MURINE HYPERSENSITIVITY PNEUMONITIS - PRODUCTION AND IMPORTANCE OF COLONY-STIMULATING FACTORS IN THE COURSE OF A LUNG INFLAMMATORY REACTION

The release of colony-stimulating factors (CSFs) and their contribution to the inflammatory response in the lungs of mice exposed by the intranasal route to the actinomycete Faeni rectivirgula (150 mug/day, 3 days/wk), an important thermophilic actinomycete that determines farmer's lung in humans, was examined. Bronchoalveolar lavages (BAL) and lung homogenates of normal mice or saline-instilled mice contained undetectable levels (< 0.5 U/ml) of the cytokines interleukin-3 (IL-3), colony-stimulating factor-1 (CSF-1), and granulocyte/macrophage colony-stimulating factor (GM-CSF). Mice instilled with F. rectivirgula developed a CSF cytokine response early (24 h) after the instillation that increased and plateaued 2 wk later, and stayed high thereafter. Similarly, lung homogenates of F. rectivirgula-challenged mice contained significant levels of all three CSFs from 24 h after treatment until termination of the experiment. The offending agent itself, F. rectivirgula, was found to directly induce the secretion of IL-3 and GM-CSF from isolated mouse BAL cells and mouse splenocytes, at doses ranging from 1 to 100 mug/nil. This was not due to contaminating endotoxin, as inclusion of polymyxin B did not modify this release. Instillation of antibodies against the CSFs in mice challenged with F. rectivirgula did not modify the increase in BAL cell number determined by the challenge (11-fold increase in BAL cell number in F. rectivirgula-instilled mice at 3 wk, whether given anti-CSFs or not). Moreover, direct intratracheal infusion of CSFs (5,000 U of IL-3/CSF-1/GM-CSF) every week did not change the cellular response seen in challenged mice. In a last set of experiments, we demonstrated that BAL fluid from F. rectivirgula-challenged mice enhanced the release of the monokine tumor necrosis factor-alpha (TNF-alpha) from alveolar macrophages (AM) stimulated with F. rectivirgula. AM incubated with normal BAL fluid treated with 10 mug of F. rectivirgula released 36 +/- 8 U of TNF-alpha whereas AM treated with a 50% (vol/vol) BAL fluid from mice instilled intranasally with F. rectivirgula released 102 +/- 18 U of TNF-alpha upon stimulation (P < 0.001). This enhanced TNF-alpha release was partially abrogated by including a rabbit anti-GM-CSF antiserum, with a release of 62 +/- 9 U (P < 0.01 versus cells treated with a BAL fluid alone). Collectively, these findings suggest that (1) CSFs in the lung are elicited early after challenge with actinomycetes causing farmer's lung, (2) F. rectivirgula itself is a strong inducer of CSFs from splenocytes and BAL cells, (3) CSFs do not play a major role in cellular recruitment in hypersensitivity pneumonitis, at least in the early phase of the disease, and (4) a potential detrimental role for CSFs may be their ability to prime macrophages for subsequent release of proinflammatory cytokines such as TNF-alpha.