Biology subjects

Condliffe, A. M.

Publications and source records attributed to Condliffe, A. M..

4 recordsLinked to original sources

bioRxiv2024

Pulses of Class I PI3kinase activity identify the release and recapture of prey from neutrophil phagosomes

Class I PI3kinases coordinate the delivery of microbicidal effectors to the phagosome by forming the phosphoinositide lipid second messenger, phosphatidylinositol (3, 4, 5)-trisphosphate (PIP3). However, the dynamics of PIP3 in neutrophils during a bacterial infection are unknown. We have therefore developed an in vivo, live zebrafish infection model that enables visualisation of dynamic changes in Class 1 PI3kinases (PI3K) signalling on neutrophil phagosomes in real-time. We have identified that on approximately 12% of neutrophil phagosomes PHAkt-eGFP, a reporter for Class 1 PI3K signalling, re-recruits in pulsatile bursts. This phenomenon occurred on phagosomes containing structurally and morphologically distinct prey, including Staphylococcus aureus and Mycobacterium abscessus, and was dependent on the activity of the Class 1 PI3K isoform, PI3kinase {gamma}. Detailed imaging suggested that pulsing phagosomes represent neutrophils transiently reopening and reclosing phagosomes. This finding challenges the concept that phagosomes remain closed after prey engulfment and we propose that neutrophils occasionally use this alternative pathway of phagosome maturation to release phagosome contents and/or to restart phagosome maturation if digestion has stalled.

cell biology↗

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↗

bioRxiv2019

Macrophages utilize mitochondrial fission to enhance mROS production during responses to Streptococcus pneumoniae

Immunometabolism and regulation of mitochondrial reactive oxygen species (mROS) are critical determinants of the immune effector phenotype of differentiated macrophages. Mitochondrial function requires dynamic fission and fusion, but whether effector function is associated with altered dynamics during bacterial responses is unknown. We show that macrophage mitochondria undergo fission after 12 h of progressive ingestion of live Streptococcus pneumoniae (pneumococci). Fission is associated with progressive reduction in oxidative phosphorylation but increased mROS generation. Fission is enhanced by mROS production, PI3K{gamma} signaling and by cathepsin B, but not by inflammasome activation or IL-1{beta} generation. Reduced fission following PI3K{gamma} or cathepsin B inhibition is associated with reduced mROS generation and bacterial killing. Fission is associated with Parkin recruitment to mitochondria, but not mitophagy. Fission occurs upstream of apoptosis induction and independently of caspase activation. During macrophage innate responses to live bacteria mitochondria shift from oxidative phosphorylation and ATP generation to mROS production and microbicidal responses with a progressive shift towards mitochondrial fission.

immunology↗

bioRxiv2018

PI3Kδ hyper-activation promotes the development of B cells that exacerbate Streptococcus pneumoniae infection in an antibody-independent manner

Streptococcus pneumoniae is a major cause of pneumonia and a leading cause of death world-wide. Antibody-mediated immune responses can offer protection against repeated exposure to S. pneumoniae, yet vaccines only offer partial protection. Patients with Activated PI3K{delta} Syndrome (APDS) are highly susceptible to S. pneumoniae. We generated a conditional knockin mouse model of this disease and identified a CD19+B220- B cell subset that is induced by PI3K{delta} signaling, is resident in the lungs, and which promotes increased susceptibility to S. pneumoniae during the early phase of infection via an antibody-independent mechanism. We show that an inhaled PI3K{delta} inhibitor improves survival rates following S. pneumoniae infection in wild-type mice and in mice with activated PI3K{delta}. These results suggest that a subset of B cells in the lung can promote the severity of S. pneumoniae infection, representing a novel therapeutic target.

immunology↗