Distinct regulatory machineries underlying divergent chromatin landscapes distinguish innate lymphoid cells from T helper cells.

Innate lymphoid cells (ILCs), as the innate counterpart of CD4+ T helper (Th) cells, play crucial roles in maintaining tissue homeostasis. While the ILC subsets and their corresponding Th subsets demonstrate significant similarities in core programming related to effector function and regulatory mechanisms, their principal distinctions, given their innate and adaptive lymphocyte nature, remain largely unknown. In this study, we have employed an integrative analysis of 294 bulk RNA-sequencing results across all ILC and Th subsets, using scRNA-seq algorithms. Consequently, we identify two genesets that predominantly differentiate ILCs from Th cells, as well as three genesets that distinguish various immune responses. Furthermore, through chromatin accessibility analysis, we find that the ILC geneset tends to rely on specific transcriptional regulation at promoter regions compared with the Th geneset. Additionally, we observe that ILCs and Th cells are under differential transcriptional regulation. For example, ILCs are under stronger regulation by multiple transcription factors, including RORα, GATA3, and NF-κB. Otherwise, Th cells are under stronger regulation by AP-1. Thus, our findings suggest that, despite the acknowledged similarities in effector functions between ILC subsets and corresponding Th subsets, the underlying regulatory machineries still exhibit substantial distinctions. These insights provide a comprehensive understanding of the unique roles played by each cell type during immune responses.

IL-21R-STAT3 signalling initiates a differentiation program in uterine tissue-resident NK cells to support pregnancy.

Tissue-resident Natural Killer (trNK) cells are crucial components of local immunity that activate rapidly upon infection. However, under steady state conditions, their responses are tightly controlled to prevent unwanted tissue damage. The mechanisms governing their differentiation and activation are not fully understood. Here, we characterise uterine trNK cells longitudinally during pregnancy by single cell RNA sequencing and find that the combined expression pattern of 4-1BB and CD55 defines their three distinct stages of differentiation in mice. Mechanistically, an IL-21R-STAT3 axis is essential for initiating the trNK cell differentiation. The fully differentiated trNK cells demonstrate enhanced functionality, which is necessary for remodelling spiral arteries in the decidua. We identify an apoptotic program that is specific to the terminal differentiation stage, which may preclude tissue damage by these highly activated trNK cells. In summary, uterine trNK cells become intensely active and effective during pregnancy, but tightly controlled via a differentiation program that also limits potential harm, suggesting an intricate mechanism for harnessing trNK cells in maintaining pregnancy.

Proline uptake promotes activation of lymphoid tissue inducer cells to maintain gut homeostasis.

Metabolic regulation is integral to the proper functioning of innate lymphoid cells, yet the underlying mechanisms remain elusive. Here, we show that disruption of exogenous proline uptake, either through dietary restriction or by deficiency of the proline transporter Slc6a7, in lymphoid tissue inducer (LTi) cells, impairs LTi activation and aggravates dextran sodium sulfate-induced colitis in mice. With an integrative transcriptomic and metabolomic analysis, we profile the metabolic characteristics of various innate lymphoid cell subsets and reveal a notable enrichment of proline metabolism in LTi cells. Mechanistically, defective proline uptake diminishes the generation of reactive oxygen species, previously known to facilitate LTi activation. Additionally, LTi cells deficient in Slc6a7 display downregulation of Cebpb and Kdm6b, resulting in compromised transcriptional and epigenetic regulation of interleukin-22. Furthermore, our study uncovers the therapeutic potential of proline supplementation in alleviating colitis. Therefore, these findings shed light on the role of proline in facilitating LTi activation and ultimately contributing to gut homeostasis.

PD-1 signaling facilitates activation of lymphoid tissue inducer cells by restraining fatty acid oxidation.

Anti-programmed death-1 (PD-1) immunotherapy that aims to restore T cell activity in cancer patients frequently leads to immune-related adverse events such as colitis. However, the underlying mechanism is still elusive. Here, we find that Pdcd1-deficient mice exhibit disrupted gut microbiota and aggravated dextran sulfate sodium (DSS)-induced colitis. In addition to T cells, PD-1 is also substantially expressed in colonic lymphoid tissue inducer (LTi) cells. During DSS-induced colitis, LTi cell activation is accompanied by increased PD-1 expression, whereas PD-1 deficiency results in reduced interleukin-22 (IL-22) production by LTi cells and exacerbated inflammation. Mechanistically, activated LTi cells reprogram their metabolism toward carbohydrate metabolism and fatty acid synthesis, while fatty acid oxidation (FAO) is unchanged. However, PD-1 deficiency leads to significantly elevated FAO in LTi cells, which in turn attenuates their activation and IL-22 production. Consistently, FAO suppression efficiently restores IL-22 production in Pdcd1-/- LTi cells. Thus, our study provides unforeseen mechanistic insight into colitis occurrence during anti-PD-1 immunotherapy through LTi cell metabolic reconfiguration.

Abnormal Epigenetic Regulations in the Immunocytes of Sjögren's Syndrome Patients and Therapeutic Potentials.

Sjögren's syndrome (SjS), characterized by keratoconjunctivitis sicca and dry mouth, is a common autoimmune disease, especially in middle-aged women. The immunopathogenesis of SjS is caused by the sequential infiltration of T and B cells into exocrine glands, including salivary and lacrimal glands. Effector cytokines produced by these immunocytes, such as interferons (IFNs), IL-17, IL-22, IL-21, IL-4, TNF-α, BAFF and APRIL, play critical roles in promoting autoimmune responses and inducing tissue damages. Epigenetic regulations, including DNA methylation, histone modification and non-coding RNAs, have recently been comprehensively studied during the activation of various immunocytes. The deficiency of key epigenetic enzymes usually leads to aberrant immune activation. Epigenetic modifications in T and B cells are usually found to be altered during the immunopathogenesis of SjS, and they are closely correlated with autoimmune responses. In particular, the important role of methylation in activating IFN pathways during SjS progression has been revealed. Thus, according to the involvement of epigenetic regulations in SjS, target therapies to reverse the altered epigenetic modifications in auto-responsive T and B cells are worthy of being considered as a potential therapeutic strategy for SjS.