Microglia extracellular traps in Oreochromis niloticus infected with Weissella cibaria

Expression of two CD83 homologs in macrophage subpopulations isolated from the brain and kidney of ginbuna crucian carp

There are numerous fish diseases that affect the central nervous system. However, few studies have investigated the immune cells and immunological responses of fish brains. Meanwhile, microglial cells, as the brain's first line of defense, play a vital role in neuroimmunology. Furthermore, CD83 is a co-stimulatory protein that regulates immunological responses and the activation of dendritic cells and macrophages. Although CD83 expression has been linked to the initial activation of microglia in various disease scenarios in mammals, its role in teleost microglial biology remains unclear. In a recent investigation, we discovered that Ginbuna crucian carp (Gb) contains two CD83 homologs (GbCD83 and GbCD83-L). In this study, we used modified procedures of mouse-based macrophage culture from the brain and kidney to identify that GbCD83-L is highly expressed by the brain microglia-like cells and kidney-resident macrophages (KRMs) at both the protein and gene levels. Interestingly, GbCD83-L was considerably elevated in the microglia-like cells and KRMs after 24 h of lipopolysaccharide stimulation. These findings provide the first evidence of CD83 as a potential marker for active microglia and KRMs in teleosts, thus making it a crucial regulator in fish neuroimmunology and a candidate for future immunomodulatory applications in aquaculture.

Macrophages coordinate immune response to laser-induced injury via extracellular traps

BACKGROUND

Retinal degeneration results from disruptions in retinal homeostasis due to injury, disease, or aging and triggers peripheral leukocyte infiltration. Effective immune responses rely on coordinated actions of resident microglia and recruited macrophages, critical for tissue remodeling and repair. However, these phagocytes also contribute to chronic inflammation in degenerated retinas, yet the precise coordination of immune response to retinal damage remains elusive. Recent investigations have demonstrated that phagocytic cells can produce extracellular traps (ETs), which are a source of self-antigens that alter the immune response, which can potentially lead to tissue injury.

METHODS

Innovations in experimental systems facilitate real-time exploration of immune cell interactions and dynamic responses. We integrated in vivo imaging with ultrastructural analysis, transcriptomics, pharmacological treatments, and knockout mice to elucidate the role of phagocytes and their modulation of the local inflammatory response through extracellular traps (ETs). Deciphering these mechanisms is essential for developing novel and enhanced immunotherapeutic approaches that can redirect a specific maladaptive immune response towards favorable wound healing in the retina.

RESULTS

Our findings underscore the pivotal role of innate immune cells, especially macrophages/monocytes, in regulating retinal repair and inflammation. The absence of neutrophil and macrophage infiltration aids parenchymal integrity restoration, while their depletion, particularly macrophages/monocytes, impedes vascular recovery. We demonstrate that macrophages/monocytes, when recruited in the retina, release chromatin and granular proteins, forming ETs. Furthermore, the pharmacological inhibition of ETosis support retinal and vascular repair, surpassing the effects of blocking innate immune cell recruitment. Simultaneously, the absence of ETosis reshapes the inflammatory response, causing neutrophils, helper, and cytotoxic T-cells to be restricted primarily in the superficial capillary plexus instead of reaching the damaged photoreceptor layer.

CONCLUSIONS

Our data offer novel insights into innate immunity's role in responding to retinal damage and potentially help developing innovative immunotherapeutic approaches that can shift the immune response from maladaptive to beneficial for retinal regeneration.

