The arrival of inflammatory phagocytic cells, namely neutrophils and mononuclear phagocytes, in the pleural space is a hallmark of pleural inflammation. It is probable that the temporal arrival of cells is mediated via the release of chemotactic cytokines by activated mesothelial cells. We hypothesized that human pleural mesothelial cells activated by bacterial endotoxin lipopolysaccharide (LPS), interleukin-1 beta (IL-1 beta), or tumor necrosis factor-alpha (TNF-alpha) release cell-specific chemokines from the C-C and C-X-C family of chemokines, specifically monocyte chemoattractant protein 1 (MCP-1) and IL-8. We evaluated supernatants of stimulated mesothelial cells for biologic chemotactic activity for monocytes and neutrophils and quantitative antigenic protein levels for MCP-1 and IL-8. Expression of the proteins at mRNA level was tested via Northern blot analysis. We found that responses to LPS were significantly higher (P less than 0.05) than control supernatants of unstimulated mesothelial cells. Responses to IL-1 beta and TNF-alpha were significantly greater than those to LPS. Neutralization studies with specific rabbit anti-MCP-1 and IL-1 antibody demonstrated significant decreases in bioactivity for MCP-1 and IL-8, indicating that mesothelial cell-derived MCP-1 and IL-8 play a significant role in the chemotactic activity seen in stimulated mesothelial cell supernatants. On specific enzyme-linked immunosorbent assay testing, stimulated mesothelial cells produced significantly more MCP-1 and IL-8 when stimulated with IL-1 beta or TNF-alpha as compared to LPS. mRNA expression for MCP-1 peaked within 2 to 4 h following stimulation and was noted as early as 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrapleural instillation of tetracycline hydrochloride (TCN) is an effective means of achieving pleural fibrosis. However, its mechanism of action remains unknown. To evaluate the hypothesis that TCN stimulates pleural mesothelial cells to release growth-factor-like activity for fibroblasts we performed the following experiments. Rat visceral pleural mesothelial cells were incubated with TCN at doses ranging from 0.01 microgram/ml to 100 mg/ml. The conditioned media (CM) were collected after incubation for 2 to 48 h. CM caused fibroblasts to increase incorporation of thymidine when compared with CM that was unexposed to TCN (p less than 0.05). This growth-factor-like activity continued to be produced by mesothelial cells for 48 h after removal of TCN from the medium. There was a dose-response relationship since increasing doses of TCN to as much as 1 mg/ml caused increasing production of growth-factor-like activity without mesothelial cell injury as measured by trypan blue exclusion. The growth factor activity was a competence-type activity. It coeluted with human PDGF at a molecular weight of 31,000. It was heat-stable (100 degrees C for 10 min) and sensitive to trypsin and papain but not to heat-inactivated trypsin. Addition of cycloheximide or actinomycin D inhibited its production. TCN did not have any direct effect on fibroblasts. Bleomycin CM did not contain growth-factor-like activity for fibroblasts. These data demonstrate that TCN stimulates mesothelial cells to release a growth-factor-like activity for fibroblasts. This phenomenon may play an important role in TCN-induced pleural fibrosis.

Alcohol consumption is known to predispose the host to more frequent and severe bacterial infections, suggesting that alcohol compromises the normal immune function of the lung. The pulmonary alveolar macrophage is the resident host defense cell in the lung and forms the first line of defense against invading microorganisms. One of the mechanisms whereby alveolar macrophages kill bacteria is by releasing toxic oxygen radical species, such as superoxide anion and hydrogen peroxide. We hypothesized that chronic alcohol consumption caused alveolar macrophage dysfunction leading to inhibition of oxidant production when stimulated. Our data demonstrate that alveolar macrophages harvested from alcohol-treated rats release significantly lower quantity (p < 0.05) of both superoxide anion and hydrogen peroxide when stimulated with several different types of stimuli including heat-killed Staphylococcus aureus, soluble immune complexes or phorbol myristate acetate. Pair-fed control rats who received isocaloric quantities of maltose dextrin in their diet to compensate for the alcohol were able to produce oxidants in equal quantities when stimulated, to rats who were fed a normal diet. Similar results were noted in vitro experiments when alveolar macrophages harvested from normal rats were incubated in vitro in alcohol-containing media and then stimulated with the aforementioned stimuli. Alveolar macrophages, which had been incubated in alcohol for 4 hr, showed significant decreases in their ability to produce superoxide anion. This defect was noticeable for a period up to 8 hr following removal of alveolar macrophages from the alcohol-containing media.(ABSTRACT TRUNCATED AT 250 WORDS)

Injury to the pleura ultimately results in either repair with fibrosis or repair without fibrosis and a reestablishment of the normal mesothelial monolayer. The role of the mesothelial cell, and of local mediators, in these repair processes remains essentially undefined. In order for repair without fibrosis to occur, mesothelial cells, in response to local mediators, must be capable of migration and/or proliferation to cover the injured and denuded mesothelium. We hypothesized that rat pleural mesothelial cells were capable of both chemotaxis and proliferation in response to thrombin. In an in vitro assay, mesothelial cells demonstrated directed migration in response to a known chemoattractant, formylmethionylleucylphenylalanine. In addition, mesothelial cells demonstrated chemotaxis in a dose-dependent manner in response to thrombin, with a maximal response at a concentration of 10(-8) M. Finally, this chemotaxis was blocked by a specific blocker of thrombin, antithrombin 3. Thrombin also stimulated mesothelial cell proliferation, which was measured both in a [3H]thymidine incorporation assay and by direct cell counts. Again, the response was dose dependent, with the maximal response at 10(-8) M causing the same amount of [3H]thymidine incorporation as 10% fetal bovine serum. As before, this response was completely blocked by antithrombin 3. These results demonstrate that mesothelial cells are capable of both chemotaxis and proliferation in response to thrombin. Thrombin may play an important role in the regulation of pleural repair without fibrosis and the re-establishment of the mesothelial monolayer.

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