Tracking protein-protein interactions in innate immune cells. Left: Surface expression of C5aR (green) on unstimulated human macrophages. Centre: Activation of C5aR with inflammatory protein C5a induces internalisation and formation of endosome with Rab5a (red). Right: Genetic deletion of Rab5a blocks C5aR internalisation and downstream inflammatory responses.
Credit: Kai-Chen Wu
“Visualizing both a surface protein on human innate immune cells and key signalling proteins inside the cells allows us to understand how a protein in the blood causes inflammation in an organism.”
Innate immune cells provide the first line of defence against infection and injury. They include mast cells, eosinophils, monocytes, macrophages, neutrophils, dendritic cells and Natural Killer (NK) cells. Some innate immune cells reside in our tissues and are exposed to the environment, others are recruited to tissues in response to infection or injury. Imaging CoE researchers also study epithelial cells that form a physical, chemical and immunological barrier on tissue surfaces (skin, lungs, gastrointestinal tract, organs, blood vessels) exposed to the environment. These cells are the first point of contact with infectious organisms and environmental stress. Collectively, they monitor changes to tissues and maintain them in a healthy state, quickly identifying threats and eliminating them along with damaged cells.
PROF. DAVID FAIRLIE
AT A GLANCE
Innate immune cells respond to pathogens or cancer cells using surface proteins as receptors. How their interactions cause signalling, cell activation and immune responses remains poorly understood. Imaging CoE researchers have developed novel compounds for modulating receptors and proteins and used molecular and microscopy imaging to track important signalling events in innate immune cells during inflammation. This work has allowed simultaneous tracking of the movement, destinations and fates of key activating molecules outside cells, key receptor proteins on the cell surface, and coupling to signalling proteins inside cells. This has allowed the Imaging CoE to develop new approaches for mapping innate immune cells during different phases of their responses to infectious and non-infectious stimuli in cancer, metabolic and inflammatory disease.
- Developed fluorescent ligands for imaging the activation or inhibition of inflammation-related proteins (GPCRs) involved in innate immune responses to microbes, tumours or chemicals.
- Imaged the motility and migration of innate immune cells and cancer cells in vitro and in vivo.
- Discovered, mapped and selectively blocked signalling pathways that mediate innate immunity.
- Discovered links between surveillance, metabolism and inflammation in innate immunity.
- Targeted specific proteins on macrophages and mast cells that mediate immune responses.
- Imaged dendritic cells to study molecules that alter their immunological properties.
Linking inflammation to arthritis
A group of proteins (HDACs) present in immune cells are known to be important contributors to inflammatory conditions such as arthritis. HDACs are key regulatory proteins controlling immune responses in innate immune cells (macrophages, mast cells) and are found to be overexpressed in human arthritis patients. Imaging CoE researchers have used key techniques in immunology, molecular imaging and 3D micro-computed tomography to investigate immunological roles of HDACs in arthritis. Of potential therapeutic interest, novel inhibitors of HDACs decreased inflammatory markers and improved the damaging arthritic conditions in rats. These findings offer potential prospects of future therapies that modulate HDACs to achieve beneficial clinical outcomes.
3D tomography of knee joints from rats administered with novel HDAC inhibitor. Healthy knee joint (top) compared to the swollen arthritic knee (centre) and treated arthritic knee (bottom). Image Credit: Eunice Poon
Innate immune signalling
Proteases are important signalling molecules in innate immune responses and many of them activate a surface protein called a protease activated receptor (PAR) on immune cells and cancer cells. The development of novel fluorescent ligands and receptors has led to a better understanding of intracellular signalling in immune cells versus cancer cells. These compounds prevent PAR from activating downstream signalling inflammatory pathways in immune cells and cancer cells. This in turn blocks the motility and invasion of cancer cells to different sites.