Abstract
Defining conserved, protective epitopes is essential to the design of an effective vaccine against bovine anaplasmosis. MSP4, one of six initial body proteins recognized by a neutralizing serum, is conserved among Anaplasma marginale isolates at both the protein and the DNA levels. Sera from cattle immunized with an outer membrane fraction of A. marginale and protected from a virulent challenge bind MSP4. The gene for MSP4 has been cloned, and the recombinant protein has been expressed, isolated, and demonstrated to share epitopes with the native protein expressed on initial bodies. MSP4 may have a greater potential to protect cattle from a challenge by heterologous isolates than other A. marginale surface proteins, which vary widely in size and structure.