InVivoMAb anti-mouse c-Kit (CD117)

Trained immunity is a long-term functional reprogramming of innate cells that allows for the formation of immune memory akin to adaptive responses, but with a more rapid nonspecific response. We recently identified an anti-inflammatory trained immunity response, termed trained tolerogenic immunity (TTI), induced by low virulence Candida dubliniensis, that protects against acute lethal polymicrobial sepsis via myeloid-derived suppressor cells (MDSCs). Trained immunity and MDSCs arise following hematopoietic stem and progenitor cell (HSPC) expansion in the bone marrow. Here, we show that C. dubliniensis induces inoculum-dependent protection and HSPC expansion, whereas depletion of HSPCs following C. dubliniensis immunization abrogates protection. We further show that myeloid progenitors and putative MDSCs are increased in the bone marrow following C. dubliniensis immunization, and that HSPC depletion results in reduced MDSC influx into the peritoneal cavity following lethal challenge. Bone marrow cytokine analysis revealed that mediators associated with MDSC development and trafficking, including G-CSF, CXCL2, and CCL2, are upregulated following C. dubliniensis immunization. Finally, we find that the C-type lectin receptor adaptor protein Card9 is required for C. dubliniensis-induced protection and HSPC expansion, but not fungal trafficking to the bone marrow. Taken together, these results suggest that Card9-dependent fungal recognition in the bone marrow drives myelopoiesis and the induction of immunosuppressive MDSCs that are protective against lethal inflammation and sepsis.IMPORTANCECells of the innate immune system can be "trained" by inducers to have enhanced memory responses, a phenomenon known as trained immunity. We recently identified an anti-inflammatory training response that is induced by low virulence fungal species (i.e., Candida dubliniensis) and is protective against acute lethal polymicrobial sepsis. Trained immunity inducers, including C. dubliniensis, can access the bone marrow and direct hematopoietic responses. Here, we demonstrate that protection is correlated with C. dubliniensis-induced bone marrow expansion, which directs a myeloid bias in the bone marrow and ultimately results in the expansion of protective myeloid-derived suppressor cells. Involvement of the C-type lectin receptor adaptor protein Card9 in the protective response suggests fungal recognition in the bone marrow drives this response. These findings offer new insights into how trained immunity inducers direct differential outcomes, which will inform the development of novel immunotherapeutics to exploit the full spectrum of trained immune responses.

Group 3 innate lymphoid cells (ILC3s) have emerged as an important player in the pathogenesis of neutrophilic asthma. However, the regulatory mechanism supporting ILC3 responses in the lung remains largely unclear. Here, we demonstrated that stem cell factor (SCF) expression is significantly increased and positively correlated with IL-17A and MPO expression in asthmatic patients. Notably, we identified ILC3 as a major IL-17A-producing responder to SCF in the lung. In mice, SCF synergized with IL-1β/IL-23 to enhance pulmonary ILC3 activation and neutrophilic inflammation. Mechanistically, SCF promoted ILC3 proliferation and cytokine production. Transcriptomic analysis revealed that SCF treatment upregulated the genes related to proliferation and Th17 differentiation, associated with increased AKT and STAT3 signaling. In contrast, deficiency of SCF receptor c-Kit reduced ILC3 proliferation and IL-17A production, resulting in the amelioration of airway hyperreactivity (AHR) and neutrophilic inflammation in mouse neutrophilic asthma model. Furthermore, genetic deletion of SCF in fibroblasts revealed fibroblasts as the primary source of SCF for ILC3 activation in the lung. Moreover, administration of imatinib, a c-Kit inhibitor, alleviated LPS, air pollution or ovalbumin/LPS-induced AHR and neutrophilic inflammation. Our findings elucidated a positive modulatory role of SCF/c-Kit signaling in ILC3 responses during neutrophilic inflammation, offering a potential therapeutic target for neutrophilic asthma.

Immunization has long played essential roles in preventing diseases. However, the desire for precision delivery of vaccines to boost a robust immune response remains largely unmet. Here, we describe the use of acupoint delivery of nanovaccines (ADN) to elicit dual-niche immunological priming. ADN can simultaneously stimulate mast cell-assisted maturation of dendritic cells at the acupoint and enable direct delivery of nanovaccines into the draining lymph nodes. We demonstrate that ADN not only provokes antigen presentation by lymph node-resident CD8α+ dendritic cells, but also induces the accumulation of nanovaccines in B-cell zones, amplifying antigen-specific cytotoxic T lymphocyte responses and immunoglobulin G antibody expression in draining lymph nodes. ADN also generates systemic immune responses by causing immune memory and preventing T-cell anergy in the spleen. Further supported by evoking effective antitumor responses and high-level antiviral antibodies in mice, ADN provides a simple yet versatile platform for advanced nanovaccination.

The dynamics of the hematopoietic flux responsible for blood cell production in native conditions remains a matter of debate. Using CITE-seq analyses, we uncovered a distinct progenitor population that displays a cell cycle gene signature similar to the one found in quiescent hematopoietic stem cells. We further determined that the CD62L marker can be used to phenotypically enrich this population in the Flt3+ multipotent progenitor (MPP4) compartment. Functional in vitro and in vivo analyses validated the heterogeneity of the MPP4 compartment and established the quiescent/slow-cycling properties of the CD62L- MPP4 cells. Furthermore, studies under native conditions revealed a novel hierarchical organization of the MPP compartments in which quiescent/slow-cycling MPP4 cells sustain a prolonged hematopoietic activity at steady-state while giving rise to other lineage-biased MPP populations. Altogether, our data characterize a durable and productive quiescent/slow-cycling hematopoietic intermediary within the MPP4 compartment and highlight early paths of progenitor differentiation during unperturbed hematopoiesis.