Reactivity of human antibodies with pgp3 and control fusion proteins on Western blot. (A) GST fusion proteins as listed on top of the figure were analyzed in SDS gel (panel a) and parallel gels were blotted onto nitrocellulose membrane for reacting with the pooled positive human antiserum at various dilutions as listed along the left of the figure. The primary antibody reactivity was visualized with a goat anti-human IgG conjugated with HRP in ECL as described in the method section. The corresponding protein bands were indicated on the right of the figure. Note that the pooled human antiserum only minimally reacted with the pgp3 band at 1:4,000 (panel b) while remaining reactive with CPAF even after 1:1,000,000 dilution (panel f), suggesting that the human anti-pgp3 antibodies are highly conformation-dependent.