Temporally Resolved Single-Cell RNA Sequencing Reveals Pathogenesis and Immune Responses in Intracerebral Bacille Calmette-Guérin (BCG) Infection.

Background

In some children with immunodeficiency, Bacille Calmette-Guérin (BCG) vaccination can lead to dissemination and severe infection, including severe intracranial infection, called disseminated BCG disease (BCGosis), which is characterized by high rates of disability and mortality. However, the specific routes by which BCG crosses CNS barriers and the patterns of temporal remodeling of the CNS immune microenvironment during infection have yet to be fully elucidated.

Methods

Mice were infected with BCG through tail vein injection to construct an intracerebral mycobacterial infection mouse model, wherein the brain was collected and analyzed using single-cell RNA sequencing. We profiled temporal transcriptomic changes in cell populations, pathways, and cell-cell communication associated with anti-mycobacterial activity and inflammation-induced disturbance of physiological brain activities.

Results

After BCG was injected via tail vein, histopathological images and cultured colonies of brain tissue confirmed successful brain infection. Then, whole-brain tissue was dissected for 10× Genomics single-cell sequencing, and we acquired 15 cell types. Dysfunction and inflammatory responses were observed in endothelial and ependymal cells. Infection induced dynamic state transitions in microglia, enabling their differentiation into disease-related and interferon-responsive states. Along with peripheral immune cells, microglia formed temporally structured communication networks that mediated early events such as chemokine recruitment and inflammatory storms, and facilitated late-stage immune checkpoint upregulation.

Conclusions

This study proposes BCSFB as a possible pathway of mycobacteria invasion and reveals the temporality of immune response processes in the pathogenesis of intracerebral mycobacterial infection.