Phenotypically resembling myeloid derived suppressor cells are increased in children with HIV and exposed/infected with Mycobacterium tuberculosis

Abstract

Increased disease susceptibility during early life has been linked to immune immaturity, regulatory T-cell/TH2 immune biasing and hyporesponsiveness. The contribution of myeloid derived suppressor cells (MDSCs) remains uninvestigated. Here, we assessed peripheral MDSC in HIV-infected and -uninfected children with tuberculosis (TB) disease before, during and after TB treatment, along with matched household contacts (HHCs), HIV-exposed, -infected and -uninfected children without recent TB exposure. Serum analytes and enzymes associated with MDSC accumulation/activation/function were measured by colorimetric- and fluorescence arrays. Peripheral frequencies of cells phenotypically resembling MDSCs were significantly increased in HIV-exposed uninfected (HEU) and M.tb-infected children, but peaked in children with TB disease and remained high following treatment. MDSC in HIV-infected (HI) children were similar to unexposed uninfected controls; however, HAART-mediated MDSC restoration to control levels could not be disregarded. Increased MDSC frequencies in HHC coincided with enhanced indoleamine-pyrrole-2,3-dioxygenase (IDO), whereas increased MDSC in TB cases were linked to heightened IDO and arginase-1. Increased MDSC were paralleled by reduced plasma IP-10 and thrombospondin-2 levels in HEU and significantly increased plasma IL-6 in HI HHC. Current investigations into MDSC-targeted treatment strategies, together with functional analyses of MDSCs, could endorse these cells as novel innate immune regulatory mechanism of infant HIV/TB susceptibility.

Keywords: Children; Early life immunity; HIV exposure; Myeloid derived suppressor cells (MDSCs); Tuberculosis.

Figure 1

Higher frequencies of circulating infant MDSC upon HIV exposure and TB infection/disease. (A-D) MDSCs presented as a frequency of total peripheral blood mononuclear cells in (A) QFN negative controls without HIV exposure (n = 20), with HIV infection (n = 23) and HIV exposure uninfected (n = 37); Longitudinal assessments in M.tb infected HHC with (n = 11) and without (n = 22) HIV infection, and TB patients with (n=7) and without ( n = 14) HIV infection at (B) baseline, (C) month 3 and (D) month 6 time points. Each data point represents a single biological sample and the horizontal line in each box represents the median, whiskers = 1.5 interquartile range (IQR) with points beyond 1.5IQR plotted individually. *P≤0.05; ** P ≤0.01;*** P ≤0.001; ns = nonsignificant. Individual samples from each group were evaluated independently.

Figure 2

Higher frequencies of circulating infant M-MDSC upon HIV exposure and TB infection/disease. Frequencies of CD14+ M-MDSCs in QFN negative controls without HIV exposure (n = 20), with HIV infection (n= 23) and HIV exposure uninfected (n = 37); M.tb infected HHC with (n=11) and without (n = 22) HIV infection, and TB patients with (n = 7) and without (n=14) HIV infection. The horizontal line in each box represents the median, whiskers = 1.5 interquartile range (IQR) with points beyond 1.5IQR plotted individually. *P≤0.05; ** P ≤0.01;***P ≤0.001; ns = nonsignificant. Individual samples from each group were evaluated independently.

Figure 3

Ex-vivo levels of MDSC-associated plasma analytes during M.tb infection and/or HIV infection, exposure and disease. Multiplex cytokine concentrations (pg/mL) of IP-10, G-CSF, M-CSF, IL-6, sCD40 and Thrombospondin-2 from QFN negative controls without HIV exposure (n = 10), with HIV infection (n=10) and HIV exposure uninfected (n = 10); Longitudinal assessments in M.tb infected HHC with (n = 10) and without (n = 10) HIV infection, and TB patients without (n = 9) HIV infection at baseline and month 6 time points. The horizontal line represents the median and whiskers the standard error. Due to multiple comparisons, letters a-d were used to indicate statistical significance, where values with the same letter are not statistically different from each other. P≤0.05 were considered statistically significant. Individual samples from each group were evaluated independently.

Figure 4

Comparisons of arginase activity (U/L) in ex-vivo plasma of QFN negative controls without HIV exposure (n = 10), with HIV infection (n = 10) and HIV exposure uninfected (n = 10); Longitudinal assessments in M.tb infected HHC with (n = 10) and without (n = 10) HIV infection, and TB patients without (n = 9) HIV infection at baseline and month 6 time points. The horizontal line in each box represents the median, whiskers = 1.5 interquartile range (IQR). *P≤0.05; ** P ≤0.01;***P ≤0.001; ns = nonsignificant. Individual samples from each group were evaluated independently.

Figure 5

Comparisons of IDO concentrations (ng/ml) in ex-vivo plasma of QFN negative controls without HIV exposure (n = 10), with HIV infection (n = 10) and HIV exposure uninfected (n = 10); Longitudinal assessments in M.tb infected HHC with (n = 10) and without (n = 10) HIV infection, and TB patients without (n = 9) HIV infection at baseline and month 6 time points. The horizontal line in each box represents the median, whiskers = 1.5 interquartile range (IQR) with points beyond 1.5IQR plotted individually. *P≤0.05; ** P ≤0.01;***P ≤0.001; ns = nonsignificant. Individual samples from each group were evaluated independently.

Figure 6

Gating strategy employed to define (A) LIN-1- HLA-DR-/low CD11b+CD33high total MDSCs and the (B) HLA-DR-/low CD14+CD11b+CD33high M-MDSCs and HLA-DR-/low CD15+CD11b+CD33high G-MDSCs subsets. The gating strategy plots are from single experiment.