For many years, the high-affinity receptor for immunoglobulin E (IgE) FcεRI, which is expressed by mast cells and basophils, has been widely held to be the exemplar of cross-linking (that is, aggregation dependent) signaling receptors. We found, however, that FcεRI signaling could occur in the presence or absence of receptor cross-linking. Using both cell and cell-free systems, we showed that FcεRI signaling was stimulated by surface-associated monovalent ligands through the passive, size-dependent exclusion of the receptor-type tyrosine phosphatase CD45 from plasma membrane regions of FcεRI-ligand engagement. Similarly to the T cell receptor, FcεRI signaling could also be initiated in a ligand-independent manner. These data suggest that a simple mechanism of CD45 exclusion–based receptor triggering could function together with cross-linking–based FcεRI signaling, broadening mast cell and basophil reactivity by enabling these cells to respond to both multivalent and surface-presented monovalent antigens. These findings also strengthen the case that a size-dependent, phosphatase exclusion–based receptor triggering mechanism might serve generally to facilitate signaling by noncatalytic immune receptors.

Mucosal surfaces such as fish gills interface between the organism and the external environment and as such are major sites of foreign Ag encounter. In the gills, the balance between inflammatory responses to waterborne pathogens and regulatory responses toward commensal microbes is critical for effective barrier function and overall fish health. In mammals, IL-4 and IL-13 in concert with IL-10 are essential for balancing immune responses to pathogens and suppressing inflammation. Although considerable progress has been made in the field of fish immunology in recent years, whether the fish counterparts of these key mammalian cytokines perform similar roles is still an open question. In this study, we have generated IL-4/13A and IL-4/13B mutant zebrafish (Danio rerio) and, together with an existing IL-10 mutant line, characterized the consequences of loss of function of these cytokines. We demonstrate that IL-4/13A and IL-4/13B are required for the maintenance of a Th2-like phenotype in the gills and the suppression of type 1 immune responses. As in mammals, IL-10 appears to have a more striking anti-inflammatory function than IL-4–like cytokines and is essential for gill homeostasis. Thus, both IL-4/13 and IL-10 paralogs in zebrafish exhibit aspects of conserved function with their mammalian counterparts.

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Acetylcholine (ACh) from neuronal and non-neuronal sources plays an important role in the regulation of immune responses and is associated with the development of several disease pathologies. We have previously demonstrated that group 2 innate lymphoid cell (ILC2)-derived ACh is required for optimal type 2 responses to parasitic infection and therefore sought to determine whether this also plays a role in allergic inflammation. RoraCre+ChatLoxP mice (in which ILC2s cannot synthesize ACh) were exposed to an allergenic extract of the fungus Alternaria alternata, and immune responses in the airways and lung tissues were analyzed. Airway neutrophilia and expression of the neutrophil chemoattractants CXCL1 and CXCL2 were enhanced 24 h after exposure, suggesting that ILC2-derived ACh plays a role in limiting excessive pulmonary neutrophilic inflammation. The effect of non-selective depletion of ACh was examined by intranasal administration of a stable parasite-secreted acetylcholinesterase. Depletion of airway ACh in this manner resulted in a more profound enhancement of neutrophilia and chemokine expression, suggesting multiple cellular sources for the release of ACh. In contrast, depletion of ACh inhibited Alternaria-induced activation of ILC2s, suppressing the expression of IL-5, IL-13, and subsequent eosinophilia. Depletion of ACh reduced macrophages with an alternatively activated M2 phenotype and an increase in M1 macrophage marker expression. These data suggest that ACh regulates allergic airway inflammation in several ways, enhancing ILC2-driven eosinophilia but suppressing neutrophilia through reduced chemokine expression.

