Local oxidised phospholipids within the pleural cavity: fuelling macrophage response during inflammation?

Inflammation as part of the immune response is the body's normal reaction to injury & infection. Inflammation is related to many life threatening conditions & is particularly associated with respiratory problems. In our chests, the pleural space that exists between the ribcage & lungs is lined by specialised cells that secrete small amounts of pleural fluid. Pleural fluid contains immune cells, in particular large numbers of cells known as macrophages or 'big-eaters'. Pleural macrophages provide a significant layer of protection against external pathogens, allergens & carcinogens that enter the body via the lungs.

Cholesterol is an essential fat required during normal physiology, too much cholesterol can be toxic and so production, storage & movement of cholesterol around the body is tightly regulated. Lipo-proteins are mixtures of fats & cholesterol packaged up for delivery around the body. Macrophages can use fats as a fuel source and are able to obtain them via uptake of lipo-proteins present within bodily fluids.

Antibodies are proteins that can recognise & bind infectious & damage associated molecules often resulting in their clearance from the body. We have identified that during inflammation related to an allergic-like response in the pleural space there are increased levels of antibodies that recognise lipo-proteins and the macrophages at the site of inflammation begin to make their own cholesterol.

In this project we want to determine whether lipo-proteins are produced locally within the pleural space in the absence, as well as in the presence, of different types of lung inflammation. We will aim to determine what induces their production and if recognition & uptake of these lipid species controls the normal function of pleural macrophages. Are macrophages 'eating' these lipids in order to make energy? Do the lipids damage the cells? Are the lipids required for macrophages to divide? Do antibodies modify the ability of macrophages to detect these lipids? Does blockade of macrophage lipid detection turn on cellular cholesterol synthesis? What is the cholesterol used for?

Solutions to these questions will lead to profound changes in our understanding of the inflammatory processes associated with respiratory disease as well as offering new targets for both therapeutic intervention and diagnostics.

The pleural cavity is formed by a double layer of mesothelial membranes which encompass the lungs; mesothelial cells secrete pleural fluid which provides a niche for the accumulation of immune cells predominated by large cavity macrophages (LCM) & innate-like B cells (IBC). Pleural LCM provide a significant layer of protection against external pathogens, allergens & carcinogens that enter the body via the lungs. Energy & lipid usage in pleural LCM is not well understood. Oxidised phospholipids (OxPLs) are coming to the fore as regulators of metabolism, where in the context of classical inflammatory stimuli exposure results in induction of a macrophage hyper-metabolic state; the role of oxPL on LCM function during type-2 inflammation is unknown. Lipid peroxidation occurs due to the presence of intracellular oxidants during normal metabolic processes (fatty acid oxidation), or as a result of inflammation (via ROS). Oxidation specific epitopes such as those present within oxLDL, an oxPL mixture, can be recognised by IgM. Fat associated lymphoid clusters (FALCs) are key sites of local IgM secretion during pleural infection & inflammation.

Murine models of global secretory IgM & macrophage CD36 deficiency will be used to determine the role of oxPL recognition in modulation of the phenotypic & metabolic profile of LCM & IBC responses during diverse models of type-1 & type-2 pleural inflammation. Sources & cellular uses of oxPL will be determined via investigations into lung, FALC, & pleural fluid in vitro, in vivo & within human pleural effusate. This project has potential to reveal novel metabolic targets for modulation of pleural immune cell phenotype & function enabling design of therapeutics to improve patient outcomes during lung disease.