Immune correlates of Mycobacterium Tuberculosis patients in Zambia stratified by HIV serostatus and level of immunity-a cross-sectional analytical laboratory based study

Abstract

Background

People living with HIV (PLHIV) co-infected with tuberculosis (TB) have a distinct clinical presentation and poorer treatment outcomes compared to HIV-seronegative TB patients. Excluding low CD4 count, innate immune factors associated with TB are not fully elucidated. We, therefore, characterised and compared the expression of IL-6, TNF-α, IFN-γ, and IL-10 in whole blood of treatment naïve TB patients stimulated with heat-killed Mycobacterium tuberculosis stratified by HIV status and the level of CD4 count.

Results

We recruited 39 HIV seropositive and 31 HIV seronegative TB patients. Median (IQR) age was 35(28–42) years and 31(25–36) years respectively, and a majority had pulmonary tuberculosis i.e. 38(95%) and 30(97%), respectively. The two groups were significantly different in the distribution of CD4 count, 563 [465–702.5 cells/mm3] vs 345 [157–483 cell/mm3] in HIV negative vs HIV positive respectively p = <0.001. Post stimulation, the expression of IL-6 in HIV negative TB patients was significantly higher than in the HIV positive 16,757366 [8,827–23,686 pg/ml] vs. 9,508 [5,514–15,008 pg/ml], respectively; p = 0.0360. TNF-α and IFN-γ were highly expressed in HIV negative TB patients compared to the HIV positive though not statistically significant. We only observed higher expression of IL-6 in HIV negative patients in comparison to the HIV positive when stratified by level of CD4 counts as < 500 and ≥ 500 cell/mm ³ for both cohorts. 21,953 [8,990–24,206 pg/ml] vs 9,505 [5,400–15,313 pg/ml], p value = 0.0585 in patients with CD4 count < 500 cell/mm ³ and 13,168 [7,087–22,584 pg/ml] vs 10,413 [7,397–14,806 pg/ml], p value = 0.3744 for patients with CD4 count of ≥ 500 cell/mm3 respectively. We found a positive pairwise correlation between TNF-α -alpha and IL-6 in both HIV positive and HIV negative patients, r = 0.61 (95% CI 0.36–0.72; p < 0.0001) and r = 0.48 (95% CI 0.15–0.68; p = 0.005) respectively. The IFNγ/IL-10 ratio was higher in HIV negative when compared to HIV positive individuals, 0.052 [0.0–0.28] vs 0.007 [0–0.32] respectively; p = 0.05759. IL-6 independently reduced the probability of TB/HIV, Adjusted odds ratio 0.99, p value 0.007.

Conclusions

This study suggests that HIV seronegative TB patients have a higher pro-inflammatory response to MTB than HIV seropositive TB patients. Further, it also shows that the level of CD4 influences immunomodulation. The findings suggest that the difference in cytokine expression may be responsible for the distinct patterns of TB presentation between HIV positive and HIV negative patient.