Using B. abortus and B. melitensis, it was found that dendritic cells, macrophages and CD8+ T cells (Oliveira and Splitter, 1995; Copin et al., 2007; Macedo et al., 2008; Salcedo et al., 2008) are the key components of the host cellular immunity to control infection in mouse models. This evidence concerns the gene CD8A and infection.