IFNG and type 1 diabetes mellitus: Although the precise pathophysiological mechanism underlying the effect of DM as a predisposing risk factor for TB remains unknown, hypotheses that have been suggested included depressed cellular immunity, dysfunction of alveolar macrophages, low levels of interferon gamma, pulmonary microangiopathy, and micronutrient deficiency.18 An animal study shows that rats with T1DM are highly susceptible to M tuberculosis infection.