A solid phase enzyme linked immunofiltration assay for secretory leucocyte proteinase inhibitor.

A solid phase enzyme linked immunosorbent filtration assay (ELIFA) has been developed for secretory leucocyte proteinase inhibitor (SLPI) utilising polyclonal anti-recombinant SLPI (anti-rSLPI) and polyclonal anti-bronchial mucus proteinase inhibitor (anti-BLPI) IgG samples. Millipore HATF nitrocellulose 96-well plates were used as receptacles for the assay and a commercial goat anti-rabbit IgG alkaline phosphatase conjugate was used as a secondary antibody for quantitation of levels of primary antibodies bound to rSLPI in the plate wells. Antigen bound to the HATF plates efficiently and the washing/blocking steps were simplified by vacuum filtration of samples resulting in a rapid and convenient assay system. The ELIFA was also sensitive and a detection limit of 0.1 ng SLPI/well was achieved using either anti-SLPI or anti-BLPI as primary antibodies. This assay was used to demonstrate the production of SLPI at moderate levels (0.5-3 ng/ml media) by human articular chondrocytes grown in monolayer culture.