Characterization of the ovine ortholog of secretory leukoprotease inhibitor

There is great interest in the use of the sheep as a model for the investigation of inflammation in the lung. The serine antiproteases secretory leukoprotease inhibitor (SLPI) and elafin are important "alarm antiproteases" in the lung and have potentially important roles in the innate immune response. SLPI was first characterized in man and subsequently in murine, porcine, and rat tissues. Here we present the first data concerning the gene and cDNA sequence encoding for the ovine ortholog of SLPI, a protein of 132 amino acids with 66% sequence identity at the amino acid level with human SLPI. A 24-amino-acid signal sequence signifies that, like the other mammalian orthologs, ovine SLPI is a secreted protein. Tissue distribution of expression is demonstrated by reverse transcription polymerase chain reaction (RT-PCR) and shows features similar to SLPI expression in other mammals, specifically at mucosal surfaces such as the upper respiratory and intestinal tracts, and also the skin, liver, and kidney. This distribution lends credence to SLPI having important roles in innate immunity. We have also cloned the ovine SLPI cDNA into an expression vector and expressed the ovine SLPI protein in vitro. This has enabled us to demonstrate that ovine SLPI is correctly processed (Western blot analysis and SELDI-TOF mass spectrometry analysis) and has biological antihuman neutrophil elastase activity. In summary, the ovine ortholog of SLPI shows similarities to other members of the SLPI family and has all the features of a modulator of innate immunity.