FILTER FOR LEUCOCYTE SEPARATION

PROBLEM TO BE SOLVED: To make a filter have good removing performance and hard to be clogged, by raising the concentration of a quaternary ammonium salt toward downstream in a filter comprising specific kinds of surface fixed porous substrates with different concentrations of a quaternary ammonium salt. SOLUTION: This filter for leucocyte separation is constituted of more than three kinds of surface fixed porous substrates with different concentrations of a quaternary ammonium salt, and the concentration of the quaternary ammonium salt is raised toward downstream. The substrate 1 comprises (1) a porous substrate layer with cationization degree of 0, (2) a porous substrate layer with a cationization degree of 0.2-0.5, and (3) a porous substrate layer with a cationization degree of 0.6-1.0 and higher by 0.2-0.6 than that of (2). Further, the substrate layers are placed from the upstream side of a blood flow passage in the order of (1) the porous substrate layer with cationizaton degree of 0, (2) the porous substrate layer with cationization degree of 0.2-0.5, and (3) the porous substrate layer with cationization degree of 0.6-1.0 and higher by 0.2-0.6 than that of (2).