Anti-Id titer induced by immunization with Id fusion proteins.

Mice were immunized twice by subcutaneous or intraperitoneal injection of 50 μg of Id, Id-GM, or Id-CTLA4, and bled 2 weeks after each immunization. Anti-Id titers in sera after the first (A) or second (B) immunization were determined by ELISA, as described in “Materials and methods.” The data are presented as the mean ± SD for 5 animals of each group.