Leukotriene B4 is a pro-inflammatory mediator synthesised in myeloid cells from arachidonic acid. Synthesis is catalysed by 5-lipoxygenase and leukotriene A4 hydrolase and is increased by inflammatory mediators including endotoxin, complement fragments, tumor necrosis factor and interleukins. A nuclear membrane protein, 5-lipoxygenase activating protein, is an essential co-factor for 5-lipoxygenase. Leukotriene B4 induces recruitment and activation of neutrophils, monocytes and eosinophils. It also stimulates the production of a number of proinflammatory cytokines and mediators indicating an ability to augment and prolong tissue inflammation. Elevated levels of leukotriene B4 have been found in a number of inflammatory diseases and levels are related to disease activity in some of these. Initial data from pharmacological inhibition studies support a role for leukotriene B4 in the pathogenesis of neutrophil mediated tissue damage, and treatments which reduce its production or block its effects may prove beneficial in neutrophil mediated inflammatory diseases.

There has been much recent interest in the role of the vitamin D axis in lung disease, which includes vitamin D, vitamin D receptor (VDR) and vitamin D-binding protein (VDBP; also known as Gc-globulin). VDBP is a serum protein which has immunomodulatory functions relevant in the lung, predominantly relating to macrophage activation and neutrophil chemotaxis. Variations within its gene are also associated with airways disease, implying a role for the protein product in pathogenesis. Thus far the majority of evidence relates to chronic obstructive pulmonary disease (COPD), but is scant in other airways diseases, such as asthma and bronchiectasis. VDBP also acts as a scavenger protein to clear extracellular G-actin released from necrotic cells, which may be of relevance in severe lung infections and acute lung injury. Vitamin D protects against the development of cancer and tuberculosis, although optimal levels are unknown. The majority of circulating vitamin D is bound to VDBP, and its uptake into cells occurs in both bound and unbound forms, which suggests the role of VDBP warrants further study in these conditions as well. This article reviews the evidence of the role VDBP and its gene (GC) in a range of lung diseases, including asthma, COPD and tuberculosis.

An imbalance between neutrophil proteases and the surrounding antiproteases is critical in the normal functioning of the neutrophil. Enzyme activity is of importance in cell migration and may play a role in some beneficial aspects of host defense. However, when persistent or excessive this imbalance can be detrimental and (even in the absence of antiprotease deficiency) central to most of the pathogenic processes in COPD. Understanding of these complex relationships that alter a beneficial host defense response to a destructive one will be critical in the development of long-term therapeutic strategies. Stockley RA. Neutrophils and protease/antiprotease imbalance.

Background: Sputum analysis is used increasingly to assess airway inflammation in patients with chronic obstructive pulmonary disease, including those with chronic bronchitis and bronchiectasis. However, it is not known whether dithiothreitol (DTT), a reducing mucolytic agent regularly used to homogenise sputum, affects the detection of inflammatory mediators in the sputum soluble phase from such patients. Methods: Thirty two spontaneous sputum samples were collected from 13 patients with chronic bronchitis and 17 with bronchiectasis. An aliquot from each sample was treated with either freshly prepared 0.1% DTT plus normal saline (NaCl) or NaCl alone, then ultracentrifuged to obtain the sputum sol phase. Interleukin (IL)-1β, IL-6, IL-8, leukotriene B 4 (LTB 4 ), secretory leukoprotease inhibitor (SLPI), alpha-1-antitrypsin (α 1 -AT), and tumour necrosis factor alpha (TNFα) were measured by ELISA, and neutrophil elastase (NE) and myeloperoxidase (MPO) by chromogenic substrate assay. The effect of DTT on the detection of assay standards was also determined. Results: Median levels of IL-1β, IL-6, IL-8, SLPI, and NE were similar in the DTT and NaCl treated samples. There was a significant reduction in median (IQR) levels of detectable TNFα (0.07 (0.00-0.47) pM v 0.90 (0.06-6.98) pM, p<0.001), LTB 4 (1.67 (1.31-2.64) nM v 2.29 (0.95-4.22) nM, p<0.05) and MPO (0.00 (0.00-0.00) mg/l v 4.48 (0.00-33.66) mg/l, p<0.001) and a small increase in the median α 1 -AT concentration (0.05 (0.03-0.08) nM v 0.03 (0.02-0.08) nM, p<0.01) in the DTT treated samples. DTT had no effect on the assay standards for IL-1β, IL-8 or TNFα, but at higher concentrations it did affect IL-6, SLPI, NE, and LTB 4 standards (43%, 70%, 76% and 643% of control value for top standard, respectively) and at all concentrations DTT completely abolished MPO activity. Conclusions: Sputum processing with DTT significantly reduces the detectable concentration of TNFα, LTB 4 and MPO, and produces a small but significant increase in median α 1 -AT levels. To avoid this problem we recommend that an untreated aliquot of sputum be retained for cytokine analysis, unless the assay has been specifically validated.

No abstract