Pulmonary macrophage growth factor

Pathogenesis of pulmonary fibrosis induced by chrysotile asbestos. Longitudinal light and electron microscopic studies on the rat model

A single instillation of 1 mg chrysotile B with a fiber length between 0.05 and 0.2 micron in 0.1 ml tricaprylin was made via a polyvinyl catheter into the lower lobe of the right lung of 120 six-week-old Wistar rats under anesthesia. The animals were killed at intervals between five minutes and two years. The lower lobes of the right lung were investigated by light and electron microscopy. The process of pulmonary fibrosis induced by asbestos can be subdivided into four phases: these are the phase of phagocytosis (five to 15 min), the phase of granuloma formation (between one and two weeks), the phase of septal fibrosis (between two and six months) and finally the scar stage (after one year). After instillation of small asbestos fibers into the alveoli, a major proportion of these fibers is phagocytosed by alveolar macrophages after five minutes and leaves the lungs via the airways. A proportion of the fibers penetrates through the alveolar wall (mostly conveyed by type I pneumocytes) and reaches the interstitium of the lungs. There, the fibers are taken up by pulmonary tissue macrophages and giant cells. Within the phagolysosomes, the fibers are broken down into fragments less than 0.01 micron in length. Type II pneumocytes produce surfactant in excess. These cells become necrotic, tubular myelin and lamellar bodies pass into the alveoli and into the interstitium. Surfactant is phagocytosed by resident macrophages. These macrophages can break down. Besides asbestos and surfactant, mediators of fibrillogenesis are released. Macrophages following up from blood monocytes ingest surfactant and asbestos. This process is perpetuated up to complete scarring. After two years, small asbestos fibers less than 0.01 micron long are present in fibroblasts and pleural mesothelia.

Role of polypeptide growth factors in normal and abnormal growth

In the preceding sections we have shown evidence that growth-promoting factors are involved in three basic situations. In normal embryonic development and function of mature organisms, growth factors such as NGF and EGF are of prime importance in supporting the necessary embryonic cell proliferation and the development of specific cell types. Other factors operate on subsets of mature cells during specialized functions such as inflammation. Included in this set would be factors such as CSF/MGF and Interleukin-2. Another basic function of growth factors has been shown to be wound repair and organ regeneration. This includes the well characterized PDGF and FGF as well as the various renotropic factors and liver growth factors. As these factors must operate in mature organisms with many different cell types and similar cell types in many locations, more specificity is needed than in embryonic growth. This has resulted in the organ specific factors such as the renotropins and in the unique delivery system of the PDGF. The recent discovery and characterization of the transforming growth factors has provided a possible connection between embryonic and normal developmental growth and the rapid cellular proliferation characteristic of tumor cells. The TGF not only interacts with receptors for normal growth factors such as EGF but are also detectable in low levels in normal tissue and embryos. The exact relationships between these various factors will have to await the determinations of more amino acid sequences for comparisons. The other tumor-related product, tumor angiogenesis factor, is also found in normal tissue and inflammatory reaction sites.(ABSTRACT TRUNCATED AT 250 WORDS)