Combating pulmonary Coxiella burnetii infection: The role of innate immunity. (37.54)

Abstract

Abstract The innate immune system provides first line host defense. However, within the immune privileged site of the lung, immune response must be closely regulated. As a result, tissue resident alveolar macrophages (AM) are typically immunosuppressed. The intracellular bacteria Coxiella burnetii has been observed within AM during infection and little is known about the role of AM in C. burnetii infection. Therefore, the AM deserves focused study. We hypothesized that, due to the immunosuppressed state of resident AM, these macrophages are particularly susceptible to C. burnetii infection and provide a required niche for infection. Dye labeling techniques were employed to discriminate AM and C. burnetii, allowing for the determination of resident and infected cell populations. These techniques were corroborated with antibody labeling and the various populations were analyzed. We report here that resident AM are infected, even at low infective doses. Interestingly, a heterogeneous population of infected cells is also identifiable. This population is comprised of resident CD11c+ AM expressing CD11b and recruited CD11b+ cells expressing CD11c. These findings suggest CD11c expression serves as a marker of cells susceptible to C. burnetii infection. Identification of this susceptible population may aid vaccine development and prove relevant for treatment of other intracellular bacteria, such as, Mycobacterium tuberculosis and Legionella pneumophila.