CD4 and respiratory tract infectious disorder: Currently little is known about the immune response needed to protect the lungs from a respiratory infection by Brucella. Recently, Clapp et al. (60) demonstrated that nasal B. melitensis ΔznuA vaccination protects the lung from B. melitensis respiratory infection, and that CD8+ T cells, but not CD4+ and Th17 cells, are essential for this protection.