CD4 and tuberculosis: Indeed, these T-cell subsets have been shown to participate in human host defense against Mtb infection in patients with active TB (Behr-Perst et al., 1999; Gansert et al., 2003; Jiang et al., 2014) and a decrease of CD69 expression on TCR Vα7.2+ CD4– T cells was reported to be associated with impaired cytotoxic functions in chronic hepatitis B virus-infected patients (Yong et al., 2017).