CD4 and brucellosis: CD4+ and CD8+ T lymphocytes are the primary producers of IFN-γ in brucellosis and both appear to play key roles in the protective immune response, although the relative importance of each subset compared to the other remains controversial and appears to be influenced by route of infection and strain administered (Mambres et al., 2016; Pascual et al., 2019; Wang et al., 2020).