Neutrophil-mediated innate immune resistance to bacterial pneumonia is dependent on Tet2 function.

Individuals with clonal hematopoiesis of indeterminate potential (CHIP) are at increased risk of aging related health conditions and all-cause mortality, but whether CHIP affects risk of infection is much less clear. Using UK Biobank data, we revealed a positive association between CHIP and incident pneumonia in 438,421 individuals. We show that inflammation enhanced pneumonia risk, as CHIP carriers with a hypomorphic IL6 receptor polymorphism were protected. To better characterize the pathways of susceptibility, we challenged hematopoietic Tet Methylcytosine Dioxygenase 2-knockout (Tet2-/-) and floxed control mice (Tet2fl/fl) with Streptococcus pneumoniae. As with human CHIP carriers, Tet2-/- mice had hematopoietic abnormalities resulting in the expansion of inflammatory monocytes and neutrophils in peripheral blood. Yet, these cells were insufficient in defending against S. pneumoniae and resulted in increased pathology, impaired bacterial clearance, and higher mortality in Tet2-/- mice. We delineated the transcriptional landscape of Tet2-/- neutrophils and found that, while inflammation-related pathways were upregulated in Tet2-/- neutrophils, migration and motility pathways were compromised. Using live-imaging techniques, we demonstrated impairments in motility, pathogen uptake, and neutrophil extracellular trap (NET) formation by Tet2-/- neutrophils. Collectively, we show that CHIP is a risk factor for bacterial pneumonia related to innate immune impairments.

Coating M-CSF on plastic surface results in the generation of increased numbers of macrophages in vitro.

Macrophages are one of the important cell types in the innate immune system that are present in various anatomical regions of the body and promote early control of pathogens. The relative proportion of macrophages in various lymphoid and non-lymphoid regions is small, and as such it is tedious to purify these cells to homogeneity. Culture of bone marrow precursors with macrophage colony-stimulating factor (M-CSF) results in their differentiation to macrophages, however this procedure results in low numbers of differentiated macrophages. Herein we reveal a new approach of generating increased numbers of differentiated macrophages from bone marrow precursors. We show that M-CSF delivered in a plate-bound form results in the differentiation of significantly more macrophages in comparison to soluble M-CSF. Furthermore, the macrophages differentiated with plate-bound M-CSF display increased metabolic activity and cell death following infection with pathogens.