Fig. 1

Protective versus pathological role of IFNγ⁺CD4⁺ T cells during Mycobacterium tuberculosis (Mtb) infection. Mtb exposure in most young children and immunodeficient people evokes a hypoactive IFNγ⁺CD4⁺ T cell response, which is inefficient in containing the bacilli. Therefore, Mtb infection in these people results in primary TB, frequently affecting the extrapulmonary sites. In contrast, most of the immunocompetent adults mount a balanced immune response to Mtb and contain it in the form of latent TB. With the course of time, IFNγ⁺CD4⁺ T cell response would aggravate in nearly 10% of latently infected people, leading to the development of active TB in them. Similar aggravation of IFNγ⁺CD4⁺ T cells is to blame for TB–IRIS development in a subset of ART-treated, HIV- and Mtb-coinfected people