Tissue Kallikrein in Human Plasma

Abstract

In order to analyze immunoreactive tissue kallikrein (TK) in human plasma, three kinds of enzyme-linked immunosorbent assay (ELISA) systems for human urinary kallikrein (HUK) were developed. All three types of TK in the plasma, i.e., active kallikrein, proka-Ilikrein and kallikrein-aiantitrypsin (α₁AT) complex could be measured by competitive ELISA (C-ELISA). However, sandwich ELISA (S-ELISA) showed more strict specificity. Namely, both active and prokallikreins were measured by S-ELISA, while kallikrein-aiAT complex was hardly measurable. In this ELISA system, kallikrein-α₁AT complex bound to anti-HUK antibody fixed on the solid phase. Horseradish peroxidase (HRP)-labeled anti-HUK Fab'(second antibody), however, hardly reacted with this antigen-antibody complex on the solid phase probably due to some steric hindrance. Measurement of this kallikrein-aiAT complex was made possible by using HRP-labeled anti-α₁AT IgG instead of HRP-labeled anti-HUK Fab' as the second antibody (HS-ELISA).
Using these ELISAs we analyzed TK in the plasma and the following observations were made. First, the greater part of TK in the plasma was found in a form of a complex with α₁AT.Second, the amount of free type TK was very small and the most part of this type TK in normal plasma was prokallikrein.