Protein kinase D1 is essential for the proinflammatory response induced by hypersensitivity pneumonitis-causing thermophilic actinomycetes Saccharopolyspora rectivirgula.

Hypersensitivity pneumonitis is an interstitial lung disease that results from repeated pulmonary exposure to various organic Ags, including Saccharopolyspora rectivirgula, the causative agent of farmer's lung disease. Although the contributions of proinflammatory mediators to the disease pathogenesis are relatively well documented, the mechanism(s) involved in the initiation of proinflammatory responses against the causative microorganisms and the contribution of signaling molecules involved in the host immune defense have not been fully elucidated. In the current study, we found that S. rectivirgula induces the activation of protein kinase D (PKD)1 in lung cells in vitro and in vivo. Activation of PKD1 by S. rectivirgula was dependent on MyD88. Inhibition of PKD by pharmacological PKD inhibitor Gö6976 and silencing of PKD1 expression by small interfering RNA revealed that PKD1 is indispensable for S. rectivirgula-mediated activation of MAPKs and NF-kappaB and the expression of various proinflammatory cytokines and chemokines. In addition, compared with controls, mice pretreated with Gö6976 showed significantly suppressed alveolitis and neutrophil influx in bronchial alveolar lavage fluid and interstitial lung tissue, as well as substantially decreased myeloperoxidase activity in the lung after pulmonary exposure to S. rectivirgula. These results demonstrate that PKD1 is essential for S. rectivirgula-mediated proinflammatory immune responses and neutrophil influx in the lung. Our findings also imply the possibility that PKD1 is one of the critical factors that play a regulatory role in the development of hypersensitivity pneumonitis caused by microbial Ags and that inhibition of PKD1 activation could be an effective way to control microbial Ag-induced hypersensitivity pneumonitis.

Isolation and possible relevance of Thermoactinomyces candidus proteinases in farmer's lung disease.

The thermophilic actinomycetes are the most common etiological agents causing hypersensitivity pneumonitis. Antigen preparations of these organisms contain proteolytic activity. Further investigation of the proteinases of the thermophilic actinomycetes was undertaken to determine whether this activity may contribute directly to the pathogenesis of hypersensitivity pneumonitis and pulmonary mycotoxicosis. The presence of proteolytic activity in aerosolized dust from moldy silage was demonstrated, and antibodies to two proteolytic enzymes from Thermoactinomyces candidus were found in the blood of farmer's lung patients who had been sensitized to this organism. These two enzymes were isolated from culture filtrate antigen preparations that had been partially characterized with respect to the proteolytic activities and their interaction with human serum proteinase inhibitors. Both proteinases belonged to the serine class of endopeptidases. Neither proteinase was inhibited by alpha 1-proteinase inhibitor or alpha 1-antichymotrypsin. Both proteinases were inhibited by alpha 2-macroglobulin. One of the proteinases had elastase activity. Inhalation of these proteinases apparently does occur, and they may induce an inflammatory response in the lungs since they are not inhibited by the main proteinase inhibitors protecting the lung.

Raised enzyme markers of chronic inflammation in asymptomatic farmers' lung.

Subclinical inflammatory activity may be one of the factors which influences the variable natural history of farmers' lung. Serum lysozyme (LYS) and angiotensin converting enzyme (ACE) have been measured in 52 farmers with a previous history of farmers' lung and in 51 healthy control farmers. The group with farmers' lung assessed during the winter, although having had no recent acute symptoms, had significantly higher levels of LYS and ACE compared to both healthy control farmers seen in winter and farmers' lung subjects seen in summer. There was a mild but significant negative correlation between LYS and farm size in the farmers' lung subjects assessed in winter. The results suggest that active inflammation may be present in subjects with farmers' lung in the absence of acute symptoms during the season when dust exposure occurs as the result of feeding cattle.

Angiotensin-converting enzyme in farmer's lung.

Serum levels of angiotensin-converting enzyme were measured in a group of patients with farmer's lung and a group of precipitin-positive subjects with no history of farmer's lung. The levels did not differ significantly from control subjects matched for age and smoking history. The mean serum level of angiotensin-converting enzyme in a group of acutely ill patients with farmer's lung was significantly reduced. An acute challenge of three patients with Micropolyspora faeni did not produce an increase in serum levels of angiotensin-converting enzyme. These studies suggest that an increased serum level of angiotensin-converting enzyme can be a diagnostic aid in making a differential diagnosis between sarcoidosis and farmer's lung.