Psychosocial stress has profound effects on the body, including the immune system and the brain1,2. Although a large number of pre-clinical and clinical studies have linked peripheral immune system alterations to stress-related disorders such as major depressive disorder (MDD)3, the underlying mechanisms are not well understood. Here we show that expression of a circulating myeloid cell-specific proteinase, matrix metalloproteinase 8 (MMP8), is increased in the serum of humans with MDD as well as in stress-susceptible mice following chronic social defeat stress (CSDS). In mice, we show that this increase leads to alterations in extracellular space and neurophysiological changes in the nucleus accumbens (NAc), as well as altered social behaviour. Using a combination of mass cytometry and single-cell RNA sequencing, we performed high-dimensional phenotyping of immune cells in circulation and in the brain and demonstrate that peripheral monocytes are strongly affected by stress. In stress-susceptible mice, both circulating monocytes and monocytes that traffic to the brain showed increased Mmp8 expression following chronic social defeat stress. We further demonstrate that circulating MMP8 directly infiltrates the NAc parenchyma and controls the ultrastructure of the extracellular space. Depleting MMP8 prevented stress-induced social avoidance behaviour and alterations in NAc neurophysiology and extracellular space. Collectively, these data establish a mechanism by which peripheral immune factors can affect central nervous system function and behaviour in the context of stress. Targeting specific peripheral immune cell-derived matrix metalloproteinases could constitute novel therapeutic targets for stress-related neuropsychiatric disorders.
© 2024. The Author(s).

Commensal microbes induce cytokine-producing effector tissue-resident CD4+ T cells, but the function of these T cells in mucosal homeostasis is not well understood. Here, we report that commensal-specific intestinal Th17 cells possess an anti-inflammatory phenotype marked by expression of interleukin (IL)-10 and co-inhibitory receptors. The anti-inflammatory phenotype of gut-resident commensal-specific Th17 cells was driven by the transcription factor c-MAF. IL-10-producing commensal-specific Th17 cells were heterogeneous and derived from a TCF1+ gut-resident progenitor Th17 cell population. Th17 cells acquired IL-10 expression and anti-inflammatory phenotype in the small-intestinal lamina propria. IL-10 production by CD4+ T cells and IL-10 signaling in intestinal macrophages drove IL-10 expression by commensal-specific Th17 cells. Intestinal commensal-specific Th17 cells possessed immunoregulatory functions and curbed effector T cell activity in vitro and in vivo in an IL-10-dependent and c-MAF-dependent manner. Our results suggest that tissue-resident commensal-specific Th17 cells perform regulatory functions in mucosal homeostasis.
Copyright © 2023 Elsevier Inc. All rights reserved.

The mechanisms that guide Th2 cell differentiation in barrier tissues are unclear. Using temporal, spatial and single cell transcriptomic tracking of house dust mite (HDM) specific T cells, we describe the molecular pathways driving allergen specific Th2 cells. Differentiation and migration of lung allergen-specific Th2 cells requires early expression of the transcriptional repressor Blimp-1. Loss of Blimp-1 during priming in the lymph node ablated the formation of Th2 cells that migrate to the lung, indicating early Blimp-1 promotes the population of Th2 cells with migratory capability. Blimp-1 occurs in a subset of lymph node CD4 T cells that requires IL-10 from allergen-specific T cells. Furthermore, IL-2/STAT5 signals are essential for both Blimp-1 and GATA3 upregulation through repression of Bcl6 and Bach2 in the lymph node. Spatial microniches of IL-2 in the lymph node identified by the latent factor discovery method SLIDE discriminate and support the earliest Blimp-1+ migratory Th2 cells, demonstrating that lymph node localization is a primary driver of Th2 initiation. Our findings illuminate the molecular pathways for inhaled allergens to promote Th2 cells and identify an early requirement for IL-2 mediated spatial microniches that synergize with allergen-driven IL-10 from responding T cells to drive allergic asthma

Preculture is indispensable for achieving highly efficient non-homologous end joining (NHEJ)-based genome editing. Here, we present a protocol for optimizing genome editing conditions for murine hematopoietic stem cells (HSCs) and evaluating their function following NHEJ-based genome editing. We describe steps for sgRNA preparation, cell sorting, preculture, and electroporation. We then detail post-editing culture and transplanting of bone marrow. This protocol can be used to study genes related to HSC quiescence. For complete details on the use and execution of this protocol, please refer to Shiroshita et al.1.
Copyright © 2023. Published by Elsevier Inc.

Tissue immunity and responses to injury depend on the coordinated action and communication among physiological systems. Here, we show that, upon injury, adaptive responses to the microbiota directly promote sensory neuron regeneration. At homeostasis, tissue-resident commensal-specific T cells colocalize with sensory nerve fibers within the dermis, express a transcriptional program associated with neuronal interaction and repair, and promote axon growth and local nerve regeneration following injury. Mechanistically, our data reveal that the cytokine interleukin-17A (IL-17A) released by commensal-specific Th17 cells upon injury directly signals to sensory neurons via IL-17 receptor A, the transcription of which is specifically upregulated in injured neurons. Collectively, our work reveals that in the context of tissue damage, preemptive immunity to the microbiota can rapidly bridge biological systems by directly promoting neuronal repair, while also identifying IL-17A as a major determinant of this fundamental process.
Published by Elsevier Inc.