The study of respiratory tissue damage and repair is critical to understand not only the consequences of respiratory tissue exposure to infectious agents, irritants and toxic chemicals, but also to comprehend the pathogenesis of chronic inflammatory lung diseases. To gain further insights into these processes, we developed a gill cryoinjury model in the adult zebrafish. Time course analysis showed that cryoinjury of the gills triggered an inflammatory response, extensive cell death and collagen deposition at the site of injury. However, the inflammation was rapidly resolved, collagen accumulation dissipated and by 3 weeks after injury the affected gill tissue had begun to regenerate. RNA seq analysis of cryoinjured gills, combined with a comparison of zebrafish heart cryoinjury and caudal fin resection datasets, highlighted the differences and similarities of the transcriptional programmes deployed in response to injury in these three zebrafish models. Comparative RNA seq analysis of cryoinjured zebrafish gills with mouse pulmonary fibrosis datasets also identified target genes, including the understudied FIBIN, as differentially expressed in the two species. Further mining, including of human datasets, suggests that FIBIN may contribute to the successful resolution of tissue damage without fibrosis.

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26Healthy fish stocks are central to global food security. Key to fish health is robust 27 immunity at mucosal surfaces, and especially at the gills. However, a balance must be 28 struck between tolerating commensal microorganisms and reacting appropriately 29 toward pathogens. In mammals, IL-4 and IL-13 in concert with IL-10 are essential 30 for balancing immune response to pathogens and suppressing inflammation. Whether 31 their fish counterparts perform similar roles is an open question. Here, we have 32 generated IL-4/13A and IL-4/13B mutant zebrafish and, together with existing IL-10 33 mutants, characterized the consequences of loss-of-function of these cytokines. We 34 demonstrate that these cytokines are required to suppress inflammation. Further, IL-35 4/13A and IL-4/13B are required for the maintenance of a Th2-like phenotype in the 36 gills. As in mammals, IL-10 appears to have a more striking anti-inflammatory 37 function than IL-4-like cytokines. Thus, both IL-10 and IL-4/13 paralogues in 38 zebrafish exhibit aspects of conserved function with their mammalian counterparts. 39 40 42cytokines that participate in several physiological processes but are mainly known for 43 stimulating type 2 immune responses (1), characterised by mucus overproduction, IgE 44 antibody production, eosinophilia and differentiation of alternatively activated (M2) 45 macrophages (2). These responses confer protection against parasites but, when 46 inappropriately activated, contribute to the development of asthma and allergic 47 inflammation (1). IL-4 and IL-13 are secreted by CD4 + Th2 cells, basophils, 48 eosinophils, mast cells and group 2 innate lymphoid cells (ILC2s) (3). They exert 49 their functions by binding to two types of receptor complexes: a type I receptor, 50 3 constituted by the IL-4Rα chain and the IL-2R common γ chain (γc) and a type II 51 receptor, which comprises IL-4Rα chain and IL-13Rα1 subunits. Both type I and type 52 II receptors signal through STAT6 transcription factor binding to promoter elements 53 within IL-4/IL-13 responsive genes (4). IL-4 and IL-13 suppress inflammatory 54 responses by antagonising production of TNFα, IL-1β and other pro-inflammatory 55 mediators (5) and act in opposition to IFN-γ, the canonical Th1 (type 1) cytokine (6). 56Indeed, co-ordinately with inducing type 2 immune response, IL-4 and IL-13 suppress 57 type 1 responses, characterised by immune cell mediated destruction of cells infected 58 with intracellular pathogens (7). 59Although IL-4 and IL-13 can negatively regulate inflammatory responses, IL-60 10 has the more central anti-inflammatory role in mammals, potently suppressing 61 IFN-γ responses. IL-10 can suppress a range of aberrant immune responses including 62 both type 1 and type 2 responses (8). IL-10 is produced by many cell types (9). It 63 regulates CD4 + Treg cell differentiation and function, and it is important in 64 maintaining homeostasis at mucosal surfaces (10). 65Evidence is emerging that fish immune responses can also be classified as 66 type 1 or t...

Our organization, Black in Immuno (@BlackInImmuno), was formed in September 2020 to celebrate, support, and amplify Black voices in immunology when social media campaigns like #BlackInTheIvory illuminated the shared overt and covert issues of systemic racism faced by Black researchers in all facets of science, technology, engineering, art, and mathematics. Black in Immuno was cofounded by a group of Black immunology trainees working at multiple institutions globally: Jo€ el Babdor, E.