We are participating in a collaborative project at NIOSH on mechanisms of silicosis, in which rats were exposed to filtered air (control) or silica aerosol of 15 mg/m3 (6 hr/day, 5 days/week), with assays conducted at intervals over a 6 month period. We are especially interested in the role of nitric oxide (NO) in the pathophysiology of lung disease. One source of NO is the alveolar macrophage, known to express the inducible form of nitric oxide synthase (iNOS); we used immunohistochemical techniques to determine whether iNOS is upregulated in alveolar macrophages and other lung sources in response to silica.

Silica-exposed and air control animals were sacrificed after 10, 20, 41, 79, and 116 days of exposure. Formalin fixed, paraffin embedded tissues were cut at 5μm, deparaffinized in xylene and rehydrated. Slides were microwaved in citrate buffer, pH 6.0 for antigen retrieval.2 After blocking endogenous peroxidase in 3% H2O2:Methanol (1:1), slides were placed in 10% BSA for 30 min, then incubated overnight in the primary antibody (Monoclonal anti-iNOS, Transduction Laboratories, N32020, 1:50 dilution)