Performance of Interferon-Gamma and IP-10 Release Assays for Diagnosing Latent Tuberculosis Infections in Patients with Concurrent Malaria in Tanzania

Abstract

Interferon-gamma (IFN-γ) release assays (IGRAs) are used to detect cellular immune recognition of Mycobacterium tuberculosis The chemokine IFN-γ-inducible protein 10 (IP-10) is an alternative diagnostic biomarker to IFN-γ. Several conditions interfere with IGRA test performance. We aimed to assess the possible influence of Plasmodium falciparum infection on the IGRA test QuantiFERON-TB GOLD® In-Tube (QFT) test and an in-house IP-10 release assay. In total, 241 Tanzanian adults were included; 184 patients with uncomplicated malaria (88 human immunodeficiency virus [HIV] coinfected) and 57 HIV-infected patients without malaria infection. Malaria was treated with artemether-lumefantrine (Coartem®). QFT testing was performed before initiation of malaria treatment and at days 7 and 42. In total, 172 patients completed follow-up. IFN-γ and IP-10 was measured in QFT supernatants. We found that during malaria infection IFN-γ and IP-10 levels in the unstimulated samples were elevated, mitogen responsiveness was impaired, and CD4 cell counts were decreased. These alterations reverted after malaria treatment. Concurrent malaria infection did not affect QFT test results, whereas there were more indeterminate IP-10 results during acute malaria infection. We suggest that IGRA and IP-10 release assay results of malaria patients should be interpreted with caution and that testing preferably should be postponed until after malaria treatment.

Figure 1.

Box-and-whiskers plot (Tukey) showing cytokine levels at enrollment (day 0). P values reflect comparison of the malaria groups to the non-malaria-HIV-infected group (Mann–Whitney U). The antigen levels depend on the Mycobacterium tuberculosis exposure of the group, whereas the nil and mitogen response reflect the patients' immune status. HIV = human immunodeficiency virus; ns = not significant. The Quantiferon test has an upper detection limit at 10 IU/mL. In general, we found higher nil levels and lower response to mitogen stimulation in the malaria-infected groups compared with the non-malaria-HIV-infected group.

Figure 2.

Box-and-whiskers plot (Tukey) showing cytokine levels at enrollment (day 0) of unstimulated (nil) and mitogen-stimulated samples of the malaria patients stratified by parasite densities. Cytokine levels were compared using Kruskal–Wallis test. HIV = human immunodeficiency virus; Pf = Plasmodium falciparum. N = 29, 30, and 35 for the malaria-HIV-infected group, and N = 29, 30, and 25 for the malaria-non-HIV group. The Quantiferon test has an upper detection limit at 10 IU/mL. In general, we found higher nil levels and lower mitogen responses in patients with high parasite levels.

Figure 3.

Box-and-whiskers plot (Tukey) showing cytokine levels during follow-up at day 0, 7, and 42. Only patients with complete follow-up and no malaria reinfections were included for this analysis. Malaria-HIV-infected group N = 67, malaria-non-HIV-group N = 51, and non-malaria-HIV-group N = 49, P values reflect comparison to levels at inclusion (day 0), Wilcoxon signed-rank test. HIV = human immunodeficiency virus; ns = not significant. The Quantiferon test has an upper detection limit at 10 IU/mL. In general, we found a reduction in nil levels for all study groups and an increase in antigen and mitogen responses in the malaria groups during the follow-up.