Attenuation of toll-like receptor expression and function in latent tuberculosis by coexistent filarial infection with restoration following antifilarial chemotherapy

Abstract

Mycobacterium tuberculosis (Mtb) and filarial coinfection is highly prevalent, and the presence of filarial infections may regulate the Toll-like receptor (TLR)-dependent immune response needed to control Mtb infection. By analyzing the baseline and mycobacterial antigen-stimulated expression of TLR1, 2, 4, and 9 (in individuals with latent tuberculosis [TB] with or without filarial infection), we were able to demonstrate that filarial infection, coincident with Mtb, significantly diminishes both baseline and Mtb antigen-specific TLR2 and TLR9 expression. In addition, pro-inflammatory cytokine responses to TLR2 and 9 ligands are significantly diminished in filaria/TB-coinfected individuals. Definitive treatment of lymphatic filariasis significantly restores the pro-inflammatory cytokine responses in individuals with latent TB. Coincident filarial infection exerted a profound inhibitory effect on protective mycobacteria-specific TLR-mediated immune responses in latent tuberculosis and suggests a novel mechanism by which concomitant filarial infections predispose to the development of active tuberculosis in humans.

Figure 1. Filarial infection is associated with decreased expression of TLR2 and TLR9 at baseline and following PPD and CFP stimulation in latent TB patients.

PBMC from PPD⁺Fil⁻ (n = 9) and PPD⁺Fil⁺ (n = 9) patients were examined at baseline (A) or stimulated with PPD (B) or Mtb CFP (C) or TT (D) for 24 hours, and TLR1, 2, 4, and 9 mRNA levels were measured by real-time RT-PCR. Results are shown as relative expression at baseline (A) or fold change over media control (B, C, and D). p values were calculated using the Mann-Whitney test.

Figure 2. Filarial infection is associated with diminished cytokine responses to TLR2 and TLR9 ligands in latent TB patients.

PBMC from PPD⁺Fil⁻ (n = 9) and PPD⁺Fil⁺ (n = 9) patients were stimulated with TLR2 ligand (Pam3Cys) (A) or TLR9 ligand (ODN) (B) or TLR4 ligand (LPS) (C) for 24 hours, and IL-1β, TNF-α, IL-6, IL-12p70, and IFN-γ cytokine levels were measured by ELISA. Results are shown as net cytokine production over media control. P values were calculated using the Mann-Whitney test.

Figure 3. Treatment of filarial infection is associated with significantly enhanced cytokine responses to TLR2 and TLR9 ligands in latent TB patients.

PBMC from PPD⁺Fil⁺ (n = 9) patients, pre and post treatment, were stimulated with ligands for TLR2 (Pam3Cys) (A), TLR9 (ODN) (B), or TLR4 (LPS) (C) for 24 hours, and IL-1β, TNF-α, IL-6, IL-12p70, and IFN-γ cytokine levels were measured. Results are shown as net cytokine production over media control. P values were calculated using the Wilcoxon signed rank test. (D) The correlation between the decrease in circulating filarial antigen levels and the increase in TNF-α and IFN-γ levels in patients with both lymphatic filariasis and latent TB following antifilarial treatment. P values were calculated using the Spearman rank test.