Cigarette smoke is the leading risk factor for the development of chronic obstructive pulmonary disease (COPD). Accumulation of neutrophils but not eosinophils is a characteristic feature of the inflammatory response associated with COPD (Jeffery, 1998). We have recently shown that CSE synergises with IL-1ß in the induction of IL-8 from THP-1 monocytes (Walters, 2003). Human airway smooth muscle cells (HASMC) are a rich source of neutrophil as well as eosinophil specific chemokines when stimulated with inflammatory cytokines such as IL-1ß and TNF(Chung, 2000). However, the effect of CSE on chemokine release from HASMC has not yet been investigated.

HASMC were cultured from dissected bronchi removed after surgery using collagenase digestion. Cigarette smoke solution was prepared as previously described (Walters, 2003) and diluted to the required strength with DMEM. Confluent cells were exposed to CSE in the presence and absence of TNFa or IL-1ß (1 ng ml^-1) at 37ºC. After 24 hrs, supernatants were collected and assayed for IL-8 and eotaxin by ELISA. All data (n=3) were obtained from one donor and are representative of two other donors. Data are expressed as mean SEM and were analysed with Students t-test.

CSE induced a bell shape response for IL-8 release from HASMC with maximum induction of IL-8 at a concentration of 10% CSE (baseline 22.2 ± 4.8; 10% CSE 150.3 ± 23.8 pg ml^-1; figure 1A). TNF and IL-1ß alone induced the release of IL-8 from HASMC (TNF: 456.3 ± 32.3; IL-1ß: 1796.5 ± 236.7 pg ml^-1; figure 1B). In combination with 5 % CSE, no effect was seen with IL-1ß on the induction of IL-8 release from HASMC (IL-1ß + 5 % CSE: 2287.4 ± 113.2 pg ml^-1). Synergy was observed when cells were stimulated with 7.5 % CSE and TNF (TNF + 7.5% CSE 973.2 ± 21.4 pg ml^-1, p<0.001).

Figure 1: Effect of CSE, TNF and IL-1ß on IL-8 and eotaxin production by HASMC.

By contrast, CSE did not induce eotaxin production from HASMC (figure 1A). In fact, TNF- or IL-1ß- induced eotaxin release (figure 1B) was completely inhibited in the presence of 7.5% CSE.The results demonstrate that CSE stimulates the release of the neutrophil chemotactic cytokine IL-8 but inhibits the production of the eosinophil chemotactic factor eotaxin stimulated by TNF and IL-1ß in HASMC. Considering the anatomical location of HASMC with proximity to the vasculature, these data suggest that HASMC play an important role in promoting neutrophil migration from the vasculature to the interstitium in lung diseases associated with cigarette smoke and may help to explain why COPD unlike asthma, is not associated with eosinophil recruitment.

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