Coxiella burnetii, the causative agent of Q fever, is an obligate intracellular, primarily pulmonary, bacterial pathogen. Although much is known about adaptive immune responses against this bacterium, our understanding of innate immune responses against C. burnetii is not well defined, particularly within the target tissue for infection, the lung. Previous studies examined the roles of the innate immune system receptors Toll-like receptor 2 (TLR2) and TLR4 in peripheral infection models and described minimal phenotypes in specific gene deletion animals compared to those of their wild-type controls ( Here, we assessed the roles for TLR2, TLR4, and MyD88 in pulmonary C. burnetii infection and compared responses to those that occurred in TLR2-and TLR4-deficient animals following peripheral infection. As observed previously, neither TLR2 nor TLR4 was needed for limiting bacterial growth after peripheral infection. In contrast, TLR2 and, to a lesser extent, TLR4 limited growth (or dissemination) of the bacterium in the lung and spleen after pulmonary infection. TLR2, TLR4, and MyD88 were not required for the general inflammatory response in the lungs after pulmonary infection. However, MyD88 signaling was important for infection-induced morbidity. Finally, TLR2 expression on hematopoietic cells was most important for limiting bacterial growth in the lung. These results expand on our knowledge of the roles for TLR2 and TLR4 in C. burnetii infection and suggest various roles for these receptors that are dictated by the site of infection.

Rich and poor galaxy clusters have the same measured halo metallicity, 0.35-0.4 Z , despite being an order of magnitude apart in stellar fraction, M * /M gas . The measured ICM metallicity in rich clusters cannot be explained by the visible stellar population as stars make up only 5% of the total gas mass. The independence of metallicity from M * /M gas suggests an external and universal source of metals such as an Early Enrichment Population (EEP). Galaxy cluster RX J1416.4+2315 has the lowest stellar fraction known, M * /M gas = 0.015 ± 0.003, and here we improve the halo metallicity determination using archival Chandra and XMM Newton observations. We determine the ICM metallicity of RXJ to be 0.336 ± 0.058 Z within 0.3 < R/R 500 < 0.75, excluding the central galaxy. We combine this measurement with other clusters with a wider range of M * /M gas resulting in the fit of Z tot = (0.37 ± 0.01) + (0.13 ± 0.17)(M * /M gas ). This fit is largely independent of M * /M gas , and shows that for a low M * /M gas system the observed stellar population can make only 10-20% of the total metals. We quantify the Fe contribution of the EEP further by adopting a standard Fe yield for visible stellar population, and find that Z EEP = (0.36 ± 0.01)-(1.44 ± 0.17)(M * /M gas ). To account for the observed Fe mass, a supernova rate of 6.6 ± 3.0 SNe yr −1 (Type Ia) and 5.0 ± 2.5 SNe yr −1 (core collapse) is required over the redshift range 3 < z < 10 for a single galaxy cluster with mass ∼ 3 × 10 14 M at z=0. These supernovae might be visible in JWST observation of high redshift clusters and protoclusters.

Rich and poor galaxy clusters have the same measured halo metallicity, 0.35–0.4 Z ⊙, even though they are an order of magnitude apart in stellar fraction, M */M gas. The measured intracluster medium (ICM) metallicity in high-mass clusters cannot be explained by the visible stellar population as stars typically make up 3%–20% of the total baryon mass. The independence of metallicity of M */M gas suggests an external and universal source of metals such as an early enrichment population (EEP). Galaxy cluster RX J1416.4+2315, classified as a fossil system, has a stellar fraction of M */M gas = 0.054 ± 0.018, and here we improve the halo metallicity determination using archival Chandra and XMM-Newton observations. We determine the ICM metallicity of RXJ1416 to be 0.303 ± 0.053 Z ⊙ within 0.3 < R/R 500 < 1, excluding the central galaxy. We combine this measurement with other clusters with a wider range of M */M gas, resulting in the fit of Z tot = (0.36 ± 0.01) + (0.10 ± 0.17)(M */M gas). This fit is largely independent of M */M gas and shows that for a low M */M gas system, the observed stellar population can make only 10%–20% of the total metals. We quantify the Fe contribution of the EEP further by adopting a standard Fe yield for visible stellar populations, and find that Z EEP = (0.36 ± 0.01) − − (0.96 ± 0.17)(M */M gas). To account for the observed Fe mass, a supernova (SN) rate of 10 ± 5 SNe yr−1 (Type Ia) and 40 ± 19 SNe yr−1 (core collapse) is required over the redshift range 3 < z < 10 for a single galaxy cluster with mass ∼3 × 1014 M ⊙ at z = 0. These SNe might be visible in observations of high-redshift clusters and protoclusters with the James Webb Space Telescope.