Relationship between cytomegalovirus (CMV) IgG serology, detectable CMV DNA in peripheral monocytes, and CMV pp65(495-503)-specific CD8+ T cells in older adults

Abstract

In immunocompetent individuals, cytomegalovirus (CMV) is thought to persist in a latent state in monocytes and myeloid progenitor cells, establishing a lifelong infection. In CMV-seropositive older adults, aging has been associated with both expansion of CMV pp65(495-503)-specific CD8(+) T cell clones and shrinkage of the T cell repertoire that characterize T cell immunosenescence. In fact it has been suggested that chronic CMV infection is a driving force in age-related T cell immunosenescence. In older adults, chronic CMV infection is conventionally diagnosed by positive IgG serology which does not distinguish between past and persistent infections. To better define the relationship between chronic CMV infection and expansion of CMV pp65(495-503)-specific CD8(+) T cells, we directly assessed CMV viral DNA in monocyte-enriched peripheral blood mononuclear cells in 16 HLA-A2-positive elderly volunteers (mean age = 83 years). While all participants had positive CMV IgG serology by enzyme-linked immunosorbent assays, only nine (56%) had detectable CMV DNA by nested polymerase chain reaction. These nine individuals had significantly higher percentages of CMV pp65(495-503) tetramer-positive CD8(+) T cells (median = 1.3%) than those without detectable CMV DNA (median = 0.1%; p < 0.001). Absolute CMV IgG antibody titers did not differ between these two groups (median = 54.6 vs 44.2 EU/ml, respectively, p = 0.4). CMV IgM titers were negative for all 16 participants, suggesting that recent primary CMV infection was unlikely. These results demonstrate a strong association between the presence of CMV DNA in peripheral monocytes and the expansion of CD8(+) T cells specific for the CMV immunodominant epitope pp65(495-503). Although the sample size in this study is relatively small, these findings provide initial evidence suggesting the heterogeneity of CMV IgG-seropositive older adult population and CMV viral DNA detection in peripheral monocytes as an informative tool to better understand the relationship between chronic CMV infection and T cell immunosenescence.

Fig. 1

a CMV viral DNA detection in monocyte-enriched PBMCs from all 16 participants by nested PCR targeted to the CMV UL123 gene. Upper panel: lane 1 positive control, 167-bp PCR product from purified genomic DNA of human CMV strain AD169 CMV_AD169 (Advanced Biotech Inc., Paterson, NJ, USA); lanes 2–3 negative controls with no input sample DNA (lane 2, primers for both rounds of PCR, lane 3, primer for first round only); lanes 4–19 participant samples. Nine participants had detectable CMV viral DNA (top CMV DNA band, lanes 4–12), and seven participants had no detectable CMV DNA (lanes 13–19); lower panel: PCR amplification of GAPDH. b Distribution of serum anti-CMV IgG titers as determined by ELISA (UBI, Mountain View, CA, USA); with a titer of ≥15 EU/ml considered as seropositive, all participants were seropositive. Horizontal bars indicate median values

Fig. 2

a Flow cytometric dot plots from CMV pp65_495–504 tetramer analysis of a representative participant with detectable CMV viral DNA. Left panel: CD4⁺ and CD8⁺ T cells gated on CD3⁺ cells; right panel: tetramer binding to CD8^bright+ (blue or magenta) T cells, but not CD8^dim (green) or CD8⁻ (yellow) T cells. b Distribution of percentages of CD8⁺ T cells that were CMV pp65_495–503 specific in participants with detectable (+) or no detectable (−) CMV DNA in monocyte-enriched PBMCs. Horizontal bars indicate median values