Plasma complement changes during bronchospasm provoked in asthmatic patients*

Summary Two different groups of asthmatic patients were studied. The first group of seven reagin‐mediated asthmatic patients underwent bronchial inhalation challenges with skin test positive antigen (STPA), skin test negative antigen (STNA) and methacholine. Three patients undergoing inhalation challenge with STPA showed a drop in plasma complement. In this group the drop in plasma complement was found only when the patient was challenged with STPA but not with STNA or methacholine. The second group consisted of seventeen patients, seven of whom were intolerant of aspirin (ASA) and ten asthmatic patients who experienced no untoward effects to ASA. The second group of seventeen patients was challenged with oral ASA. Venous blood samples collected during the challenges, showed a decrease in plasma complement in five patients intolerant to ASA. The ASA intolerant asthmatic patients were challenged also with either Maalox® or sodium salicylate. Only patients who ingested sodium salicylate showed a decrease in plasma complement. Activation of the alternative pathway was demonstrated in some patients. These studies demonstrated that complement activation occurred during STPA or aspirin challenges in asthmatic individuals. The role of the complement system is not clear, but it may participate in some of the pathogenetic mechanisms regulating bronchospasm through the mediations of its split products.