Soluble CD163 made by monocyte/macrophages is a novel marker of HIV activity in early and chronic infection prior to and after anti-retroviral therapy

Abstract

CD163, a monocyte- and macrophage-specific scavenger receptor, is shed during activation as soluble CD163 (sCD163). We have previously demonstrated that monocyte expansion from bone marrow with simian immunodeficiency virus (SIV) infection correlated with plasma sCD163, the rate of AIDS progression, and the severity of macrophage-mediated pathogenesis. Here, we examined sCD163 in human immunodeficiency virus (HIV) infection. sCD163 was elevated in the plasma of individuals with chronic HIV infection (>1 year in duration), compared with HIV-seronegative individuals. With effective antiretroviral therapy (ART), sCD163 levels decreased in parallel with HIV RNA levels but did not return to HIV-seronegative levels, suggesting the presence of residual monocyte/macrophage activation even with plasma viral loads below the limit of detection. In individuals with early HIV infection (≤1 year in duration), effective ART resulted in decreased sCD163 levels that were comparable to levels in HIV-seronegative individuals. sCD163 levels in plasma were positively correlated with the percentage of CD14+CD16+ monocytes and activated CD8+HLA-DR+CD38+ T lymphocytes and were inversely correlated with CD163 expression on CD14+CD16+ monocytes. With ART interruption in subjects with early HIV infection, sCD163 and plasma virus levels spiked but rapidly returned to baseline with reinitiation of ART. This study points to the utility of monocyte- and macrophage-derived sCD163 as a marker of HIV activity that links viral replication with monocyte and macrophage activation. These observations underscore the significance of monocyte and macrophage immune responses with HIV pathogenesis.

Figure 1.

sCD163 levels are significantly increased in plasma during chronic and early human immunodeficiency virus (HIV) infection and are decreased after receipt of antiretroviral therapy (ART). Plasma samples from 30 subjects with chronic HIV infection (Chronic HIV+) and 14 subjects with recent HIV infection (Early HIV+) were examined at 2 time points, as follows: (1) no current ART (Pre-ART) and (2) after 3 months of ART (3mos ART). Samples were compared with samples from 29 age-matched HIV-seronegative individuals (HIV-). Plasma samples were examined for levels of sCD163 (A), interleukin (IL)-10 (B), sCD14 (C), and lipopolysaccharide (D). A, Plasma sCD163 levels were elevated before ART in both Chronic HIV+ and Early HIV+ groups. After 3 months of ART, sCD163 decreased in both Chronic HIV+ and Early HIV+ groups; however, the levels only returned to levels similar to those in uninfected individuals in the Early HIV+ group. The lines show the mean level and standard error of the mean. An analysis of variance (ANOVA) was used to test for variance between groups. If the ANOVA determined that a difference was statistically significant (P < .05), then this was followed by post hoc t tests. For comparisons between Chronic HIV+ Pre-ART and Chronic HIV+ 3mos ART and for comparisons between Early HIV+ Pre-ART and Early HIV+ 3mos ART, matched t tests were used. Three samples from uninfected individuals, 3 Early HIV+ Pre-ART samples, and 8 Early HIV+ 3mos ART samples had values that were below the lower limit of detection of the Limulus Amebocyte Lysate assay.

Figure 2.

Percentage change in plasma viral load and absolute number of CD4+ T lymphocytes correlated with change in plasma sCD163 levels after antiretroviral therapy (ART). To directly measure the effect of ART on virological parameters examined in individuals with chronic human immunodeficiency virus (HIV) infection, the percentage change was calculated ([{value before ART – value after 3 months of ART}/value before ART] ×100%), where a negative percentage represented a decrease and a positive percentage represented an increase after 3 months of ART. The percentage change in sCD163 level was correlated with the percentage change in plasma virus (A) and absolute number of CD4+ T lymphocytes (B). The absolute number of monocytes was correlated to sCD163 levels in plasma samples from subjects with chronic HIV infection prior to ART (C) but not after 3 months of ART (D). r = Spearman's correlation coefficient. P value of ≤ .05 is statistically significant.

Figure 3.

The percentage of CD14+CD16+ monocytes and CD8+HLA-DR+CD38+ T lymphocytes correlates with sCD163. Peripheral blood mononuclear cells (PBMCs) from 8 patients with chronic human immunodeficiency virus (HIV) infection (Chronic HIV+) before antiretroviral therapy (Pre-ART) (closed circles) and 9 patients after 3 months of antiretroviral therapy (3mos ART) (2 sets of samples were from matched patients) as well as PBMCs from all 14 HIV-infected individuals with early infection (Early HIV+) (open circles) obtained Pre-ART and 3mos ART were examined. Flow cytometry analysis was used to determine the percentage of CD14+CD16+ monocytes (A, B), the median fluorescence intensity (MFI) of CD163 on CD14+CD16+ monocytes (C, D), and the percentage of activated CD8+HLA-DR+CD38+ T lymphocytes (E, F) in all PBMC samples. In A, C, and E, nonparametric Mann-Whitney t tests were used where a P value of ≤ .05 is significant. For the Early HIV+ samples, paired t tests were used, because all samples were matched Pre-ART and 3mos ART. In B, D, and F, the correlations were performed with both Early HIV+ samples (open circles) and Chronic HIV+ samples (closed circles). B, the percentage of CD14+CD16+ monocytes significantly correlated to plasma sCD163. D, the expression level of CD163 on CD14+CD16+ monocytes inversely correlated to plasma sCD163. F, the percentage of activated CD8+HLA-DR+CD38+ T lymphocytes significantly correlated to plasma sCD163 level. The r and P values shown are for the overall correlation, including both patients with recent infection and patients with chronic infection. r = Spearman's correlation coefficient, P value of ≤ .05 is significant.

Figure 4.

Plasma viral load and CD8+ T lymphocyte count, but not CD4+ T lymphocyte count, parallel sCD163 levels in plasma, even during antiretroviral therapy (ART) interruption. Plasma samples were examined for sCD163 (red; left axis), plasma viral load (purple; right axis), absolute number of CD8+ T lymphocytes (blue; left axis), and absolute number of CD4+ T lymphocytes (green; left axis). The shaded gray area represents samples from patients receiving ART, and the white area represents samples from patients with no ART. Shown are data for 2 representative individuals (A, B) with early acquired human immunodeficiency virus (HIV) infection of 9 individuals who were examined. Samples were plotted over the first year of infection from date of seroconversion (seroconversion was defined as the day of the first positive Western blot result). Plasma viral load and CD8+ lymphocyte count paralleled sCD163 levels in plasma. Also shown are data for 2 representative individuals (C, D) with early HIV infection of 4 individuals who were examined during periods of ART interruption and reinitiation. sCD163 levels increased during therapy interruption, paralleling plasma viral load and absolute numbers of CD8+ T lymphocytes, and decreased upon reinitiation of ART. CD4+ T lymphocyte counts were not affected by therapy interruption.