Elevated humoral response to cytomegalovirus in HIV-infected individuals with poor CD4+ T-cell immune recovery

Abstract

Some HIV-infected c-ART-suppressed individuals show incomplete CD4+ T-cell recovery, abnormal T-cell activation and higher mortality. One potential source of immune activation could be coinfection with cytomegalovirus (CMV). IgG and IgM levels, immune activation, inflammation and T-cell death in c-ART-suppressed individuals with CD4+ T-cell counts >350 cells/μL (immunoconcordant, n = 133) or <350 cells/μL (immunodiscordant, n = 95) were analyzed to evaluate the effect of CMV humoral response on immune recovery. In total, 27 HIV-uninfected individuals were included as controls. In addition, the presence of CMV IgM antibodies was retrospectively analyzed in 58 immunoconcordant individuals and 66 immunodiscordant individuals. Increased CMV IgG levels were observed in individuals with poor immune reconstitution (p = 0.0002). Increased CMV IgG responses were significantly correlated with lower nadir and absolute CD4+ T-cell counts. In contrast, CMV IgG responses were positively correlated with activation (HLA-DR+) and death markers in CD4+ T-cells and activated memory CD8+ T-cells (CD45RA-CD38+). Longitudinal subanalysis revealed an increased frequency of IgM+ samples in individuals with poor CD4+ T-cell recovery, and an association was observed between retrospective IgM positivity and the current level of IgG. The magnitude of the humoral immune response to CMV is associated with nadir CD4+ T-cell counts, inflammation, immune activation and CD4+ T-cell death, thus suggesting that CMV infection may be a relevant driving force in the increased morbidity/mortality observed in HIV+ individuals with poor CD4+ T-cell recovery.

Fig 1. CMV IgG levels in the study participants.

The IgG level was determined in plasma samples from healthy HIV-uninfected individuals (blue dots), HIV-positive individuals (orange dots), immunoconcordant individuals (green dots) and immunodiscordant individuals (red dots). The boxes represent the median and interquartile range of the values. Individual data of all subjects is displayed. The median values were compared using a non-parametric Mann-Whitney U-test. P-values have been corrected for multiple testing using Holm’s method.

Fig 2. Correlations between CMV IgG antibody levels, immunological variables and T-cell destruction.

A) Correlations between IgG levels and nadir CD4 T-cell counts, absolute CD4⁺ and CD8⁺ T-cell counts. B) Correlations between IgG levels and activation markers (measured as the percentage of HLADR and CD38) in CD4⁺ and CD8⁺ T-cells and in memory CD4⁺ and CD8⁺ T-cells (measured as the percentage of CD38) and the inflammatory marker sCD14. C) Correlations between IgG levels and the expression of the pro-apoptotic marker CD95 and total cell death in CD4⁺ and CD8⁺ T-cell populations. Total cell death was evaluated in 24-h ex vivo PBMC cultures. Linear correlation (Spearman) r and FDR-adjusted p-values are shown.

Fig 3. Pattern of CMV reactivation (IgM⁺/high-avidity IgG) in HIV-infected individuals.

Evolution of HIV viral load (VL, blue lines) and CD4 T-cell counts (green lines) during HIV infection in immunoconcordant (A) and immunodiscordant (B) subjects is presented. Samples in which IgM antibodies were measured are indicated (closed arrowheads). Solid red lines represent IgM-positive/high-avidity IgG samples. Periods of no highly active antiretroviral therapy (pre-HAART period, grey areas) or without treatment (orange areas) are also depicted. Areas without color indicate that individuals were under HAART.

Fig 4. Association between CMV reactivation and CMV IgG antibody levels and T-cell death.

Plasma CMV IgM antibody and IgG avidity was determined. Subjects with at least one IgM-positive/high-avidity IgG sample were classified as IgM-positive (IgM⁺) individuals (individuals with reactivations). Subjects in whom IgM was not detected are shown as IgM-negative (IgM^-) individuals. The relationship between CMV reactivation and IgG levels (A) and total cell death (B) is shown. All HIV⁺ individuals (orange dots) and immunoconcordant (green dots) and immunodiscordant (red dots) subgroups are represented. The boxes represent the median and interquartile range of the values. Individual data of all subjects is displayed. The median values were compared using a non-parametric Mann-Whitney U-test. P-values have been corrected for multiple testing using Holm’s method.