Megakaryocytes (MKs) continuously produce platelets in bone marrow to support hemostasis. However, MKs also play roles beyond thrombopoiesis as they regulate hematopoietic stem cell quiescence and erythropoiesis, which suggests the functional heterogeneity of MKs. Here, using single-cell sequencing we identified an MK-derived immune-stimulating cell (MDIC) population, which plays an important role in host-protective response against bacteria. In contrast to platelet-generating MKs, MDICs highly express cell migration, immune-modulatory, and response genes. Upon Listeria (L.) monocytogenes infection, MDICs egress to circulation and infiltrate into the spleen, liver and lung. MDICs interact with myeloid cells to promote their migration and tissue infiltration. More importantly, MDICs stimulate phagocytosis of macrophages and neutrophils by producing TNFα and IL-6 and facilitating antigen-specific T cell activation via IL-6 to enhance anti-bacterial response. Ablation of MKs reduced innate immune response and compromised T cell activation in spleen and liver, impairs the anti-bacterial effects in mice under L. monocytogenes challenge. Finally, infection-induced emergency megakaryopoiesis efficiently stimulated MDICs generation upon bacterial infection. Overall, we identify MDICs as a novel MK subpopulation, which regulates host-defense immune response against bacterial infection.
Effectors Targeting the Unfolded Protein Response during Intracellular Bacterial Infection