Grass carp Il-2 promotes neutrophil extracellular traps formation via inducing ROS production and autophagy in vitro

Interleukin (IL)-2 has been reported to regulate neutrophil functions in humans, mice, pigs and chicken although it is a key regulator of T cells. Consistently, we found that grass carp (Ctenopharyngodon idellus) interleukin-2 (gcIl-2) is capable of modulating the antimicrobial activities of neutrophils via regulating granzyme B- and perforin-like gene expression in our previous study. In the present study, stimulation of gcIl-2 on neutrophil extracellular traps (NETs) formation in grass carp neutrophils was demonstrated by detecting free DNA release, histone H3 citrullination and morphological changes of the cells. Further investigation revealed that reactive oxygen species (ROS) production from NADPH oxidase but not mitochondria was involved in NETosis induced by gcIl-2. Aside from ROS, autophagy was disclosed to be indispensable for NETosis induced by gcIl-2. These converging lines of evidence suggested that fish Il-2 could induce NETs formation via NADPH oxidase-derived ROS- and autophagy-dependent pathways in fish species which is evolutionarily conserved with that in mammals. It is noteworthy that these two pathways did not interplay with each other in Il-2-stimulated NETosis. The mechanisms governing autophagy induced by Il-2 were also explored in the present study, showing that Il-2 modulated the action of high mobility group box 1 (HMGB1) protein to stimulate autophagy, leading to NETs formation in fish neutrophils. These results provided a new insight to the function of Il-2 in fish neutrophils, and a clue about the regulation of NETosis in the lower vertebrates.

ß1-adrenergic blockers preserve neuromuscular function by inhibiting the production of extracellular traps during systemic inflammation in mice

Severe inflammation via innate immune system activation causes organ dysfunction. Among these, the central nervous system (CNS) is particularly affected by encephalopathies. These symptoms are associated with the activation of microglia and a potential infiltration of leukocytes. These immune cells have recently been discovered to have the ability to produce extracellular traps (ETs). While these components capture and destroy pathogens, deleterious effects occur such as reduced neuronal excitability correlated with excessive ETs production. In this study, the objectives were to determine (1) whether immune cells form ETs in the CNS during acute inflammation (2) whether ETs produce neuromuscular disorders and (3) whether an immunomodulatory treatment such as β1-adrenergic blockers limits these effects. We observed an infiltration of neutrophils in the CNS, an activation of microglia and a production of ETs following lipopolysaccharide (LPS) administration. Atenolol, a β1-adrenergic blocker, significantly decreased the production of ETs in both microglia and neutrophils. This treatment also preserved the gastrocnemius motoneuron excitability. Similar results were observed when the production of ETs was prevented by sivelestat, an inhibitor of ET formation. In conclusion, our results demonstrate that LPS administration increases neutrophils infiltration into the CNS, activates immune cells and produces ETs that directly impair neuromuscular function. Prevention of ETs formation by β1-adrenergic blockers partly restores this function and could be a good target in order to reduce adverse effects in severe inflammation such as sepsis but also in other motor related pathologies linked to ETs production.

The knowns and many unknowns of CNS immunity in teleost fish

Many disease agents infect the central nervous system (CNS) of teleost fish causing severe losses for the fish farming sector. Yet, neurotropic fish pathogens remain poorly documented and immune responses in the teleost CNS essentially unknown. Previously thought to be devoid of an immune system, the mammalian CNS is now recognized to be protected from infection by diverse immune cells that mostly reside in the meningeal lymphatic system. Here we review the current body of work pertaining immune responses in the teleost CNS to infection. We identify important knowledge gaps with regards to CNS immunity in fish and make recommendations for rigorous experimentation and reporting in manuscripts so that fish immunologists can advance this burgeoning field.

Induction and characterization of extracellular traps by gilthead seabream (Sparus aurata L.) head-kidney leucocytes

The aim of this study was the induction and characterization of extracellular traps (ETs) produced by gilthead seabream (Sparus aurata L.) head-kidney leucocytes. The cells were incubated several times (10, 30, 60, 120, and 180 min) with different concentrations of the stimulants diluted in RPMI-1640 culture medium: RPMI-1640 (control), β-glucan from Saccharomyces cerevisiae (BG, 0-400 μg mL^-1), lipopolysaccharide from Escherichia coli (LPS, 0-10 μg mL^-1), calcium ionophore A23187 (CaI, 0-5 μg mL^-1), Phorbol 12-myristate 13-acetate (PMA, 0-1000 ng mL^-1) and polyinosinic-polycytidylic acid sodium salt (Poly I:C, 0-200 μg mL^-1). BG, LPS and CaI exerted only weak stimulatory activity, while PMA and poly I:C exerted a potent one. After stimulation of the leucocytes, ETs structures were quantified and visualised through staining of the chromatin with nucleic acid-specific dyes and immunocytochemical probing of characteristic proteins expected to decorate the structure. ETs structures had DNA and myeloperoxidase. The ETs morphology was studied by light and scanning electron microscopy. These data confirm that seabream leucocytes form ETs with different morphological properties, depending on the used stimulant. These results will be the basis for new studies to analyse the implication of this mechanism in fish immunity. All this new knowledge will have its application in fish farms when we learn to manipulate the innate immune response in order to mitigate microbial infections.

