Dose response curve of antibody production in immunized mice. Sera from 5 mice per group were collected 1 week after the last immunization and tested by ELISA for the presence of specific antibodies. The peptides from C1E1 and C1E2 represented amino acids 93-112 of the C1 region, whereas peptides C2E represented amino acids 218-240 of the C2 region. Antibody titers of sera from mice immunized with C1E1, C1E2, and C2E at 50, 100, and 200 μg, are expressed as the log2 values of reciprocal endpoint titers. The control group was injected with normal saline. The immunization by peptides C1E1 and C1E2 induced a poor antibody response, whereas peptide C2E induced a robust antibody response, in a dose dependent manner.