There appear to be three mechanisms of the adaptive immune response against brucellosis that are important: (1) production of IFN (produced by CD4+, CD8+, and γδ T cells) activates the bactericidal action of the macrophages to hamper the intracellular survival of Brucella; (2) the cytotoxic action of the CD8+ and γδ T cells kills infected macrophages; (3) Th1 antibody IgG2a isotypes opsonize the bacteria to facilitate effective phagocytosis [39, 41]. This evidence concerns the gene CD8A and brucellosis.