We and others have found that some live attenuated Salmonella vaccines, such as aromatic-dependent (aro) mutants, htrA mutants, and aroA htrA double mutants, can cause lethal infections in immunodeficient mice such as those lacking in the production of reactive oxygen species (ROS), interleukin-12 (IL-12), or gamma interferon (IFN-γ) and in mice lacking T cells (9, 10). Here, HTRA1 is linked to infection.