Increased Neutrophil Count and Decreased Neutrophil CD15 Expression Correlate With TB Disease Severity and Treatment Response Irrespective of HIV Co-infection

Abstract

Tuberculosis remains a leading cause of death globally despite curative treatment, partly due to the difficulty of identifying patients who will not respond to therapy. Simple host biomarkers that correlate with response to drug treatment would facilitate improvement in outcomes and the evaluation of novel therapies. In a prospective longitudinal cohort study, we evaluated neutrophil count and phenotype at baseline, as well as during TB treatment in 79 patients [50 (63%) HIV-positive] with microbiologically confirmed drug susceptible TB undergoing standard treatment. At time of diagnosis, blood neutrophils were highly expanded and surface expression of the neutrophil marker CD15 greatly reduced compared to controls. Both measures changed rapidly with the commencement of drug treatment and returned to levels seen in healthy control by treatment completion. Additionally, at the time of diagnosis, high neutrophil count, and low CD15 expression was associated with higher sputum bacterial load and more severe lung damage on chest x-ray, two clinically relevant markers of disease severity. Furthermore, CD15 expression level at diagnosis was associated with TB culture conversion after 2 months of therapy (OR: 0.14, 95% CI: 0.02, 0.89), a standard measure of early TB treatment success. Importantly, our data was not significantly impacted by HIV co-infection. These data suggest that blood neutrophil metrics could potentially be exploited to develop a simple and rapid test to help determine TB disease severity, monitor drug treatment response, and identify subjects at diagnosis who may respond poorly to treatment.

Keywords: blood neutrophil count; neutrophil phenotype; tuberculosis biomarker; tuberculosis disease severity; tuberculosis treatment outcome.

Figure 1

Baseline neutrophil blood counts and phenotypic changes in active TB disease. (A–C) Box plots of (A) baseline neutrophil blood count (PMN count), (B) PMN/Lymphocyte ratios, and (C) Surface CD15 expression levels of TB cases (n = 79), Xpert-positive/culture-negative controls (n = 15), and healthy controls (HC; n = 23), Data represents median values and was analyzed using Kruskal-Wallis test for Dunn's multiple comparisons. (D–H) Spearman's rank correlation analysis of neutrophil blood counts and CD15 expression with bacterial burden and chest X-ray score.

Figure 2

Longitudinal measurement of blood neutrophil count and CD15 expression during anti-TB treatment. Changes in neutrophil blood count (PMN), PMN/Lymphocyte ratio and surface CD15 expression levels over the course of treatment in TB cases (A–C) and Xpert-positive/culture-negative controls (D–F). P-values were obtained using the Wilcoxon rank sum test and Kruskal-Wallis tests for Dunn's multiple comparisons. Dotted line represents the median healthy control levels.

Figure 3

Impact of pre-treatment characteristics on rate of culture conversion. (A–D) Baseline neutrophil blood (PMN) count, CD15 expression, bacterial load, and chest X-ray scores were retrospectively separated into four groups based on time to MGIT culture negativity. Early responders became and remained culture negative within the 1st month, medium responders by 2 months, and slow responders by month 6 post-treatment initiation. In this analysis treatment failure are individuals who were culture positive at all time points. P-values were obtained using the Mann-Whitney test.