Effect of hyperglycemia on lung microbiota and treatment outcome in pulmonary tuberculosis: A scoping review

The comorbidity due to pulmonary tuberculosis (TB) and diabetes mellitus (DM) is a global health problem, but its mechanism remains unclear. It is suspected that hyperglycemic alteration of the immune response to TB and the composition of the lung microbiota play an important role. This scoping review aimed to contribute to the understanding of the mechanisms by mapping evidence on the effect of hyperglycemia on physical health indicators, immune cell counts, cytokine levels, and the composition of lung microbiota in patients with the DM-TB comorbidity. A systematic search for research articles about the relationship between hyperglycemia and physical health, immune cells, and cytokine levels in humans was conducted in MEDLINE, Scopus, and CINAHL Plus. Then, articles on the interactions between the immune cells, cytokines, and lung microbiota were identified through Google Scholar and Google search engines. Characteristics of the studies focusing on effects of hyperglycemia, the findings of the articles relevant to the research objectives, and strengths and weaknesses of the selected articles were charted in a data extraction tool. Twenty-one articles on the effects of hyperglycemia on immune mediators and health outcomes of patients with DM-TB were included. The evidence showed hyperglycemia to be associated with unfavorable treatment outcomes; altered counts and functioning of dendritic cells, monocytes, and CD4+ T cells; and changes in cytokine levels (mainly INF-γ, IL-17, IL-1β, IL-2, IL-6, IL-10, and TNF-α) in patients with DM-TB. The composition of the lung microbiota changed in correlation with changes in physical health outcomes, counts of immune cells, and cytokine levels. Thus, hyperglycemia, immune responses, and dysbiosis of the lung microbiota are integral in the pathogenesis of DM-TB and TB treatment outcomes. A prospective cohort study, especially in individuals with newly diagnosed DM versus known DM and concomitant latent TB versus active TB, is recommended to define causal relationships.