Abstract: A filter (10, 10a) includes a housing (12, 12a) extending along an axis (14). and having an inlet (16, 16a) at one axial end (18, 18a) of the housing and having an outlet (20, 20a) at a distally opposite axial end (22, 22a) of the housing. One or more pleated filter elements (44, 44a, 44b, 44c, 44d) in the housing are pleated along a plurality of bend lines (46, 48) extending axially. The filter element has a plurality of wall segments (50) extending in serpentine manner between the bend lines. The wall segments extend axially between upstream ends (52) and downstream ends (54) and define axial flow channels (58, 62) therebetween. The upstream ends of the wall segments are alternately sealed (56) to each other to defme a first set of flow channels (58) having open upstream ends (60), and a second set of flow channels (62) interdigitated with the first set of flow channels and having closed upstream ends (64).