The Laboratory Investigation of Mediators and Inflammatory Cells in Asthma and Rhinitis

Many of the clinical and pathological features of asthma and rhinitis can be explained in part on the basis of the mode of action of various mast-cell associated mediators and associated agents as well as products derived from inflammatory cells. The methodology is now available for accurately identifying a number of preformed and newly-formed mediators in a variety of body fluids such as nasal secretions and the blood.

Most of the studies to date have involved measurements of histamine and the high molecular weight neutrophil chemotactic activity whereas more recently assays for the lipoxygenase products, LTB₄ and LTC₄, have been developed. In addition to specific allergen, non-specific stimuli such as exercise- and ‘fog’-induced asthma also appear to be associated with mediator release, suggesting that mediator cells such as mast cells respond to immunologic as well as non-immunologic triggers.

Mediators can be broadly divided into agents which have a direct effect on bronchial tissue and those which recruit and activate secondary inflammatory cells. These cell types include neutrophils, eosinophils and mononuclear cells. Particular attention is given to the eosinophil as a major pro-inflammatory cell in asthma and possibly rhinitis. Equally, the macrophage may play a major role in the maintenance of the eosinophil-rich environment. The relationship between inflammation and non-specific hyperreactivity is also the subject of intense current investigation.