Filter sterilization of highly infectious samples to prevent false negative analysis of matrix metalloproteinase activity

Matrix metalloproteinases (MMPs) are implicated in the immunopathology of numerous infectious diseases. High risk samples such as those generated after infection with Mycobacterium tuberculosis require filter sterilization for safe analysis of MMP concentrations. Here, we report that commercial filter membranes may cause artefacts by binding MMPs. Anopore 0.2 μM membrane filtration reduced MMP-1 concentrations to undetectable levels by zymography and Western blotting. Polypropylene 0.45 μM filtration removed some MMP-1, while Polysulphone, Durapore and Bio-inert 0.2 μM membranes did not remove MMP-1. Anopore filtration also removed all MMP-7 and -9 activity, suggesting that the conserved MMP catalytic domain binds the membrane. This study demonstrates the importance of selecting the appropriate filter in MMP analysis to avoid incorrectly excluding MMP involvement in infection-related immunopathology.