Effects of purified macrophage RNase on granuloma fibroblasts with reference to silicosis

Chronic exposure to glucocorticoids shapes gene expression and modulates innate and adaptive activation pathways in macrophages with distinct changes in leukocyte attraction

Glucocorticoids (GCs) have been used for more than 50 y as immunosuppressive drugs, yet their efficacy in macrophage-dominated disorders, such as chronic obstructive pulmonary disease, is debated. Little is known how long-term GC treatment affects macrophage responses in inflammatory conditions. In this study, we compared the transcriptome of human macrophages, matured in the presence or absence of fluticasone propionate (FP), and their ability to initiate or sustain classical activation, mimicked using acute LPS and chronic IFN-γ stimulation, respectively. We identified macrophage gene expression networks, modulated by FP long-term exposure, and specific patterns of IFN-γ- and LPS-induced genes that were resistant, inhibited, or exacerbated by FP. Results suggest that long-term treatment with GCs weakens adaptive immune signature components of IFN-γ and LPS gene profiles by downmodulating MHC class II and costimulatory molecules, but strengthens innate signature components by maintaining and increasing expression of chemokines involved in phagocyte attraction. In a mouse model of chronic obstructive pulmonary disease, GC treatment induced higher chemokine levels, and this correlated with enhanced recruitment of leukocytes. Thus, GCs do not generally suppress macrophage effector functions, but they cause a shift in the innate-adaptive balance of the immune response, with distinct changes in the chemokine-chemokine receptor network.

Minerals, fibrosis, and the lung

Determinants of pulmonary fibrosis induced by inhaled mineral dusts include quantity retained, particle size, and surface area, together with their physical form and the reactive surface groups presented to alveolar cells. The outstanding problem is to ascertain how these factors exert their deleterious effects. Both compact and fibrous minerals inflict membrane damage, for which chemical mechanisms still leave uncertainty. A major weakness of cytotoxicity studies, even when lipid peroxidation and reactive oxygen species are considered, lies in tacitly assuming that membrane damage suffices to account for fibrogenesis, whereas the parallel occurrence of such manifestations does not necessarily imply causation. The two-phase procedure established that particles, both compact and fibrous, induce release of a macrophage factor that provokes fibroblasts into collagen synthesis. The amino acid composition of the macrophage fibrogenic factor was characterized and its intracellular action explained. Fibrous particles introduce complexities respecting type, durability, and dimensions. Asbestotic fibrosis is believed to depend on long fibers, but scrutiny of the evidence from experimental and human sources reveals that a role for short fibers needs to be entertained. Using the two-phase system, short fibers proved fibrogenic. Other mechanisms, agonistic and antagonistic, may participate. Growth factors may affect the fibroblast population and collagen production, with cytokines such as interleukin-1 and tumor necrosis factor exerting control. Immune involvement is best regarded as an epiphenomenon. Downregulation of fibrogenesis may follow collagenase release from macrophages and fibroblasts, while augmented type II cell secretion of lipid can interfere with the macrophage-particle reaction.

Penetration of macrophage ribonuclease into fibroblasts and the effects on nucleic acid and collagen metabolism

RNAase isolated from macrophage culture medium was labelled with 3H-acetic anhydride. The acetylation density of 1.8 acetyl residues/10(4) dalton RNAase was achieved. After just 5 mins' incubation of granulation-tissue slices with 3H-Ac-RNAase, the enzyme had entered fibroblasts, and after 20 min there was only slight increase of the radioactivity. After 1 h incubation 32% of the ingested RNAse was in the nuclei, 23% in the cytosol and about 2% in RER. After the same period of incubation with 3H-Ac-RNAase, 47% of nuclear RNA of the fibroblasts was lost, as compared with the control incubation, and the amount of cytosol RNA increased by about 40%. During a 3-h incubation, in low concentrations, the biologically active macrophage RNAase stimulated. 3H-thymidine incorporation into DNA of proliferative granulation-tissue slices. Thus it was concluded that the fibrogenic effect of the macrophage RNAase on the granulation-tissue fibroblasts takes place through the RNA metabolism and the main target of the enzyme in the fibroblasts is the nuclear RNA.

Penetration of various mononuclear ribonucleases into rat experimental granulation-tissue fibroblasts and their intracellular effects

The penetration of five different mononuclear ribonucleases into the subcellular particles of rat experimental granulation-tissue fibroblasts was compared, along with the effects of the enzymes on the fibroblast RNA fractions. Ribonucleases from normal and silica-treated rat peritoneal macrophages have been shown before to regulate the nucleic acid and protein metabolism of rat experimental granulation-tissue fibroblasts. These biologically active enzymes were taken into the fibroblasts in a greater amount than the corresponding human monocyte enzymes and the biologically inactive rat macrophage ribonuclease. The biologically active macrophage enzymes were incorporated mainly into the nuclear fraction. The other three mononuclear ribonucleases were not found particularly in any subcellular compartment. Both biologically active macrophage enzymes degraded the nuclear RNA of fibroblasts and released it to the soluble fraction in contrast to the biologically inactive macrophage enzyme and ribonuclease from normal human monocytes. Instead the ribonuclease from normal human monocytes seemed to degrade RNA in the soluble fraction. There were no marked differences in the subcellular effects of ribonucleases from normal and silica-treated macrophages. However, the treatment of human monocytes with silica changed their ribonuclease so that it split the nuclear RNA of fibroblast and released it to the soluble fraction in the same way as the biologically active macrophage enzymes did.