The bovine salivary proteins BSP30a and BSP30b are independently expressed BPI-like proteins with anti- Pseudomonas activity

The family of BPI-like proteins are thought to play a role in innate immunity of the airways and oral cavity. They have similarities with bactericidal/permeability-increasing protein (BPI), an important host defence molecule in mammals, in the nucleotide sequence of their mRNAs, organisation of exons and their predicted protein structure. We compared the expression and function of 2 of the 13 known bovine BPI-like proteins, BSP30a and b, which together constitute 30% of the total protein in bovine saliva. Despite their recent divergence, we found that the two proteins have unique expression patterns, considerable inter- and intra-animal variation in abundance and differ in their glycosylation status. Recombinant and native BSP30a and b exhibited growth suppression activity against Pseudomonas aeruginosa and Streptococcus pneumoniae. Native BSP30a and b had no significant lipopolysaccharide-binding activity. These data provide functional evidence supporting a role for the BPI-like proteins in host defence and suggest that BSP30a and b contribute to the growth suppression function of bovine saliva through a mechanism independent of LPS opsonisation.