IFNG and infection: As described in our previous study, IFN-γ producing cells responded to combined PPD-B (bovine purified protein derivate) and PPD-A (avian purified protein derivate) antigenic stimulation by whole blood IFN-γ release assay (IGRA) enzyme-linked immunosorbent assay (ELISA) and IGRA enzyme-linked immunospot assay (ELISPOT), 2 weeks post-infection, peaking at 7 weeks post-infection and then decreasing.