Molecular cloning and characterization of the 120-kilodalton protein gene of Ehrlichia canis and application of the recombinant 120-kilodalton protein for serodiagnosis of canine ehrlichiosis

The 120-kDa outer membrane protein (p120) is a potential adhesin of Ehrlich ia chaffeensis, and recombinant p120 is very useful for serodiagnosis of hu man monocytotropic ehrlichiosis. The analogous gene of p120 in Ehrlichia ca nis was cloned, sequenced, and expressed. Like the E. chaffeensis p120, the E. canis p120 contains tandem repeat units. However, neither the repeat nu mber nor the amino acid sequences in the repeats are identical in the two E hrlichia species. The repeat units are hydrophilic and by probability analy sis are predicted to be surface exposed in both species. The repeat regions of the p120s of the two species have common amino acid sequences that are predicted to be surface exposed. The overall amino acid sequence of the E. canis p120 is 30% homologous to that off. chaffeensis p120. Protein immunob lotting demonstrated that the recombinant E. canis p120 reacted with conval escent sera from dogs with canine ehrlichiosis. These results indicate that the recombinant p120 is a potential antigen for the serodiagnosis of canin e ehrlichiosis.