IFNG and tuberculosis: An alternative approach to evaluating the intensity of the T-cell response is the measurement of interferon-gamma (IFNγ) concentration using Interferon-Gamma Release Assay (IGRA)—a tool already well established and successfully used, e.g., in the diagnostics of tuberculosis, introduced in a new version for SARS-CoV-2 research (SARS-CoV-2 IGRA version) [44].