Coxiella burnetii strains elicit distinct inflammatory responses in human macrophages.

Coxiella burnetii, the causative agent of human Q fever, subverts macrophage antimicrobial functions to establish an intracellular replicative niche. To better understand the host-pathogen interactions, we investigated the transcriptional responses of human alveolar macrophages (hAMs) infected with virulent (NMI, G), attenuated (NMII), and avirulent (Dugway) strains of C. burnetii. RNA sequencing analysis revealed that all strains activated proinflammatory pathways, particularly IL-17 signaling, though the magnitude and nature of the response varied by strain. Dugway infection induced the most robust transcriptional response and consistent M1-like macrophage polarization, while responses to NMI and NMII were more variable. Cytokine assays confirmed significant secretion of effectors downstream of IL-17 signaling, but only at later stages of infection. Single-cell RNA sequencing further revealed heterogeneity in macrophage response to C. burnetii infection, with distinct subpopulations exhibiting divergent inflammatory profiles. These findings highlight the complexity of macrophage responses to C. burnetii and underscore the importance of strain-specific and cell-specific factors in shaping host immunity. Understanding these dynamics may inform the development of targeted therapies for Q fever.