Expression of Receptors for C5a Anaphylatoxin (CD88) on Human Bronchial Epithelial Cells: Enhancement of C5a-Mediated Release of IL-8 upon Exposure to Cigarette Smoke

Abstract

Results are presented that demonstrate a heightened responsiveness of human bronchial epithelial cells (HBECs) toward the complement-derived anaphylatoxin C5a when these cells are exposed to cigarette smoke. This C5a response is possible because we show at both the protein and mRNA levels that HBECs constitutively express receptors for C5a (C5aR, CD88). Control (untreated) HBECs responded to C5a (50 nM) by releasing the proinflammatory cytokine IL-8 at low but significant levels. However, exposure of HBECs to 5% cigarette smoke extract (CSE) for at least 15 min resulted in an increase in the ability of an anti-human C5aR Ab to bind to the cell surface. CSE-treated HBECs responded in a dose-dependent fashion to human recombinant C5a and to a conformationally biased decapeptide agonist of C5a (YSFKPMPLaR) by releasing IL-8. The levels of IL-8 released in response to C5a were significantly greater in CSE-treated HBECs than in control HBECs. Moreover, this C5a-mediated release of IL-8 from CSE-treated HBECs was significantly reduced in the presence of the anti-human C5aR Ab. These results indicate that HBECs constitutively express C5aRs and that exposure to environmental irritants such as cigarette smoke modulates the expression and responsiveness of these C5aRs toward the C5a-mediated release of IL-8.

Protein Kinase C-α Mediates Cigarette Smoke Extract- and Complement Factor 5a-Stimulated Interleukin-8 Release in Human Bronchial Epithelial Cells

“…7 In addition, we have shown that receptors for complement factor 5a (C5a) are constitutively present on the surface of HBEC and that CSE exposure initiates an increase in the population of C5a receptor-positive cells. 8 We have also shown that IL-8 release in response to CSE is increased significantly if HBEC are subsequently treated with C5a. 8 It seems that exposure of HBEC to CSE enhances the responsiveness of the C5a receptor on these cells to C5a-mediated release of IL-8.…”

“…8 We have also shown that IL-8 release in response to CSE is increased significantly if HBEC are subsequently treated with C5a. 8 It seems that exposure of HBEC to CSE enhances the responsiveness of the C5a receptor on these cells to C5a-mediated release of IL-8. In addition, we demonstrated that CSE activates protein kinase C (PKC) and that PKC activation is required for CSE-enhanced C5a-mediated release of IL-8 in HBEC.…”

“…We have found that HBEC release significantly more IL-8 than untreated cells when stimulated with CSE and C5a. 7,8 We have also reported that receptors for C5a are constitutively present on the surface of HBEC and that CSE exposure initiates an increase in the population of C5a receptor-positive cells. 8 We wanted to examine the role of C5a receptors in the release of IL-8 in HBEC.…”

“…7,8 We have also reported that receptors for C5a are constitutively present on the surface of HBEC and that CSE exposure initiates an increase in the population of C5a receptor-positive cells. 8 We wanted to examine the role of C5a receptors in the release of IL-8 in HBEC. HBEC were treated either with CSE (5%) for 1 hour followed by C5a (50 nM) for 17 hours or C5a receptor antagonist peptide (N MePhe-Lys-Pro-dCha-Trp-dArg) 13 (0.1 M) for 1 hour followed by CSE for 1 hour followed by C5a for 17 hours.…”

“…CSE was used at 5% concentration, as this concentration has been found to be the least toxic dosage producing maximal PKC activity in the HBEC. 8,12 PMA, LY36196, and Gö 6976 were dissolved in dimethyl sulfoxide. This vehicle was determined to have no biologic activity in the assays used.…”