A peptide from alveolar macrophages that releases neutrophil enzymes into the lungs in patients with the adult respiratory distress syndrome.

A monoclonal antibody has been made to a peptide that is released by human alveolar macrophages. This enzyme-releasing peptide (ERP) causes neutrophils to secrete azurophilic granule enzymes. Normal subjects, patients with pulmonary fibrosis, and patients with sarcoidosis had similar concentrations of this peptide in their bronchoalveolar lavage fluids. However, patients with the adult respiratory distress syndrome (ARDS) had about 2.7 times higher concentrations in their lavage fluids. The enzyme-releasing activity in the lavage fluids was significantly correlated with 2 indices of the severity of the clinical illness in patients with ARDS, the APACHE score, and the chest radiograph score. The correlation was diminished or ablated by removing the peptide with the monoclonal antibody bound to staphylococcal Sepharose 4B. This peptide accounted for 62.08% (SD = 15.88%) of the enzyme-releasing activity in fluids from lungs of patients with ARDS and 86.39% (SD = 24.46%) of the activity in fluids from lungs of normal control subjects. Therefore, ERP is the major neutrophil enzyme-releasing agent in the bronchoalveolar lavage fluid from patients with ARDS and from normal persons. There was a significant correlation between the neutrophil enzyme-releasing activity and the ERP concentrations in BAL of patients with ARDS. These observations suggest that modulation of neutrophil function by ERP significantly controls the protease and peroxidase loads in the lungs of patients with ARDS.