**8. Homocysteine and CRP: Evidence for immune activation?**

Serum C-reactive protein (CRP), is a ubiquitous marker of systemic inflammation, mortality and hospitalisation in COPD (Dahl et al, 2007; Man et al, 2004), cardiac disease in COPD (Sin et al, 2003) and of cardiac disease in the elderly (Zakai et al, 2007). High CRP levels have also been shown to correlate with low 6-min walk test scores (de Torres et al, 2007).

As shown in Table 1, both Seemungal et al and Fimognari et al measured serum CRP in their normal and COPD subjects and though their samples showed significantly different values for mean CRP, they both agreed that CRP was elevated in the COPD subjects compared to asymptomatic controls. The CRP levels in the normal controls in the Seemungal et al study was similar to that in previously published American and Dutch controls (Broekhuisen et al, 2005; Sin & Man 2003) and the greater value of CRP in COPD in the Seemungal et al study is the same as that attributed to COPD by Gan et al in their metaanalysis (Gan et al, 2004).

The Seemungal et al study found a correlation between CRP and HCY which was not found (rho= 0.377, p = 0.005) in the Fimognari et al study. The clinical implication of this finding from the Seemungal et al study is unclear at present more so because it was not supported by the Fimognari et al study. However, a similar correlation between HCY and CRP (as observed by Seemungal et al) has been reported in psoriatic arthritis (Sattar et al, 2007), in cancer (Schroecksnadel 2007) and in elderly patients with cardiovascular disease and dementia (Ravaglia et al, 2004). Taken together these results suggest that HCY may play a role in immune activation in some chronic diseases (Schroecksnadel et al, 2007) and its relationship to HCY in COPD may be a further indicator of the role of HCY in oxidative stress in COPD (Folchini et al, 2011).
