The role of leukotrienes and eosinophil cationic protein in acute respiratory syncytial virus bronchiolitis.

The Respiratory Syncytial Virus (RSV) is the leading cause of lower respiratory tract infection in infants and by 2.5 to 3 years of age most children have been infected with approximately 1-2% of all infected infants requiring hospital admission. Both immunologic and nonimmunologic factors have been implicated in the susceptibility to symptomatic RSV-induced disease although most attention has been directed towards host responses and their role in the pathogenesis of the associated airway obstruction. Although the mechanisms and host responses associated with symptomatic RSV disease are not yet clear, products more usually associated with allergic inflammation such as cysteinyl leukotrienes and eosinophil cationic protein have been detected in airway secretions of affected infants. Leukotrienes are synthesized through the 5-lipoxygenase pathway from the arachidonic acid which is released from the phospholipids forming the membrane of activated cells. They are potent inflammatory mediators and can cause increased secretion of mucus, airway oedema, bronchoconstriction, airway obstruction. Eosinophil cationic protein is a unique protein from the noncore matrix of the eosinophil cells. Eosinophils and eosinophil mediators are involved in the process of airway obstruction found in many common paediatric pulmonary disorders. The potential role of leukotrienes and eosinophil cationic protein in RSV disease, especially bronchiolitis, are reviewed.