Altered Toll-Like Receptor-4 Response to Lipopolysaccharides in Infants Exposed to HIV-1 and Its Preventive Therapy

Abstract

Pathogen sensing and recognition through pattern recognition receptors, and subsequent production of pro-inflammatory cytokines, is the cornerstone of the innate immune system. Despite the fact that HIV-exposed uninfected (HEU) infants are prone to serious bacterial infections, no study has focused on the functionality of their bacteria recognition system. This is the first study to investigate baseline levels of three critically important immune response molecules in this population: complement component (C)-3, toll-like receptor (TLR)-4, and C-reactive protein (CRP). We enrolled 16 HEU and 6 HIV-unexposed (HU) infants. TLR4 function was investigated by stimulating whole blood with increasing concentrations of TLR4-agonist ultrapure lipopolysaccharides. TLR4/TLR4-agonist dose response were assessed by measuring IL-6 secretion. Complement C3 and CRP were measured by photo spectrometry. Data showed no significant differences in baseline concentration of CRP between HEU and HU infants. Complement C3 was significantly higher in HEU infants than HU infants. TLR4 anergy was observed in 7 of 12 HEU infants, whereas the rest of HEU infants (n = 4) and the control HU infants tested (n = 3) showed responsive TLR4. None of the HEU infants investigated in this study had severe infections in the year after their birth. In conclusion, TLR4 anergy can occur in HEU infants without necessarily translating to increased vulnerability to infectious diseases.

Keywords: C-reactive protein; HIV-1; complement component-3; infants; toll-like receptor-4.

Figure 1

Circulating levels of C3 complement (A) and C-reactive protein (CRP) (B) in whole blood from HIV-exposed and HIV-unexposed (HU) infants. C3 complement and CRP were measured in infants’ serum samples. The difference between HIV-exposed and HU infants was analyzed using the Mann–Whitney U-test. The differences were considered significant for a p-value <0.05. In the figures, bars indicate medians and ranges.

Figure 2

Regression analysis of toll-like receptor (TLR)-4/ultrapure lipopolysaccharides (LPS) dose–response of HIV-exposed uninfected (HEU) infants and HIV-unexposed infants (C). Whole blood from individual participant was stimulated at increasing concentration of LPS (from 0, 0.001 to 1,000 ng), and IL-6 was measured. The slope indicator measures the rise over the run for a linear regression. The p-value simply tests whether the slope is exactly 0 or ≠0. The coefficient of determination means that R² × 100% of the variation in IL-6 can be explained by linear relationship with TLR4-agonist stimulation. (*) Only the one point deviated significantly from 0 (corresponding to the top LPS stimulation).