Single-cell transcriptome profiling reveals the immune dysregulation characteristics of mice infected by Brucella abortus.

BACKGROUND Brucellosis poses a significant threat to animal and human health globally. However, how Brucella subverts the immune response to establish persistent infections remains unclear. METHODS We utilized single-cell RNA sequencing (scRNA-seq) to decipher the immune landscape of mice infected by Brucella abortus. Flow cytometry, transgenic cell line and mouse, and antibody blockage were utilized to explore the relevant mechanisms. RESULTS Brucella infection induced significant changes in the composition and signaling pathways of immune cells, and flow cytometry analysis further confirmed the scRNA-seq data. An in-depth analysis with macrophages, the main target cell for Brucella, demonstrated activation of type I IFN and type II IFN signaling, TNF production, diverse cell deaths, etc. Specifically, Vir-2308 Brucella infection induced IFN-β expression, primarily originating from macrophages. In vitro, a significantly lower level of intracellular Brucella survival was observed in ifnar1-/- macrophages. In vivo, ifnar1 genetic deficiency rendered the mice less susceptible to Brucella challenge with a lower bacterial load and higher levels of macrophages and neutrophils. Interestingly, Brucella infection induced a dramatic reduction of NK cells along with the upregulation of CD94:NKG2A, one typical immune checkpoint module of NK cells. Further blockage of the NKG2A receptor in mice significantly reduced the bacterial load in the tissues, concurrent with a higher ratio of mature dendritic cells and a lower proportion of B cells. CONCLUSIONS scRNA-seq revealed that Brucella infection significantly alters the immune microenvironment in mice, providing insight into a better understanding of brucellosis pathogenesis and the immune evasion strategies of this sophisticated pathogen.