It is well recognized that the two key components of the protective reaction in infected animals are the formation of Th1 CD4+ lymphocytes secreting interferon-gamma (IFN-γ), a critical cytokine which is required to regulate the anti-brucellosis activity of macrophages [4], and CD8+ T lymphocytes that lyse Brucella-infected cells [5]. This evidence concerns the gene CD4 and brucellosis.