Adipokines as New Biomarkers of Immune Recovery: Apelin Receptor, RBP4 and ZAG Are Related to CD4+ T-Cell Reconstitution in PLHIV on Suppressive Antiretroviral Therapy

Abstract

A significant proportion of people living with HIV (PLHIV) who successfully achieve virological suppression fail to recover CD4⁺ T-cell counts. Since adipose tissue has been discovered as a key immune organ, this study aimed to assess the role of adipokines in the HIV immunodiscordant response. This is a multicenter prospective study including 221 PLHIV starting the first antiretroviral therapy (ART) and classified according to baseline CD4⁺ T-cell counts/µL (controls > 200 cells/µL and cases ≤ 200 cells/µL). Immune failure recovery was considered when cases did not reach more than 250 CD4⁺ T cells/µL at 144 weeks (immunological nonresponders, INR). Circulating adipokine concentrations were longitudinally measured using enzyme-linked immunosorbent assays. At baseline, apelin receptor (APLNR) and zinc-alpha-2-glycoprotein (ZAG) concentrations were significantly lower in INRs than in immunological responders (p = 0.043 and p = 0.034), and they remained lower during all ART follow-up visits (p = 0.044 and p = 0.028 for APLNR, p = 0.038 and p = 0.010 for ZAG, at 48 and 144 weeks, respectively). ZAG levels positively correlated with retinol-binding protein 4 (RBP4) levels (p < 0.01), and low circulating RBP4 concentrations were related to a low CD4⁺ T-cell gain (p = 0.018 and p = 0.039 at 48 and 144 weeks, respectively). Multiple regression adjusted for clinical variables and adipokine concentrations confirmed both low APLNR and RBP4 as independent predictors for CD4⁺ T cells at 144 weeks (p < 0.001). In conclusion, low APLNR and RBP4 concentrations were associated with poor immune recovery in treated PLHIV and could be considered predictive biomarkers of a discordant immunological response.

Keywords: HIV; adipokines; antiretroviral therapy; immunodiscordant response; poor immune recovery.

Figure 1

Study design. (A) Flow chart illustrating patient selection and enrolment. HIV-infected subjects were included and categorized as controls and cases according to the baseline ART threshold of 200 CD4⁺ T cell counts. Cases were categorized according to their immune status after 144 weeks of follow-up in “immunological recoverers” (IRs) or “immunological nonrecoverers” (INRs) depending on the threshold of CD4⁺ T cell counts of 250 CD4⁺ T cell counts/µL. (B) CD4 ⁺ T cell and CD8⁺ T cell count, and CD4/CD8 ratio in controls, IRs, and INRs during the study follow-up. * indicates significant differences at 144 w compared to baseline values using the Wilcoxon test. ● indicates significant differences compared to controls, and Ø indicates significant differences between INRs and IRs at each point of time, by nonparametric Mann–Whitney test.

Figure 2

Circulating adipokine concentrations before initiating ART. (A) Baseline concentrations of adiponectin, omentin, APLNR, and ZAG in controls (n = 120), IRs (n = 77), and INRs (n = 22). p-value indicates significant differences among indicated groups by nonparametric Mann–Whitney test. (B) Heatmap showing the correlation analyses between all adipokines evaluated and clinical characteristics at baseline. Correlation matrix is color-coded according to the Spearman (ρ) correlation coefficient (−1:1, red: blue through white), and correlations with statistically significance are indicated. (C) Network interactions generated with the set of the four differentially expressed biomarkers at baseline (adiponectin, apelin receptor, omentin, and ZAG) identified by the STRING database. The STRING database identified different biological processes associated with our network using the false discovery rate (FDR). Adiponectin = ADIPOQ, apelin receptor = APLNR, omentin = ITLN1 and zinc-alpha-2-glycoprotein = ZAG.

Figure 3

Follow-up circulating adipokine concentrations. Circulating apelin, APJ, omentin, and ZAG concentrations at (A) 48 weeks and (B) 144 weeks after ART in cases (IRs (n = 77) and INRs (n = 22)) compared to controls (n = 120). p-value indicates significant differences among groups by nonparametric Mann–Whitney test.

Figure 4

Validation cohort using CD4⁺ T-cell count gain as a marker of immune recovery. (A) Flow chart illustrating cases (n = 101) categorized according to CD4⁺ T-cell count gain after 144 weeks of ART initiation instead of 250 cell/µL CD4⁺ T-cell count cut-off: A group for those who gained ≥ 100 cells/µL, and B group for those who gained < 100 cells/µL. (B) Circulating ZAG, RBP4, and APLNR concentrations at baseline (B,C) at 144 weeks of ART. p-value indicates significant differences among indicated groups by nonparametric Mann–Whitney test.

Figure 5

ART effect on circulating adipokine concentrations. Longitudinal study of circulating FABP4, ZAG, omentin, and resistin concentrations during ART follow-up. * indicates significant differences at 144 w compared to baseline values using the Wilcoxon test. ● indicates significant differences compared to controls (n = 120), ▲ indicates significant differences between controls and IR, and Ø indicates significant differences between INRs (n = 22) and IRs (n = 77) at each point of time, by nonparametric Mann–Whitney test.

Figure 6

Adipokine concentrations in different ART schemes. (A) Circulating adipokine concentrations affected by the 2 NRTIs + PI scheme (n = 91) at 48 weeks. (B) Circulating adipokine concentrations affected by the 2 NRTIs + NNRTI scheme (n = 109) at 48 weeks (resistin) and 144 weeks (apelin). NNRTI + PI group included 8 patients. * indicates significant differences between ART schemes by nonparametric Kruskal–Wallis test.