CD4 and infection: To measure SCV2 specific CD4+ T cells we utilized an ORF3A266-280 MHC-II I-Ab tetramer and 4 weeks after sub-lethal infection detected approximately 1-2% of effector CD4 T cells that stained positive for the reagent (blue symbols) by flow cytometry, compared to less than 1% in Mtb co-infected mice (purple symbols) and 0.5% non-specific staining background in SCV2 unexposed animals (red symbols) (Figure 4A).