CD4 and tuberculosis: Xu et al. [27] evaluated CD27 in CD27−IFN-γ+CD4+ T cells for differential diagnosis in TB-unexposed healthy people, TB contacts, and smear-negative TB and concluded that the percentage of CD27−IFN-γ+CD4+ cells can distinguish smear-negative TB patients from the other two groups (AUC = 0.88, sensitivity 82.1%, specificity 80.0%).