CD4+ T cells are at the nexus of the innate and adaptive arms of the immune system. However, little is known about the evolutionary history of CD4+ T cells, and it is unclear whether their differentiation into specialized subsets is conserved in early vertebrates. In this study, we have created transgenic zebrafish with vibrantly labeled CD4+ cells allowing us to scrutinize the development and specialization of teleost CD4+ leukocytes in vivo. We provide further evidence that CD4+ macrophages have an ancient origin and had already emerged in bony fish. We demonstrate the utility of this zebrafish resource for interrogating the complex behavior of immune cells at cellular resolution by the imaging of intimate contacts between teleost CD4+ T cells and mononuclear phagocytes. Most importantly, we reveal the conserved subspecialization of teleost CD4+ T cells in vivo. We demonstrate that the ancient and specialized tissues of the gills contain a resident population of il-4/13b–expressing Th2-like cells, which do not coexpress il-4/13a. Additionally, we identify a contrasting population of regulatory T cell–like cells resident in the zebrafish gut mucosa, in marked similarity to that found in the intestine of mammals. Finally, we show that, as in mammals, zebrafish CD4+ T cells will infiltrate melanoma tumors and obtain a phenotype consistent with a type 2 immune microenvironment. We anticipate that this unique resource will prove invaluable for future investigation of T cell function in biomedical research, the development of vaccination and health management in aquaculture, and for further research into the evolution of adaptive immunity.

Mutations affecting Gαq proteins are pervasive in uveal melanoma (UM), suggesting they ‘drive’ UM pathogenesis. The ERK1/2-MAPK pathway is critical for cutaneous melanoma development and consequently an important therapeutic target. Defining the contribution of ERK1/2-MAPK signalling to UM development has been hampered by the lack of an informative animal model that spontaneously develops UM. Towards this end, we engineered transgenic zebrafish to express oncogenic GNAQQ209P in the melanocyte lineage. This resulted in hyperplasia of uveal melanocytes, but with no evidence of malignant progression, nor perturbation of skin melanocytes. Combining expression of oncogenic GNAQQ209P with p53 inactivation resulted in earlier onset and even more extensive hyperplasia of uveal melanocytes that progressed to UM. Immunohistochemistry revealed only weak immunoreactivity to phosphorylated (p)ERK1/2 in established uveal tumours—in contrast to strong immunoreactivity in oncogenic RAS-driven skin lesions—but ubiquitous positive staining for nuclear Yes-associated protein (YAP). Moreover, no changes were observed in pERK1/2 levels upon transient knockdown of GNAQ or phospholipase C-beta (PLC-β) inhibition in the majority of human UM cell lines we tested harbouring GNAQ mutations. In summary, our findings demonstrate a weak correlation between oncogenic GNAQQ209P mutation and sustained ERK1/2-MAPK activation, implying that ERK1/2 signalling is unlikely to be instrumental in the maintenance of GNAQQ209P-driven UMs.

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.

Background: Cancer is currently the second leading cause of death globally.There is much uncertainty regarding the comparative risks of new-onset overall cancer and pre-specified cancer for Type 2 diabetes mellitus (T2DM) patients on sodium-glucose cotransporter 2 inhibitors (SGLT2I) versus DPP4I.Methods: This population-based cohort study patients included patients who were diagnosed with T2DM and administered either SGLT2 or DPP4 inhibitors between 1 January 2015 and 31 December 2020 in public hospitals of Hong Kong.Results: This study included 60,112 T2DM patients (mean baseline age:62.1 ± 12.4 years, male: 56.36%), of which 18,167 patients were SGLT2I users and 41,945 patients were dipeptidyl peptidase 4 inhibitor (DPP4I) users. Multivariable Cox regression found that SGLT2I use was associated with lower risks of all-cause

Background: There is much uncertainty regarding the comparative risks of cancer for T2DM patients on SGLT2I versus DPP4I. Methods: This population-based cohort study patients included T2DM patients who were administered with either SGLT2I or DPP4I between January 1st, 2015, to December 31st, 2020 in Hong Kong. Results: Amongst 60112 T2DM patients (mean baseline age: 62.1+/-12.4 years, male: 56.36%), 18167 patients were SGLT2I users and 41945 patients were DPP4I users. Multivariate cox regression analysis revealed that SGLT2I usage was associated with a decreased risk of all-cause mortality (HR:0.92; 95%CI:0.84-0.99; P=0.04), cancer-related mortality (HR:0.58; 95%CI:0.42-0.80; P≤0.001) and a 30% risk reduction of new-onset overall cancer (HR:0.70; 95%CI:0.59-0.84; P≤0.001). Dapagliflozin and ertugliflozin both demonstrated superiority in relation to new-onset cancer development, with the former demonstrating a lowered risk of breast cancer (HR:0.48; 95%CI:0.27-0.83; P=0.001). Conclusion: SGLT2I was associated with lower risk of all-cause mortality, cancer-related mortality and new-onset overall cancer compared to DPP4I.

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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...

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