In Experimental Tuberculosis Infection, the Bacteriostatic Function of Macrophages Is Activated by Th1 CD4⁺...

The pivotal component in the protection against TB is the tissue macrophages (Mф). These cells have been demonstrated to play a crucial role in the elimination of pathogens and mycobacterial killing. Elucidation of the molecular and phenotypic events that determine the outcome of infection in Mф is fundamental to understanding the key features of these cells that are so important in fighting infection. Mф activation is driven by cytokines and other inflammatory mediators secreted by T lymphocytes. The interaction between Mycobacterium tuberculosis (Mtb) and host Мф has been the subject of extensive in vitro research. This dynamic interplay represents a pivotal step in the progression of mycobacterial infection because pulmonary macrophages constitute the primary line of defense against the pathogen, thereby serving as the initial immune cells to which Mtb must adapt to establish a replicative foothold within the host. Our studies have demonstrated that highly differentiated Th1 effectors with the CD27^low phenotype exhibit superior efficacy in activating both peritoneal (Mф: T cell ratio ranging from 125:1 to 625:1) and pulmonary macrophages (Mф: T cell ratio = 5:1) compared to cells with the CD27^high phenotype. Furthermore, our findings indicate that this activation mechanism is not contingent upon the production of reactive nitrogen species. To effectively activate the bacteriostatic function of macrophages, CD27^high T lymphocytes must differentiate into effectors with the CD27^low phenotype.