SERUM SECRETORY LEUKOPROTEASE INHIBITOR (SLPI) CONCENTRATION DOES NOT ALTER DURING EXACERBATIONS OF CHRONIC BRONCHITIS (CB) DESPITE CHANGES IN SOL SLPI CONCENTRATION

Sullivan, A.L., Bayley, D.L., O'Brien, C., Gompertz, S., Stockley, R.A.

Lung Investigation Unit, Queen Elizabeth Hospital, Birmingham B15 2TH

During exacerbations of CB, sputum SLPI falls for unknown reasons. Animal studies show intratracheally-administered SLPI moves rapidly into the circulation, and serum SLPI rises in conditions such as pneumonia with increased capillary leakage. We hypothesised that sol SLPI falls during exacerbations of CB because of greater diffusion of SLPI into the circulation.

We tested this hypothesis by examining serum and sputum from patients with CB during exacerbations and in the stable state. SLPI, neutrophil elastase (NE) activity, myeloperoxidase (MPO), albumin and alpha-1 antitrypsin (a1AT) were measured. Serum SLPI concentration did not vary significantly from exacerbation to stable state (median 4.04nM and 3.69nM respectively, p=0.075 (Kruskal-Wallis)), although the sol SLPI fell at exacerbation (median 1.89μM and 3.317μM respectively, p<0.005). Serum SLPI concentration did not correlate with sol SLPI, inflammation (sol NE or MPO), or plasma leak (sol:serum albumin or a1AT ratio).

We conclude that the fall in sol SLPI during exacerbations of CB is not a result of increased loss of SLPI into the circulation. We speculate that because serum SLPI does not relate directly to sol SLPI , it may not originate from the lungs, or if it does, by a more complex route than simple diffusion into the circulation.

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