Alternatively, the Bvg - phase survives in the environment. In normal mice, mutants in Cya have a negligible phenotype in that both wt and the mutant are cleared from the lung. The target of Cya is thought to be neutrophils. Recall, B. bronchiseptica establishes respiratory tract infections in laboratory animals and persists for th life of the animal and is asymptomatic in immuncompetend hosts. Data suggests that Type III secretion suppresses acquired immunity.
Data are consistent with the action of macrophages releasing cytokines that cause death.
In vitro, wildtype B. bronchiseptica induced apoptosis in macrophages, but the Type III mutants did not.