Recombinant major antigenic protein 2 of Ehrlichia canis: A potential diagnostic tool

The major antigenic protein 2 (MAP2) of Ehrlichia canis was cloned and expr essed. The recombinant protein was characterized and tested in an enzyme-li nked immunosorbent assay (ELISA) format for potential application in the se rodiagnosis of canine monocytic ehrlichiosis. The recombinant protein, whic h contained a C-terminal polyhistidine tag, had a molecular mass of approxi mately 26 kDa, The antigen was clearly identified by Western immunoblotting using antihistidine antibody and immune serum from an experimentally infec ted dog. The recombinant MAP2 (rMAP2) was tested in an ELISA format using 1 41 serum samples from E. canis immunofluorescent antibody (IFA)-positive an d IFA-negative dogs. Fifty-five of the serum samples were from dogs experim entally or naturally infected with E. canis and were previously demonstrate d to contain antibodies reactive with E. canis by indirect immunofluorescen ce assays. The remaining 86 samples, 33 of which were from dogs infected wi th microorganisms other than E. canis, were seronegative. All of the sample s from experimentally infected animals and 36 of the 37 samples from natura lly infected animals were found to contain antibodies against rMAP2 of E. c anis in the ELISA. Only 3 of 53 IFA-negative samples tested positive on the rMAP2 ELISA. There was 100% agreement among IFA-positive samples from expe rimentally infected animals, 97.3% agreement among IFA-positive samples fro m naturally infected animals, and 94.3% agreement among IFA-negative sample s, resulting in a 97.2% overall agreement between the two assays. These dat a suggest that rMAP2 of e. canis could be used as a recombinant test antige n for the serodiagnosis of canine monocgtic ehrlichiosis.