Accumulating evidence suggests that the early pulmonary inflammation pathogenesis in cystic fibrosis (CF) may be associated with an abnormal increase in the production of pro-inflammatory cytokines in the CF lung, even in the absence of infectious stimuli. We have postulated that if baseline abnormalities in airway epithelial cell production of cytokines occur in CF, they should be manifested in the CF bronchial submucosal glands, which are known to express high levels of CFTR (cystic fibrosis transmembrane conductance regulator) protein, the gene product mutated in CF disease. Immunohistochemical analyses showed that CF bronchial submucosal glands in patients homozygous for the deltaF508 deletion expressed elevated levels of the endogenous chemokine interleukin (IL)-8 but not the pro-inflammatory cytokines IL-1beta and IL-6, compared with non-CF bronchial glands. Moreover, basal protein and mRNA expression of IL-8 were constitutively up-regulated in cultured deltaF508 homozygous CF human bronchial gland cells, in an unstimulated state, compared with non-CF bronchial gland cells. Furthermore, the exposure of CF and non-CF bronchial gland cells to an elevated extracellular Cl- concentration markedly increased the release of IL-8, which can be corrected in CF gland cells by reducing the extracellular Cl- concentration. We also found that, in contrast to non-CF gland cells, dexamethasone did not inhibit the release of IL-8 by cultured CF gland cells. The selective up-regulation of bronchial submucosal gland IL-8 could represent a primary event that initiates early airway submucosal inflammation in CF patients. These findings are relevant to the pathogenesis of CF and suggest a novel pathophysiological concept for the early and sustained airway inflammation in CF patients.

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The aims of this study were (a) to determine if rat alveolar type II (ATIl) cells and human pulmonary epithelial-derived cells (A549 cell line) could generate (b) to characterize the cytokine regulation of IL-6 gene and protein expression in these cells, and (c) to detect the in vivo expression of immunoreactive IL-6 by human ATH cells. Rat ATH cells in primary culture secreted bioactive IL-6 and immunostained with an anti-IL-6 antiserum. Spontaneous IL-6 secretion by rat ATH cells amounted to 5,690±770 pg/ml/106 cells (n = 12) and was fivefold higher than spontaneous rat alveolar macrophages IL-6 secretion (1,052±286 pg/ml/106 cells, n = 8, P = 0.001). Rat alveolar macrophage conditioned media (CM) increased IL-6 secretion by rat ATH cells through the effect of IL-1 and TNF. IL-6 gene expression and IL-6 secretion by A549 cells was induced by 1L-lfi, TNFa, and by human alveolar macrophages and THP1 cells CM. Induction was abolished when CM were preincubated with anti-IL-lfi and anti-TNFa antibody. The combination of IFNy and LPS induced the expression of IL-6 mRNA by A549 cells whereas LPS alone had no effect. Immunohistochemical staining evidenced the expression of immunoreactive 1L-6 by hyperplastic ATHI cells in fibrotic human lung, a condition in which alveolar macrophages are known to be activated. ATII cells in normal human lung did not express immunoreactive 1L-6.Our findings demonstrate that ATH cells may be an important source of 1L-6 in the alveolar space thereby participating to the regulation of the intra-alveolar immune response. (J. Clin. Invest. 1994. 94:731-740.)

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The interaction of LPS (endotoxin) with the CD14-TLR4 receptor complex modulates the host innate immune response. Several studies using partial structures of LPS have suggested that TLR4 determines the ligand specificity of this complex, and that CD14 indiscriminately serves to deliver the ligand to TLR4. This conclusion has been made despite observations that the response of TLR4+/+,CD14−/− macrophages to LPS is very weak. To determine whether CD14 itself plays a role in specific ligand recognition, the influences of various partial structures of LPS on induction of the proinflammatory cytokine, TNF, by CD14+/+ and CD14−/− macrophages were compared. These studies show that the ligand specificities of CD14+/+ and CD14−/− macrophages are very different. When CD14 is present, the receptor complex shows exquisite specificity for smooth LPS, the major form expressed by Gram-negative bacteria; however, as increasing amounts of carbohydrate are removed from smooth LPS, the sensitivity of CD14+/+ macrophages decreases as much as 500-fold. In contrast, CD14−/− macrophages are unable to distinguish between smooth LPS and its various partial structures. Furthermore, CD14−/− macrophages are 150,000-fold less sensitive than CD14+/+ macrophages to smooth LPS. A similar ability to distinguish the differing LPS structures of various bacteria such as Bacteroides fragilis and Salmonella abortus are observed for CD14+/+, but not CD14−/−, macrophages. Thus, CD14+/+, but not CD14−/−, macrophages are highly sensitive to stimulation by natural forms of LPS and show the ability to distinguish between various LPS ligands, consistent with CD14 being a highly specific receptor.

According to the widely accepted view, neutrophil elastase (NE), a neutrophil-specific serine protease, is a major contributor to Pseudomonas aeruginosa infection-associated host tissue inflammation and damage, which in severe cases can lead to death. Herein, we provide for the first time compelling evidence that the host rather employs NE to protect itself against P. aeruginosa infection. Using a clinically relevant model of pneumonia, targeted deficiency in NE increased the susceptibility of mice to P. aeruginosa. We found that NE was required for maximal intracellular killing of P. aeruginosa by neutrophils. In investigating the mechanism of NE-mediated killing of P. aeruginosa, we found that NE degraded the major outer membrane protein F, a protein with important functions, including porin activity, maintenance of structural integrity, and sensing of host immune system activation. Consistent with this, the use of an isogenic mutant deficient in outer membrane protein F negated the role of NE in host defense against P. aeruginosa infection.