Varicella-Zoster Virus-Specific Cell-Mediated Immune Response Kinetics and Latent Viral Load Depending on Aging

Abstract

Herpes zoster (HZ), an infection caused by varicella-zoster virus (VZV) reactivation, results from an age-related decline in VZV-specific cell-mediated immunity (CMI). Digital droplet PCR (ddPCR) precisely quantifies latent VZV DNA in the blood, a potential biomarker of subclinical viral reactivation and its association with HZ risk. This study assessed VZV-specific CMI, latent viral burden, and humoral immunity in healthy adults according to age. We prospectively enrolled healthy adults aged between 40 and 80 years between February and April 2024. VZV-specific CMI was quantified using interferon-gamma enzyme-linked immunosorbent spot assay, latent VZV DNA in peripheral blood mononuclear cells using ddPCR, and VZV-specific IgG using enzyme-linked immunosorbent assay. VZV-specific CMI declined significantly from age 40 (r = -0.356, p = 0.001). Latent VZV burden increased from age 50 (r = 0.459, p < 0.001). VZV-specific antibody levels showed no significant association with age (r = 0.004, p = 0.967). VZV-specific T cell responses were lower in ddPCR-positive compared with ddPCR-negative individuals (p = 0.095), although the difference was not statistically significant. VZV-specific CMI declined from age 40, while latent viral load increased from age 50. Our findings suggest that ddPCR-based quantification of latent VZV DNA may serve as a biomarker of subclinical viral reactivation, potentially informing HZ risk stratification and vaccination strategies. Further studies are required to validate the predictive value of ddPCR in identifying individuals at high risk of developing HZ.

Keywords: Varicella‐zoster virus; aging; cell‐mediated immunity; digital droplet PCR; herpes zoster; latent VZV burden.

Figure 1

Age‐related change in VZV‐specific T‐cell responses measured by ELISPOT assay. (A) Distribution of VZV‐specific T‐cell responses across age groups (40 s, 50 s, 60 s, and 70 s; n = 20 for each group). Peripheral blood mononuclear cells (PBMCs) were stimulated with VZV lysate, and interferon‐γ‐producing cells were quantified using ELISPOT assay. Results are presented as spot‐forming units (SFU) per 1,000,000 PBMCs. Boxes indicate interquartile ranges; horizontal lines indicate medians; whiskers represent minimum and maximum values. (B) Correlation between age and VZV‐specific T‐cell responses in the overall cohort (ages 40–79 years, n = 80). Spearman's rank correlation showed a significant negative correlation (r = −0.356, p = 0.001). (C) Distribution of VZV‐specific T‐cell responses across age groups excluding participants in their 40 s (n = 60). Assay methods and visualization are as described in panel A. (D) Correlation between age and VZV‐specific T‐cell responses excluding individuals in their 40 s (n = 60). Spearman's rank correlation indicated a consistent inverse trend (r = −0.342, p = 0.008).

Figure 2

Age‐associated change in latent VZV DNA load in peripheral blood mononuclear cells (PBMCs). (A) Distribution of latent VZV DNA levels across age groups (40 s, 50 s, 60 s, and 70 s; n = 20 for each group). Genomic DNA was extracted from PBMCs and analyzed using digital droplet PCR (ddPCR) targeting VZV ORF63. Results are expressed as VZV copies per 100,000 PBMCs. The boxplots display medians (horizontal line), interquartile ranges (boxes), and full ranges (whiskers). (B) Correlation between age and latent VZV DNA levels in the overall cohort (n = 80). Spearman's rank correlation showed no significant association (r = 0.154, p = 0.172). (C) Distribution of latent VZV DNA levels excluding participants in their 40 s (n = 60). Methods and visualization are as described in panel A. (D) Significant positive correlation between age and latent VZV DNA levels in participants aged 50 years and older (n = 60), as determined by Spearman's rank correlation (r = 0.459, p < 0.001).

Figure 3

Distribution and age‐related trend of VZV‐specific IgG antibody titers in healthy adults. (A) Distribution of VZV‐specific IgG antibody titers across age groups (40 s, 50 s, 60 s, and 70 s; n = 20 for each group). Serum samples were tested using a commercial enzyme‐linked immunosorbent assay (ELISA), and results are expressed in IU/mL. Boxplots indicate the median, interquartile range, and total range (whiskers). (B) Correlation between age and VZV‐specific IgG titers in the overall cohort (n = 80). Spearman's rank correlation showed no significant relationship (r = 0.009, p = 0.939). (C) Distribution of VZV‐specific IgG antibody titers in participants aged ≥ 50 years (n = 60). Visualization and analysis are as described in panel A. (D) Correlation between age and IgG antibody titers among participants aged ≥ 50 years.). Spearman's rank correlation showed no significant relationship (r = –0.197, p = 0.131).