IFNG and infection: 4-1BB ligation did not induce production of IL-4, a Th2 cytokine, IL-17, a cytokine which contribute to protection to MTB challenge [45], [46] and XCL-1, a chemokine released by suppressor CD8+ T cells during the chronic stage of infection with MTB that negatively affects production of IFN-γ by CD4+ T cells [44].