Fil: Basile, Juan I. Academia Nacional de Medicina. Instituto de Investigaciones Hematológicas Mariano R. Castex; Argentina.Fil: Geffner, Laura J. Academia Nacional de Medicina. Instituto de Investigaciones Hematológicas Mariano R. Castex; Argentina.Fil: Romero, María M. Academia Nacional de Medicina. Instituto de Investigaciones Hematológicas Mariano R. Castex; Argentina.Fil: Balboa, Luciana. Academia Nacional de Medicina. Instituto de Investigaciones Hematológicas Mariano R. Castex; Argentina.Fil: Sabio y García, Carmen. Academia Nacional de Medicina. Instituto de Investigaciones Hematológicas Mariano R. Castex; Argentina.Fil: Ritacco, Viviana. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas; Argentina.Fil: García, Ana. Hospital Muñíz. Instituto de Tisioneumonologías; Argentina.Fil: Cuffré, Mónica. Hospital Muñíz. Instituto de Tisioneumonologías; Argentina.Fil: Abbate, Eduardo. Hospital Muñíz. Instituto de Tisioneumonologías; Argentina.Fil: López, Beatriz. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas; Argentina.Fil: Barrera, Lucía. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas; Argentina.Fil: Ambroggi, Marta. Hospital Muñíz. Instituto de Tisioneumonologías; Argentina.Fil: Alemán, Mercedes. Academia Nacional de Medicina. Instituto de Investigaciones Hematológicas Mariano R. Castex; Argentina.Fil: Sasiain, María C. Academia Nacional de Medicina. Instituto de Investigaciones Hematológicas Mariano R. Castex; Argentina.Fil: de la Barrera, Silvia S. Academia Nacional de Medicina. Instituto de Investigaciones Hematológicas Mariano R. Castex; Argentina.Background. The proinflammatory cytokine interleukin 17 (IL-17) plays an important role in immune responses but it is also associated with tissue-damaging inflammation. So, we evaluated the ability of Mycobacterium tuberculosis clinical isolates to induce IL-17 in tuberculosis (TB) patients and in healthy human tuberculin reactors (PPD1HD). Methods. IL-17, interferon c (IFN-c), and interleukin 23 (IL-23) receptor expression were evaluated ex vivo and cultured peripheral blood mononuclear cells from TB and PPD1HD stimulated with irradiated clinical isolates from multidrug resistant (MDR) outbreaks M (Haarlem family) and Ra (Latin American–Mediterranean family), as well as drug-susceptible isolates belonging to the same families and laboratory strain H37Rv for 48 hours in T-cell subsets by flow cytometry. Results. We observed that: (1) MDR strains M and Ra are stronger IL-17 inducers than drug-susceptible Mtb strains of the Haarlem and Latin American–Mediterranean families, (2) MDR-TB patients show the highest IL-17 expression that is independent on the strain, (3) IL-17 expression is dependent on CD41 and CD81 T cells associates with persistently high antigen load. Conclusions. IL-17–producing T cells could play an immunopathological role in MDR-TB promoting severe tissue damage, which may be associated with the low effectiveness of the second-line drugs employed in the treatment.