The purpose of this project is to understand the mechanisms of chronic interstitial lung disease by focusing on the interactions of two cytokines, interleukin-1 (IL-1) and tumor necrosis factor (TNF-alpha), with key cell types in a mouse model of fibrosis induced by silica. Reports from us and others demonstrate that IL-1 and TNF-alpha are important in pulmonary fibrosis induced by silica, but their means of action remain unknown. Our new findings support these concepts: increased macrophage production of TNF-alpha and IL-1 in evolving silicosis follow different time courses, and mice genetically deficient in TNF-alpha develop less inflammation and fibrosis after silica exposure than a cytokine-sufficient strain. This research will test the HYPOTHESES that IL-1 and TNF-alpha play critical roles in pulmonary fibrosis through localized effects which (a) perpetuate macrophage activation, (b) promote silicotic lesion formation, (c) stimulate T- lymphocyte proliferation and activation, and (d) cause fibroblasts to replicate. We PROPOSE that these mechanisms are somewhat redundant, and deletion of a single mediator will not prevent fibrosis entirely, but will modify its features and intensity. We shall test these concepts through 3 SPECIFIC AIMS: (1) To define the timing, activity, and localization of gene expression and secretion of pro-inflammatory cytokines (IL-1, TNF-alpha) by pulmonary macrophages following silica exposure of mice, (2) to modulate the immune-inflammatory and/or fibrotic response to silica by interventions which will improve understanding of pathogenetic mechanisms, and (3) To understand the geography of macrophage and lymphocyte location and cytokine expression within the evolving lesion produced by silica or by individual cytokines. We will use mice exposed to a silica aerosol shown to produce interstitial fibrosis, and will compare responses with inert titanium dioxide exposure. We will assess histology, lavage inflammatory cells, and total lung collagen as the outcome of exposures and interventions. We will assess cytokine production by macrophages as bioactivity, protein, and mRNA expression. We will localize the cells responsible for cytokine production in lavage and in tissue by in situ hybridization of mRNA. We will infer function to lymphocytes in lesions from phenotypes detected by immunocytochemistry. We will quantitate tissue responses by image analysis. We will use inbred mouse strains deficient in TNF-alpha, Il-1, or T-cells and new soluble IL-1 and TNF receptors to interdict specific pathways. The novel observations from this work will improve understanding o how activated macrophages recruit and stimulate lymphocytes, how macrophages and lymphocytes amplify pro-inflammatory signals in response to a known inducing agent (silica), and the degree to which deletion of defined communication pathways between cells can interdict the process of pulmonary fibrosis.