Molecular Characterization, Expression, Evolutionary Selection, and Biological Activity Analysis of CD68 Gene from Megalobrama amblycephala

CD68 is a highly glycosylated transmembrane glycoprotein that belongs to the lysosome-associated membrane glycoprotein family and is involved in various immune processes. In this study, Megalobrama amblycephala CD68 (MaCD68) was cloned and characterized, and its expression patterns and evolutionary characteristics were analyzed. The coding region of MaCD68 was 987 bp, encoding 328 amino acids, and the predicted protein molecular weight was 34.9 kDa. MaCD68 contained two transmembrane helical structures and 18 predicted N-glycosylation sites. Multiple sequence alignments showed that the MaCD68 protein had high homology with other fish, and their functional sites were also highly conserved. Phylogenetic analysis revealed that MaCD68 and other cypriniformes fish clustered into one branch. Adaptive evolution analysis identified several positively selected sites of teleost CD68 using site and branch-site models, indicating that it was under positive selection pressure during evolution. Quantitative real-time reverse transcription polymerase chain reaction analysis showed that MaCD68 was highly expressed in the head kidney, spleen, and heart. After Aeromonas hydrophila infection, MaCD68 was significantly upregulated in all tested tissues, peaking at 12 h post-infection (hpi) in the kidney and head kidney and at 120 hpi in the liver and spleen, suggesting that MaCD68 participated in the innate immune response of the host against bacterial infection. Immunohistochemical and immunofluorescence analyses also showed that positive signals derived from the MaCD68 protein were further enhanced after bacterial and lipopolysaccharide treatment, which suggested that MaCD68 is involved in the immune response and could be used as a macrophage marker. Biological activity analysis indicated that recombinant MaCD68 (rMaCD68) protein had no agglutination or bactericidal effects on A. hydrophila but did have these effects on Escherichia coli. In conclusion, these results suggest that MaCD68 plays a vital role in the immune response against pathogens, which is helpful in understanding the immune responses and mechanisms of M. amblycephala.

Tilapia Lake Virus-Induced Neuroinflammation in Zebrafish: Microglia Activation and Sickness Behavior

In mammals, the relationship between the immune system and behavior is widely studied. In fish, however, the knowledge concerning the brain immune response and behavioral changes during brain viral infection is very limited. To further investigate this subject, we used the model of tilapia lake virus (TiLV) infection of zebrafish (Danio rerio), which was previously developed in our laboratory. We demonstrated that TiLV persists in the brain of adult zebrafish for at least 90 days, even when the virus is not detectable in other peripheral organs. The virions were found in the whole brain. During TiLV infection, zebrafish displayed a clear sickness behavior: decreased locomotor activity, reduced food intake, and primarily localizes near the bottom zone of aquaria. Moreover, during swimming, individual fish exhibited also unusual spiral movement patterns. Gene expression study revealed that TiLV induces in the brain of adult fish strong antiviral and inflammatory response and upregulates expression of genes encoding microglia/macrophage markers. Finally, using zebrafish larvae, we showed that TiLV infection induces histopathological abnormalities in the brain and causes activation of the microglia which is manifested by changes in cell shape from a resting ramified state in mock-infected to a highly ameboid active state in TiLV-infected larvae. This is the first study presenting a comprehensive analysis of the brain immune response associated with microglia activation and subsequent sickness behavior during systemic viral infection in zebrafish.