CD8A and infection: For the development of an effective vaccine against intracellular pathogen represented by Brucella, the production of Th1- derived cytokines (IL-12, TNFα, IFNγ) as well as the activation of macrophages, dendritic cells, and CD4+ and CD8+ T cells are the key factors for the clearance of infection; whereas Th2 immune responses, which are induced by the humoral immune system, have a minor role in the clearance of infection (67).