IL17A and infection: In addition to the function of TH17 cells as a substitute for a defective TH1 response, synergism between TH17 and TH1 cells is proposed following infection or postvaccination challenge with Mycobacterium sp., based on the observation that IL-17−/− mice revealed a reduced IFN-γ production by CD4+ T cells and impaired granuloma formation and expression of chemokines CXCL9, CXCL10, and CXCL11 [61].