MASP interactions with plasma-derived MBL.

The interaction of mannan-binding lectin (MBL) with its associated serine proteases (MASPs) was investigated using recombinant (r) MBL, plasma-derived (pd) MBL, rMASP-3 and rMAp19. When mixed with MBL-deficient serum, rMBL and pdMBL associated with free MASP-2 to (re)gain complement-activating activity. MASPs already associated with pdMBL did not exchange with rMASP-3 or rMAp19, which bound to non-overlapping sites on MBL. Thus, rMASP-3 and rMAp19 bound to free available sites on rMBL and pdMBL. These results have important implications for the therapeutic use of MBL preparations.