Human kallikrein 8: Immunoassay development and identification in tissue extracts and biological fluids

Background: The serine protease human kallikrein 8 (hK8; neuropsin), a new member of the human kallikrein family, was predicted to be secreted; thus, it is expected to be present in biological fluids. The aim of this study was to develop a sensitive and specific immunoassay for hK8 (hK8-ELISA) and establish the distribution of hK8 in tissue extracts and biological fluids. Methods: Recombinant hK8 was produced in a baculovirus expression system and purified with a three-step chromatographic procedure. Purified hK8 was injected into mice and rabbits for antibody generation. A highly specific and sensitive sandwich-type immunoassay (ELISA) was developed using the rabbit and mouse antisera to hK8. The hK8-ELISA was then used to study the distribution of hK8 in various biological fluids and tissue extracts. Results: The dynamic range of the hK8-ELISA was 0.2 (detection limit) to 20 mug/L, and imprecision (CV) was <10% within this range. This hK8-ELISA was specific for hK8 and had no detectable cross-reactivity with other members of the human kallikrein family. With this assay, hK8 was detected in tissue extracts of esophagus (highest concentrations), skin, testis, tonsil, kidney, breast, and salivary gland and in the biological fluids breast milk (highest concentrations), amniotic fluid, seminal plasma, and serum. Furthermore, in some cancer cell lines, the concentration of hK8 was regulated by steroid hormones. Conclusions: We report for the first time production of recombinant hK8 protein, generation of antibodies, and development of a highly sensitive and specific immunoassay for quantification of hK8 in tissue extracts and biological fluids. This assay can be used to explore the potential of hK8 as a marker of cancer or other conditions. (C) 2003 American Association for Clinical Chemistry.