FIG. 1.

I-E2 induces higher anti-E2 NOB titers than S-E2 does. (A) E2₇₁₅ protein was expressed in CHO cells and purified from the supernatant (S-E2) and from lysed cells (I-E2). The two fractions were analyzed by SDS-PAGE (10% acrylamide) under reducing conditions and Western blotting with chimpanzee anti-E1/E2 antiserum. The sizes (in kilodaltons) of protein molecular mass markers are indicated on the left. (B and C) Hartley female guinea pigs were immunized i.p. with 8 μg of S-E2 or I-E2 in MF59-0 adjuvant on days 0, 30, and 90. Sera taken on day 110 were analyzed by ELISA (B) and the NOB assay (C). Anti-E2 ELISA titers (total IgG) are expressed as the highest serum dilution resulting in an OD₄₅₀ that equaled the cutoff (mean OD + 3 standard deviations for eight preimmune sera). Anti-E2 NOB titers are expressed as reciprocal values of serum dilutions which inhibit 50% of E2 binding to CD81 on MOLT-4 cells. The results are given as the mean values for five individual animals.