FIG. 7.

Anti-VR4 serum antibody binds only MSP1b proteins bearing the homologous VR4. Purified MSP1bF2 (lanes 4), MSP1bF3 (lanes 3), and MSP1bF4 (lanes 2), and, as a negative antigen control, B. bigemina RAP-1 (lane 1) were electrophoresed on SDS-containing polyacrylamide gels and then transferred to nitrocellulose. Membranes were reacted with a 1:1,000 dilution of serum from a mouse immunized with the VR4 region of MSP1bF3 (left panel) or normal mouse serum (right panel). Positions of molecular size markers are given in the right margins.