Aging and CMV discordance are associated with increased immune diversity between monozygotic twins

Abstract

Background: Broadly, much of variance in immune system phenotype has been linked to the influence of non-heritable factors rather than genetics. In particular, two non-heritable factors: aging and human cytolomegavirus (CMV) infection, have been known to account for significant inter-individual immune variance. However, many specific relationships between them and immune composition remain unclear, especially between individuals over narrower age ranges. Further exploration of these relationships may be useful for informing personalized intervention development.

Results: To address this need, we evaluated 41 different cell type frequencies by mass cytometry and identified their relationships with aging and CMV seropositivity. Analyses were done using 60 healthy individuals, including 23 monozygotic twin pairs, categorized into young (12-31 years) and middle-aged (42-59 years). Aging and CMV discordance were associated with increased immune diversity between monozygotic twins overall, and particularly strongly in various T cell populations. Notably, we identified 17 and 11 cell subset frequencies as relatively influenced and uninfluenced by non-heritable factors, respectively, with results that largely matched those from studies on older-aged cohorts. Next, CD4+ T cell frequency was shown to diverge with age in twins, but with lower slope than in demographically similar non-twins, suggesting that much inter-individual variance in this cell type can be attributed to interactions between genetic and environmental factors. Several cell frequencies previously associated with memory inflation, such as CD27- CD8+ T cells and CD161+ CD4+ T cells, were positively correlated with CMV seropositivity, supporting findings that CMV infection may incur rapid aging of the immune system.

Conclusions: Our study confirms previous findings that aging, even within a relatively small age range and by mid-adulthood, and CMV seropositivity, both contribute significantly to inter-individual immune diversity. Notably, we identify several key immune cell subsets that vary considerably with aging, as well as others associated with memory inflation which correlate with CMV seropositivity.

Keywords: Aging; Cytomegalovirus; Human immunology; Mass cytometry (CyTOF); Monozygotic twins.

Fig. 1

Spearman’s rank correlation (medians of random repeats; see methods) of cell frequencies for young (n = 14 pairs) vs. middle-aged (n = 9 pairs) twins. Each dot represents one cell type, colored by the significance of that correlation in the younger and middle-aged twin pairs. Black dots denote if no significant correlation was found in either young or middle-aged twins. The thick black line represents values at which the young and middle-aged twins have the exact same Spearman’s rank correlation. The upper and lower thin gray lines represent boundaries 0.1 above and below the thick black line

Fig. 2

Euclidean distances between twins and between demographically similar non-twins (matched CMV status to twin and within +/− 5 years of age) over age. Each dot represents a pairwise distance for the twins or the median of the pairwise distance of repeated random matching of demographically similar non-twins, over (a) all cell subset frequencies, (b) CD4+ T cells, or (c) CD8+ T cells. 95% confidence intervals are shown by the shaded areas around the lines of best fit

Fig. 3

Spearman’s rank correlation plot of cell frequencies for CMV concordant negative (n = 8, medians of random repeats reported; see methods) vs. CMV discordant (n = 5) twins. Each dot represents one cell type. The thick black line represents values at which both CMV −/+ and −/− twins have the exact same Spearman’s rank correlation. The upper and lower thin gray lines represent boundaries 0.1 above and below the thick black line

Fig. 4

Euclidean distance for all cell subset frequencies between twin and demographically similar non-twin pairs (median distance for 6 repeated random matching of demographically similar individuals), stratified by pairwise CMV seropositivity. Each dot represents the immunological distance, taking into account all cell frequencies, between a twin or non-twin pairing. P values by Wilcoxon rank sum tests

Fig. 5

Cell frequencies significantly correlated with CMV positivity in our cohort. Each row in the forest plot represents a cell subset for which the frequency was found to be significantly correlated (FDR-adjusted P value < 0.05) with CMV positivity within the cohort (after adjustment for age, sex and twin pair (or singlet) origin). The log odds ratio using the features of interest to predict CMV positivity are also shown as measurements of effect size, along with corresponding confidence intervals