<prompt> Which of the following statements concerning alveolar macrophages is true?They secrete a1-antitrypsin.They secrete elastase.They originate from blood neutrophilsThey may play a role in causing hyaline membrane disease  <response>: Alveolar macrophages secrete elastase. Normally, a1-antitrypsin, a serum protein, interacts with elastase, thereby protecting the lung against damage that may lead to emphysema. 