CD27 and tuberculosis: Based on previous studies [9–14], MTB-specific CD4+ T cell activation markers of CD27, CD38, IFN-γ, HLA-DR and Ki-67 are able to distinguish active TB and LTBI, especially the expression of CD27−CD38+ in IFN-γ+CD4+ T cells can be used as an effective marker for the differential diagnosis of active PTB, latent tuberculosis infection (LTBI) and healthy controls.