Biology subjects

Hammond, F. R.

Publications and source records attributed to Hammond, F. R..

4 recordsLinked to original sources

bioRxiv2023

Candida albicans suppression of neutrophil reactive nitrogen species is rescued by host Hif-1alpha in vivo

Candida albicans is a human commensal that can cause life-threatening invasive infection in immunocompromised individuals. Human immunity to C. albicans infection is thought to be largely dependent on neutrophil reactive oxygen and nitrogen species (ROS/RNS) generation by neutrophils. Despite this, our understanding of innate immune killing and escape by C. albicans is primarily studied in macrophages and the precise mechanisms of evasion are unclear in neutrophils. Here we sought to determine the importance of neutrophil reactive nitrogen species (RNS) production during C. albicans infection in vivo. Using a zebrafish model, we found that C. albicans rapidly downregulated neutrophil RNS below basal levels during the first day post infection, a time at which neutrophil RNS is upregulated in bacterial infections as an important host-defense mechanism, indicating fungal evasion of host neutrophils. We confirmed downregulation of RNS in human primary neutrophils and with clinical Candida spp. isolates, including emerging human pathogens C. auris and C. glabrata. Using a zebrafish arginase 2 transgenic line and a C. albicans car1{Delta} mutant, we show that both host and fungal arginase contribute the reduction in neutrophil RNS. Despite pathogen downregulation, upregulation of neutrophil RNS via Hypoxia inducible factor (Hif)-1 stabilisation, was sufficient to improve C. albicans infection survival, dependent on the presence of neutrophils and Nitric oxide synthase 2 (Nos2). Finally, restoration of neutrophil RNS, via Hif-1 stabilisation, was synergistic with clinically relevant antifungal treatment, increasing survival and clearance of C. albicans infections. Together, these data demonstrate that restoration of the neutrophil RNS response in C. albicans infection improves infection outcomes, highlighting the potential of targeting Hif-1 and RNS in host directed therapies against fungal infections.

immunology↗

bioRxiv2023

Tribbles1 and Cop1 cooperate to protect the host during in vivo mycobacterial infection

Tuberculosis is a major global health problem and is one of the top 10 causes of death worldwide. There is a pressing need for new treatments that circumvent emerging antibiotic resistance. Mycobacterium tuberculosis parasitises macrophages, reprogramming them to establish a niche in which to proliferate, therefore macrophage manipulation is a potential host-directed therapy if druggable molecular targets could be identified. The pseudokinase Tribbles1 (Trib1) regulates multiple innate immune processes and inflammatory profiles making it a potential drug target in infections. Trib1 controls macrophage function, cytokine production and macrophage polarisation. Despite wide-ranging effects on leukocyte biology, data exploring the roles of Tribbles in infection in vivo are limited. Here, we identify that human Tribbles 1 is expressed in monocytes and is upregulated at the transcript level after stimulation with mycobacterial antigen. To investigate the mechanistic roles of Tribbles in the host response to mycobacteria in vivo, we used a zebrafish Mycobacterium marinum (Mm) infection tuberculosis model. Zebrafish Tribbles family members were characterised and shown to have substantial mRNA and protein sequence homology to their human orthologues. trib1 overexpression was host-protective against Mm infection, reducing burden by approximately 50%. Conversely, trib1 knockdown exhibited increased infection. Mechanistically, trib1 overexpression significantly increased the levels of pro-inflammatory factors il-1{beta} and nitric oxide. The host-protective effect of trib1 was found to be dependent on the E3 ubiquitin kinase Cop1. These findings highlight the importance of Trib1 and Cop1 as immune regulators during infection in vivo and suggest that enhancing macrophage TRIB1 levels may provide a tractable therapeutic intervention to improve bacterial infection outcomes in tuberculosis.

immunology↗

bioRxiv2022

An arginase 2 promoter transgenic illuminates anti-inflammatory signalling in zebrafish

The innate immune response to inflammatory stimuli must be finely balanced to produce an appropriate pro-inflammatory response while allowing a subsequent return to homeostasis. In recent years, in vivo transgenic zebrafish models have shed light on the temporal regulation of the pro-inflammatory innate response to immune challenges. However, until now, there have been no zebrafish transgenic models of anti-inflammatory signalling. We compared existing expression data of arginase genes in zebrafish neutrophils and macrophages, strong candidates for an anti-inflammatory marker, and identified that arginase 2 is the most highly expressed Arginase in zebrafish immune cells. We developed an arginase 2 (arg2) bacterial artificial chromosome (BAC) transgenic line, TgBAC(arg2:eGFP)sh571, driving GFP expression under the control of the arg2 promoter. We show that, under resting conditions, arg2:GFP is expressed in ionocytes, matching the in situ hybridisation pattern. Upon immune challenge by injury, bacterial and fungal insults, arg2:GFP is predominantly expressed in neutrophils at early timepoints post-insult. Later in infections, arg2:GFP is expressed in cells associated with foci of infection (including neutrophils and macrophages), alongside liver expression. Our data indicate that arginase 2 is predominantly expressed in neutrophils after immune challenge and suggest that anti-inflammatory signals coincide with pro-inflammatory signals during early wound and infection responses.

immunology↗

bioRxiv2020

Differential response of macrophages and neutrophils to trypanosome infections in zebrafish: occurrence of foamy macrophages

A tightly regulated innate immune response to trypanosome infections is critical to strike a balance between parasite control and inflammation-associated pathology. In the present study, we make use of the recently established Trypanosoma carassii infection model in larval zebrafish to study the early response of macrophages and neutrophils to trypanosome infections in vivo. We consistently identified high- and low-infected individuals and were able to simultaneously characterize their differential innate response. Not only did macrophage and neutrophil number and distribution differ between the two groups, but also macrophage morphology and activation state. Exclusive to high-infected zebrafish, was the appearance of macrophages rich in lipid droplets, confirmed to be foamy macrophages and characterized by a strong pro-inflammatory profile. Altogether, we provide an in vivo characterization of the differential response of macrophage and neutrophil to trypanosome infection and identify foamy macrophages as potentially associated with an exacerbated immune response and susceptibility to the infection. To our knowledge this is the first report of the occurrence of foamy macrophages during an extracellular trypanosome infection.

microbiology↗