Method: Recombinant human PSP was produced in E. coli and CHO cells and purified by affinity chromatography. Minimal inhibitory concentration and bactericidal activity were determined by standard assays. Bpifa2 heterozygous mice (Bpifa2tm1(KOMP)Vlcg) were generated by lacZ replacement by the trans-NIH Knock-Out-Mouse Project and obtained from the KOMP-Repository. The heterozygous mice were mated to produce Bpifa2-/- homozygous offspring. Animal work was approved by IACUC, University of Minnesota. Saliva was collected from anesthetized mice by pilocarpine stimulation. LacZ staining was performed on frozen tissues, amylase was quantitated by Phadebas assay, PSP was identified by immunoblotting, H&E stain determined glandular lymphocyte infiltration.
Result: Genotyping of 250 mouse pups, revealed Mendelian distribution. Knockout-mice appeared healthy with normal grooming. Knockout saliva was less hydrophobic than wild-type saliva but knockout-mice were not susceptible to high temperatures suggesting that PSP was not necessary for grooming or temperature regulation. Knockout-mice stained positive for LacZ in submandibular and parotid glands, no lacZ was detected in other major organs. Salivary protein distribution was largely normal with increased levels of amylase. Stimulated saliva volumes did not differ in knockout and wild-type mice. Knockout salivary glands exhibited increased lymphocyte infiltration. Recombinant PSP did not exhibit bacteriostatic or bactericidal activity.
Conclusion: Current evidence does not support the previously proposed surfactant or antibacterial roles for PSP. Lymphocytic infiltration of salivary glands and our previous finding that PSP binds lipopolysaccharide suggest that PSP may modulate inflammatory pathways.