Reactivity of immune sera in the LELDKWAS epitope ELISA. Three BALB/c mice each were injected subcutaneously with 50 μg (estimated by SDS–PAGE) of native or heat/SDS-denatured protein in complete Freund’s adjuvant followed by two boosts in incomplete Freund’s adjuvant at 2-week intervals. Two weeks after the last immunization, serum samples were collected, pooled and heat-inactivated. Twofold serial dilutions of immune sera raised against native or denatured chimeric L1 proteins D, E or F, or dilutions of MAb 2F5 (1 ng/ml) were reacted against the LELDKWAS peptide fused to the C terminus of AP, expressed in and affinity-purified from E. coli and attached to ELISA plates. OD, absorbance at 405 nm.