IP-10 measured by Dry Plasma Spots as biomarker for therapy responses in Mycobacterium Tuberculosis infection

Abstract

Tuberculosis (TB) has huge impact on human morbidity and mortality and biomarkers to support rapid TB diagnosis and ensure treatment initiation and cure are needed, especially in regions with high prevalence of multi-drug resistant TB. Soluble interferon gamma inducible protein 10 (IP-10) analyzed from dry plasma spots (DPS) has potential as an immunodiagnostic marker in TB infection. We analyzed IP-10 levels in plasma directly and extracted from DPS in parallel by ELISA from 34 clinically well characterized patients with TB disease before and throughout 24 weeks of effective anti-TB chemotherapy. We detected a significant decline of IP-10 levels in both plasma and DPS already after two weeks of therapy with good correlation between the tests. This was observed both in pulmonary and extrapulmonary TB. In conclusion, plasma IP-10 may serve as an early biomarker for anti-TB chemotherapy responses and the IP-10 DPS method has potential to be developed into a point-of care test for use in resource-limited settings. Further studies must be performed to validate the use of IP-10 DPS in TB high endemic countries.

Figure 1. Dynamics of IP-10 in plasma and Dry Plasma Spots (DPS) during anti-TB chemotherapy.

IP-10 levels measured in plasma and DPS in patients with active TB during 24 weeks of effective anti-TB chemotherapy: Baseline (week 0) (N = 34), week 2 (N = 34), week 8 (N = 28), week 24 (N = 34). Box-whisker plots with median, interquartile ranges and min/max values indicated. P-values were calculated by Wilcoxon Signed Ranks test. A significance level of 0.05 was used.

Figure 2. Comparison of Plasma and Dry Plasma Spots (DPS) IP-10 in Individual patients during anti-TB chemotherapy.

IP-10 levels during 24 weeks of effective anti-TB chemotherapy in (A) plasma and (B) DPS in patients with active TB (N = 34): Baseline (week 0) (N = 34), week 2 (N = 34), week 8 (N = 28), week 24 (N = 34). ¹Patient with pulmonary TB, previously treated (2 years earlier), but responding to present therapy with negative culture, ²Patient with Crohn's disease diagnosed during TB treatment, ³Patient with paradoxical reaction of glandular TB during treatment, ⁴Patient with disseminated TB and exacerbation of known Crohn's disease from week 2.

Figure 3. Correlation between IP-10 levels measured in plasma and Dry Plasma Spots (DPS).

Correlation between plasma samples and DPS for all TB patients at all time-points during treatment (baseline, 2, 8 and 24 weeks). Correlation coefficients were calculated by Spearman's rho (significant values at the 0.01 level, 2-tailed).

Figure 4. IP-10 levels in clinical TB subgroups during anti-TB chemotherapy.

Plasma IP-10 and Dry Plasma Spots (DPS) IP-10 during 24 weeks of anti-TB chemotherapy in (A) extrapulmonary TB (EPTB, N = 14, white box) and pulmonary TB (PTB, N = 14, hatched box), (B) patients with “low symptom score” (N = 16, white box) and “high symptom score” (N = 18, hatched box) and (C) Erythrocyte Sedimentation Rate (ESR) < 40 (N = 16, white box) and >40 (N = 16, hatched box). Box-whisker plots with median, interquartile range and min/max values indicated. P-values were calculated by Mann-Whitney U test. A significance level of 0.05 was used.