αβ T-cells; γδ T-cells.

Fig. 1

Detailed distribution of αβ T-cell and γδ T-cell compartments and differentiation phenotypes. Each line reflects frequencies of a single individual, color-coded. Red indicates high values, blue low. The first part of the heat map describes the CD4+ and CD8+ αβ T-cells (blue background) and their differentiation status displayed in columns and characterized by the expression of CD27 (purple), CD28 (turquoise), CD45RA (orange) and CD16 (green), whereas white indicates the absence of the individual markers. The second part of the heat map describes the abundance of the Vδ1+, Vδ2+ and Vδ1-Vδ2- γδ T-cell compartments and their differentiations signatures. The black lines in the coding-table for the differentiation markers show the frequencies of the parental compartments. The heat map is horizontally divided into CMV-seronegatives (CMV-) in the upper and seropositives (CMV+) in the lower part. Both parts are further stratified for subject age

Fig. 2

Phenotypic distribution of the Vδ1+, Vδ2+ and Vδ1-Vδ2- γδ T-cell subsets in young and old CMV seropositive and seronegative individuals. (a) Median frequencies of the three subsets in the total γδ T-cells and (b) in the CD8+ group of γδ T-cells. Detailed differences are shown between young (y) and old (o) CMV-seropositives and seronegatives of Vδ2+ cells (c), Vδ1+ cells (d), Vδ1-Vδ2- cells (e) and the Vδ1:Vδ2 ratio (f). The Mann–Whitney test was used for the statistical comparison. Bonferroni-correction adjusted the significance cutoff to p ≤ 0.0083

Fig. 3

Age and CMV associated differences in the αβ T-cell compartment. (a) Frequencies of αβ T-cells, identified as γδ TCR negative, in young (y) and old (o) CMV seropositive and seronegative individuals. (b) The abundance of CD4+ and (c) of CD8 T-cells. (d) CD4:CD8 ratios. The Mann–Whitney test was used for the statistical comparison. Bonferroni-correction adjusted the significance cutoff to p ≤ 0.0083

Fig. 4

Differentiation-scheme of the entire identified γδ T-cell and αβ T-cell compartments. Each cellular compartment (lines) is represented by a pie-chart for young and old CMV-seropositive (CMV+) and seronegative (CMV-) individuals. The γδ T-cell compartment is shown with a blue background, the αβ T-cells with a white background. The single differentiation statuses are color coded in the pie charts, using green for early- and red for late-differentiated phenotypes