Immunoblot analysis. Purified recombinant proteins for genes 16 and 19 of the Arkansas isolate, a recombinant antigen of a homologous gene from E. canis (ORF1) (24), and a whole-cell E. chaffeensis Arkansas isolate protein fraction were tested by Western blot analysis by using serum obtained from a B6 mouse immunized with live E. chaffeensis Arkansas isolate. (A) Coomassie blue stained gel; (B) corresponding immunoblot. Lanes: M, protein markers; E.ca, E. canis recombinant antigen; 16 and 19, the recombinant antigens made from E. chaffeensis isolate Arkansas 28-kDa OMP genes 16 and 19, respectively; E.ch, whole-cell antigen of E. chaffeensis isolate Arkansas.