Regulation of human alveolar macrophage inflammatory cytokine production by interleukin-10.

Alveolar macrophages are the primary source of inflammatory cytokine production in the lung. Both site-specific and differentiation-specific factors play a role in cytokine production, and regulation of this activity in alveolar macrophages is distinctly different from that of circulating blood monocytes. Interleukin-10 (IL-10) inhibits the production of inflammatory cytokines [tumor necrosis factor (TNF)-alpha, interleukin-1 (IL-1), interleukin-6 (IL-6), and interleukin-8 (IL-8)] and enhances production of interleukin-1-receptor antagonist (IL-1ra) from endotoxin-stimulated human monocytes, but the effect of IL-10 on such activity in alveolar macrophages is unknown. This study was undertaken to determine the effect of recombinant IL-10 on endotoxin-stimulated cytokine production by human alveolar macrophages. TNF, IL-1, IL-6, and IL-8 secretions were significantly (P < 0.05) stimulated by endotoxin [lipopolysaccharide (LPS)] and were all significantly (P < 0.05) inhibited (median inhibition = 43%) by IL-10 (10 ng/ml). In contrast, IL-1ra was not stimulated by LPS and basal levels were not affected by IL-10. LPS also did not significantly elevate alveolar macrophage IL-10 secretion (< 100 pg/ml) and basal levels were undetectable (< 15 pg/ml). This potent inhibitory activity of IL-10 on inflammatory cytokine production by human alveolar macrophages suggests that exogenous IL-10 may be useful in treatment of inflammatory lung diseases such as adult respiratory distress syndrome.

Surfactant suppresses NF-kappa B activation in human monocytic cells.

In addition to biophysical properties, pulmonary surfactant has immunomodulatory activity. We previously demonstrated that both synthetic (Exosurf) and modified natural surfactant (Survanta) downregulated endotoxin-stimulated inflammatory c ytokine mRNA levels and protein products (tumor necrosis factor-alpha [TNF], interleukin-1-beta [IL-1], interleukin-6 [IL-6]) in human alveolar macrophages. In this study, we report that both Exosurf and Survanta suppress TNF mRNA and secretion (85 +/- 4% mean percent inhibition +/- SEM by Exosurf; 71 +/- 6% by Survanta) by endotoxin-stimulated THP-1, a human monocytic cell line. Because surfactant downregulated inflammatory cytokine production similarly in both normal human alveolar macrophages and the THP-1 cell line, we used this cell line to investigate whether surfactant affected transcriptional mechanisms. Specifically, we examined nuclear factor-kappa B (NF-kappa B) activation because it is crucial in transcriptional regulation of many inflammatory cytokine genes including TNF, IL-1, and IL-6. Electrophoretic mobility shift assays showed that both surfactants decreased activation of NF-kappa B. The presence of both p65 and p50 NF-kappa B components in LPS-activated THP-1 cells was confirmed by specific antibody induction of supershifts in mobility assays. These results are the first to suggest that surfactant's suppressive effects on inflammatory cytokine production may involve transcriptional regulation through inhibition of NF-kappa B activation.

Surfactant downregulates synthesis of DNA and inflammatory mediators in normal human lung fibroblasts.

The initial inflammatory event in the adult respiratory distress syndrome (ARDS) is followed by fibroproliferation and a cascade of fibroblast-derived mediators. Because lung fibroblasts may be exposed to surfactant as well as inflammatory cytokines during ARDS, we hypothesized that surfactant might modulate fibroblast activity. We previously demonstrated that surfactant inhibited production of inflammatory cytokines from endotoxin-stimulated human alveolar macrophages. In the current study the effects of surfactant on normal human lung fibroblast proliferative capacity and mediator production were examined. Both synthetic (Exosurf) and natural (Survanta) surfactant inhibited fibroblast [3H]thymidine incorporation. Examination of pre-S-phase events indicated stimulation of the immediate response gene, c-fos, and no effect on the G1/S cyclin, cyclin D1, suggesting that the surfactant block occurred elsewhere before S phase. The antioxidant N-acetyl-L-cysteine (NAC), like surfactant, inhibited [3H]thymidine incorporation. Furthermore, menadione, a generator of intracellular H2O2, stimulated fibroblast [3H]thymidine incorporation, and this was inhibited by surfactant. Interleukin-1 (IL-1)-stimulated secretion of the inflammatory mediators, IL-6 and prostaglandin E2, was also inhibited by surfactant. These data suggest that surfactant may modify lung fibroblast participation in ARDS sequelae by downregulating DNA synthesis and secondary inflammatory mediator production.

Regulation of human alveolar macrophage inflammatory cytokines by tyloxapol: a component of the synthetic surfactant Exosurf.

We previously demonstrated that the synthetic surfactant Exosurf and a modified natural surfactant, Survanta, both down-regulated endotoxin-stimulated production of inflammatory cytokines (tumor necrosis factor-alpha, interleukin-1 beta, interleukin-6) in human alveolar macrophages. To further characterize the source of the inhibitory effect of surfactant, the three individual components of Exosurf were evaluated. Dipalmitoylphosphatidylcholine had no effect on endotoxin-stimulated cytokine secretion. Cetyl alcohol (spreading agent) compromised macrophage function as measured by adherence. However, at concentrations equivalent to those found in the complete surfactant (Exosurf) preparation, tyloxapol (nonionic dispersing agent) was inhibitory in a dose-dependent manner. The viability of alveolar macrophages as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide cleavage assay was not affected by incubation in Exosurf or any of its individual components. Cytokine secretion and mRNA levels of endotoxin-stimulated alveolar macrophages were decreased by tyloxapol. These data suggest that tyloxapol alone, like Exosurf, has an inhibitory effect on cytokine production which may be pretranslationally mediated.