CD4 and infection: However, the frequencies of Mtb-specific cytokine positive cells in IGRA-ve controls was low in keeping with ours [50] and previous studies [45, 51], showing higher frequencies of Mtb-specific CD4+ T cells in PTB, due to stimulation by ongoing infection and therefore, no significant difference was observed between HLA-DR- and HLA-DR+Mtb-specific Teff cells in IGRA-ve samples with the exception of the most abundant IFNγ+Mtb-specific Teff cells (Fig 7B).