Mycobacterial Growth Inhibition Assay (MGIA) as a Host Directed Diagnostic Tool for the Evaluation of the Immune Response in Subjects Living With Type 2 Diabetes Mellitus

Abstract

The lack of efficient and cost-effective diagnostic tools contributes to poor control of tuberculosis in endemic countries. Moreover, host biological processes influence susceptibility, and infection resolution. It is well known that comorbidities such as type 2 diabetes mellitus (DM2) affect the host immune response, making individuals more susceptible to Mycobacterium tuberculosis infection. Currently, there are no laboratory tools that can identify those subjects who have a higher risk of developing the disease. In this study, we used a whole blood mycobacterial growth inhibition assay to assess the immune response capacity to inhibit mycobacterial growth between healthy subjects and those living with DM2 with optimal and poor glycemic control. We also measured cytokine levels in the culture supernatant by cytokine bead arrays. We included 89 patients with DM2: 54 patients with optimal control (mean age 56.2 ± 11.75 years) and 35 patients with poor control (mean age 52.05 ± 9.94 years). We also included 44 healthy subjects as controls (mean age 42.12 ± 11.75 years). We compared the Δlog UFC (a value that represents the difference between mycobacterial growth in the control tube versus the subject’s blood) between each group. Our results demonstrate that patients with DM2 had a lower capacity to inhibit M. tuberculosis growth (Δlog UFC DM2 subjects 0.9581 (-0.3897 to 2.495) vs Δlog UFC healthy subjects 0.7190 (-0.2678 to 2.098); p=0.013). Comparing subjects living with DM2 (optimal and poor glycemic control) vs healthy subjects, we found only significant differences between healthy subjects and patients poorly controlled (Δlog UFC optimal control group 0.876 (-0.3897 to 2.495); Δlog UFC poor control group 1.078 (0.068 to 2.33); Δlog UFC healthy subjects 0.7190 (-0.2678 to 2.098); p= 0.022). Therefore, glycemic control assessed by glycosylated hemoglobin values influences the capacity of the host to control the infection. Our results confirm that the whole blood mycobacterial growth inhibition assay has potential utility as an in vitro marker of M. tuberculosis immunological control in vivo in subjects living with DM2. This assay can be used to evaluate the immune response of each individual against M. tuberculosis, allowing clinicians to choose a more specific host-directed therapy.

Development and application of the direct mycobacterial growth inhibition assay: a systematic review

“…applied the direct whole blood MGIA to evaluate the immune response in patients with type-2 diabetes mellitus (DM2) with optimal and poor glycaemic control ( 99 ). They found significantly reduced control of M.tb H37Rv growth among DM2 patients compared with healthy volunteers, and among DM2 patients with poor glycaemic control (but not those with optimal glycaemic control) compared with healthy volunteers ( 99 ). This is consistent with the well-documented increased risk of TB in DM2 patients, particularly those with poor glycaemic control.…”

“…This is consistent with the well-documented increased risk of TB in DM2 patients, particularly those with poor glycaemic control. The authors point to the potential utility of the direct whole blood MGIA as an in vitro marker of M.tb control in vivo in DM2 patients, and as a tool for evaluating individual mycobacteria-specific immune responses to inform host-directed therapy selection ( 99 ). Kewcharoenwong et al.…”

The association between type 2 diabetes and pulmonary cavitation revealed among IGRA-positive tuberculosis patients

“…Furthermore, using a model of in vitro granulomas generated by DM2 patients' peripheral blood mononuclear cells infected with M. bovis BCG, the authors observed that PBMCs from GSH-supplemented patients produced enhanced levels of IFN-γ and controlled bacterial replication more efficiently than those from placebo-treated patients ( 30 ). In particular, the levels of IFN-γ were markedly reduced in samples from patients with poor glycemic control, which also failed to inhibit bacterial growth ( 31 ). Thus, the different immune responses involved in IFN-γ between TB with DM and without DM may be due not only to differences in the frequencies of innate and adaptive immune cells but also to uncontrolled hyperglycaemia.…”