Cleaved SLPI as a marker for exacerbation in cystic fibrosis

Abstract

Chronic infection in CF leads to an increased inflammatory response and disruption of the lung's antiprotease screen. One antiprotease affected is Secretory Leucocyte Protease Inhibitor (SLPI). The role of SLPI is to protect tissues from the detrimental effects of proteases such has neutrophil elastase (NE). In CF patients, chronically infected with P. aeruginosa, SLPI is cleaved due to excess levels of NE. NE cleavage of SLPI results in the generation of a C-terminal polypeptide fragment, cleaved SLPI (C-SLPI). We predict C-SLPI to be a novel biomarker for the detection of exacerbation in CF patients. An amino acid sequence within C-SLPI was used has an immunogen to generate hybridomas expressing monoclonal antibodies to C-SLPI. In silico modelling of the predicted C-SLPI epitope was performed. Monoclonal antibodies purified from the supernatants of these hybridomas were assayed via ELISA for activity against both C-SLPI and full-length native SLPI. Additionally, CF patient sputum samples were assayed for C-SLPI. In silico modelling showed the epitope to be exposed on C-SLPI but not on full-length native SLPI. An ELISA for recombinant C-SLPI demonstrated that these antibodies are able to detect C-SLPI ranging in concentration from 2000 ng/ml to 2.7 ng/ml; cross reactivity with full-length SLPI was less than 0.5% indicating high specificity for C-SLPI. Critically, we showed the monoclonal antibodies are able to detect C-SLPI in sputum samples from CF patients and observed significant differences in C-SLPI between stable and exacerbating CF patients. Successful detection of both recombinant and native C-SLPI by these antibodies we are pursuing further testing with a broader range of CF and COPD patient samples.