Early depletion of Mycobacterium tuberculosis-specific T helper 1 cell responses after HIV-1 infection

Abstract

Background: The acid-fast bacillus Mycobacterium tuberculosis is often the first manifestation of acquired immunodeficiency syndrome in patients infected with human immunodeficiency virus (HIV). This study was conducted to better understand the mechanism underlying M. tuberculosis-specific pathogenicity early after onset of HIV infection.

Methods: M. tuberculosis-specific T helper 1 (Th1) cells were studied in HIV negative (n=114) and chronically HIV infected (n=68) Tanzanian subjects by using early secreted antigenic target 6 (ESAT6) protein or tuberculin (purified protein derivative) with interferon-gamma ELISPOT and intracellular cytokine staining. In a longitudinal study, the effect of acute HIV infection on M. tuberculosis-specific Th1 cells was determined by polychromatic flow cytometric analysis in 5 subjects with latent M. tuberculosis infection who became infected with HIV.

Results: In tuberculosis (TB)-asymptomatic subjects (i.e., subjects with unknown TB status who did not show clinical signs suggestive of TB), chronic HIV infection was associated with a decreased percentage of subjects with detectable M. tuberculosis-specific Th1 cells (P< .001) a decrease which was not observed among subjects with active TB. Acute HIV infection induced a rapid depletion of M. tuberculosis-specific Th1 cells in 4 subjects remained TB asymptomatic, whereas the population of these cells remained stable in subjects who remained HIV negative (P< .01).

Conclusions: Taken together, these data suggest a mechanism of rapid M. tuberculosis-specific Th1 cell depletion that may contribute to the early onset of TB in individuals with latent M. tuberculosis infection who become HIV infected.

Figure 1. IFNγ responses detected after in vitro stimulation with PPD and recombinant ESAT6 protein are CD4 T cell responses

Shown are representative dot plots from one study participant for the detection of IFNγ (x axis) and activation marker CD69 within the CD4 T cell (left panels) and CD8 T cell (right panels) subsets after 6 hour stimulation of whole blood and intracellular cytokine staining for IFNγ.

Figure 2. Chronic HIV infection is associated with decreased ESAT6- and PPD-specific TH1 cell responses in TB asymptomatic subjects, but not in subjects with pulmonary Tuberculosis

Shown are the SFC/10⁶ PBMC responding to recombinant ESAT6 protein (upper panel) and PPD lower panel for each subject (A), and with the corresponding total CD4 cell counts (x axis) for HIV infected individuals in (B). HIV negative TB asymptomatic subjects (n=110) are shown as blue circles, in HIV negative subjects with pulmonary tuberculosis (n=3) as red circles, in HIV infected TB asymptomatic subjects (n=55) as blue diamonds and HIV positive subjects with pulmonary tuberculosis (n=11) as red diamonds. The cut-off value was 20 SFC/10⁶PBMC (indicated as a red dotted line). Statistical analysis for (A) was performed using the Mann Whitney Test and for (B) the Spearmans-rank test.

Figure 3. A high proportion of MTB-specific TH1 cells express HIV coreceptor CCR5

Shown is the cell surface expression of CCR5 (B) on gated IFNγ positive CD4 T cells detected after 6 hour stimulation with RD1 peptides. (C and D) show the proportion of CCR5⁺CD4 T cells within different CD4 T cell subsets for 9 HIV^-subjects who were latently infected with MTB. Statistical analysis was performed using the Wilcoxon matched pairs test.

Figure 4. Rapid depletion of MTB-specific TH1 cells early during HIV infection

Shown are for each studied HIV seroconverter the frequencies of PPD-specific (upper panel) and Region of difference 1-specific (lower panel) CD4 T cells as percent of memory CD4 T cells. (A) shows representative dot plots after stimulation with ESAT6 and or media alone. (B) shows the MTB-specific memory CD4 T cells detected before and after HIV infection (red arrow) from 5 subjects who became HIV infected. Memory CD4 T cells were determined by CD27 and CD45RO expression. Naïve CD4 T cells (CD27⁺CD45^-) were excluded for analysis of memory CD4 T cells. IFNγ positive memory CD4 T cells were detected after overnight stimulation with Purified Protein Derivative (PPD), Early Secretory Antigenic Target 6 (ESAT6) or Culture Filtrate Protein 10 (CFP10). The background was subtracted.