A. baumannii is another critically important pathogen as recognized by the CDC for its multi-drug resistant capacity and ability to cause opportunistic infections. It is a Gram negative pathogen that is on the increase in intensive care units. We have begun to develop in vivo models to better examine the contribution type I and III IFNs play in the host response to this organism as well as dissecting bacterial factors important in its defense against the host response. As part of this work in respiratory infections we identified a sex difference in the susceptibility of mice to infection as well as the respective role for alveolar macrophages in infection.