During primary infection, the rare naïve CD4+ T cells, which by chance express TCRs complementary to bacterial pMHCII complexes, proliferate and differentiate into Th1, Th2, or Th17 effector cells that produce cytokines such as IFN-γ, IL-4 or IL-17, respectively, which help to eliminate the pathogen. Here, IFNG is linked to infection.