SummaryGroup 3 innate lymphoid cells (ILC3s) sense environmental signals and are critical for tissue integrity in the intestine. Yet, which signals are sensed and what receptors control ILC3 function remain poorly understood. Here, we show that ILC3s with a lymphoid-tissue-inducer (LTi) phenotype expressed G-protein-coupled receptor 183 (GPR183) and migrated to its oxysterol ligand 7α,25-hydroxycholesterol (7α,25-OHC). In mice lacking Gpr183 or 7α,25-OHC, ILC3s failed to localize to cryptopatches (CPs) and isolated lymphoid follicles (ILFs). Gpr183 deficiency in ILC3s caused a defect in CP and ILF formation in the colon, but not in the small intestine. Localized oxysterol production by fibroblastic stromal cells provided an essential signal for colonic lymphoid tissue development, and inflammation-induced increased oxysterol production caused colitis through GPR183-mediated cell recruitment. Our findings show that GPR183 promotes lymphoid organ development and indicate that oxysterol-GPR183-dependent positioning within tissues controls ILC3 activity and intestinal homeostasis.

Dendritic cells (DCs) and monocytes are crucial mediators of innate and adaptive immune responses during viral infection, but misdirected responses by these cells may contribute to immunopathology. Here, we performed high-dimensional flow cytometry-analysis focusing on mononuclear phagocyte (MNP) lineages in SARS-CoV-2–infected patients with moderate and severe COVID-19. We provide a deep and comprehensive map of the MNP landscape in COVID-19. A redistribution of monocyte subsets toward intermediate monocytes and a general decrease in circulating DCs was observed in response to infection. Severe disease coincided with the appearance of monocytic myeloid-derived suppressor cell-like cells and a higher frequency of pre-DC2. Furthermore, phenotypic alterations in MNPs, and their late precursors, were cell-lineage–specific and associated either with the general response against SARS-CoV-2 or COVID-19 severity. This included an interferon-imprint in DC1s observed in all patients and a decreased expression of the coinhibitory molecule CD200R in pre-DCs, DC2s, and DC3 subsets of severely sick patients. Finally, unsupervised analysis revealed that the MNP profile, alone, pointed to a cluster of COVID-19 nonsurvivors. This study provides a reference for the MNP response to SARS-CoV-2 infection and unravels mononuclear phagocyte dysregulations associated with severe COVID-19.

Here, we characterize the major NK cell populations in the human lung. Our data suggest a model in which the majority of NK cells in the human lung dynamically move between blood and the lung rather than residing in the lung as bona fide tissue-resident CD69 NK cells.

Immune cell differentiation is critical for adequate tissue-specific immune responses to occur. Here, we studied differentiation of human uterine natural killer cells (uNK cells). These cells reside in a tissue undergoing constant regeneration and represent the major leukocyte population at the maternal-fetal interface. However, their physiological response during the menstrual cycle and in pregnancy remains elusive. By surface proteome and transcriptome analysis as well as using humanized mice, we identify a differentiation pathway of uNK cells in vitro and in vivo with sequential acquisition of killer cell immunoglobulin-like receptors and CD39. uNK cell differentiation occurred continuously in response to the endometrial regeneration and was driven by interleukin-15. Differentiated uNK cells displayed reduced proliferative capacity and immunomodulatory function including enhanced angiogenic capacity. By studying human uterus transplantation and monozygotic twins, we found that the uNK cell niche could be replenished from circulation and that it was under genetic control. Together, our study uncovers a continuous differentiation pathway of human NK cells in the uterus that is coupled to profound functional changes in response to local tissue regeneration and pregnancy.

Since the outset of the COVID-19 pandemic, increasing evidence suggests that the innate immune responses play an important role in the disease development. A dysregulated inflammatory state has been proposed as a key driver of clinical complications in COVID-19, with a potential detrimental role of granulocytes. However, a comprehensive phenotypic description of circulating granulocytes in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)−infected patients is lacking. In this study, we used high-dimensional flow cytometry for granulocyte immunophenotyping in peripheral blood collected from COVID-19 patients during acute and convalescent phases. Severe COVID-19 was associated with increased levels of both mature and immature neutrophils, and decreased counts of eosinophils and basophils. Distinct immunotypes were evident in COVID-19 patients, with altered expression of several receptors involved in activation, adhesion, and migration of granulocytes (e.g., CD62L, CD11a/b, CD69, CD63, CXCR4). Paired sampling revealed recovery and phenotypic restoration of the granulocytic signature in the convalescent phase. The identified granulocyte immunotypes correlated with distinct sets of soluble inflammatory markers, supporting pathophysiologic relevance. Furthermore, clinical features, including multiorgan dysfunction and respiratory function, could be predicted using combined laboratory measurements and immunophenotyping. This study provides a comprehensive granulocyte characterization in COVID-19 and reveals specific immunotypes with potential predictive value for key clinical features associated with COVID-19.

Dendritic cells (DCs) are professional antigen-presenting cells, orchestrating innate and adaptive immunity during infections, autoimmune diseases, and malignancies. Since the discovery of DCs almost 50 years ago, our understanding of their biology in humans has increased substantially. Here, we review both antitumor and tolerogenic DC responses in cancer and discuss lineage-specific contributions by their functionally specialized subsets, including the conventional DC (cDC) subsets cDC1 and cDC2, the newly described DC3, and the plasmacytoid DCs (pDCs), focusing on the human setting. In addition, we review the lineage-unrestricted “mature DCs enriched in immunoregulatory molecules” (mregDC) state recently described across different human tumors.

This study provides the first evidence of CXCR1(+)CXCR2(+)IL-23-producing neutrophils that infiltrate and accumulate in inflamed colon tissue of patients with IBD. Thus, this novel source of IL-23 may play a key role in disease progression and will be important to take into consideration in the development of future strategies to monitor, treat and prevent IBD.

Monocytes and dendritic cells are crucial mediators of innate and adaptive immune responses during viral infection, but misdirected responses by these cells might contribute to immunopathology. A comprehensive map of the mononuclear phagocyte (MNP) landscape during SARS-CoV-2 infection and concomitant COVID-19 disease is lacking. We performed 25-color flow cytometry-analysis focusing on MNP lineages in SARS-CoV-2 infected patients with moderate and severe COVID-19. While redistribution of monocytes towards intermediate subset and decrease in circulating DCs occurred in response to infection, severe disease associated with appearance of Mo-MDSC-like cells and a higher frequency of pre-DC2. Furthermore, phenotypic alterations in MNPs, and their late precursors, were cell-lineage specific and in select cases associated with severe disease. Finally, unsupervised analysis revealed that the MNP profile, alone, could identify a cluster of COVID-19 non-survivors. This study provides a reference for the MNP response to clinical SARS-CoV-2 infection and unravel myeloid dysregulation associated with severe COVID-19.