Western blotting of proMBP and MBP in IL-5–induced UCC and peripheral blood eosinophils. (a) ProMBP with a major band at 33 kD detected with an anti-proMBP specific monoclonal antibody, J163-15E10. (b) MBP and a processed form of proMBP at 18 kD detected with the anti-MBP specific monoclonal antibody, J6-8A4. Lanes 1 to 5 were loaded with equivalent cell lysates from UCC at days 0, 6, 12, 18, and 24, respectively. Lane 6 was loaded with an equivalent cell lysate from purified peripheral eosinophils, and lane 7 contained 5 μg recombinant proMBP.28