Immunization of Bovines Using a DNA Vaccine (pcDNA3.1/MSP1b) Prepared from the Jaboticabal Strain of Anaplasma marginale

doi:10.1196/annals.1307.040

Anaplasma is a tick-borne ehrlichial pathogen of cattle thatcauses the disease, anaplasmosis. In the present study, a totalof 11 Anaplasma marginale seronegative calves were assignedinto two groups: one immunized (G1, n = 6) and one nonimmunized-control(G2, n = 5). Six calves were immunized by using a DNA vaccinecontaining the gene of a major surface protein, MSP1b, encodedby the plasmid identified as pcDNA3.1/MSP1b. Calves receivedthree intramuscular inoculations of 100 µg of pcDNA3.1/MSP1bat a 20-day interval. The control group received buffer phosphateat the same schedule as the experimental group. The immune responseelicited by immunization with pcDNA3.1/MSP1b was evaluated inmice and calves. Twenty days following initial immunization,specific serum antibody from four BALB/c mice bound MSP1b inimmunoblots. Sixty days after the last immunization, all calveswere challenged with cryopreserved A. marginale at a dose of10⁴ parasites/mL/animal by intravenous injection. Results ofpacked cell volume (PCV) and detection of infected erythrocytesin all experimental groups revealed that the decrease of PCVand detection of infected erythrocytes occurred at 28 to 42days after challenge. Mean temperature values did not increaseover 39.85°C. Antibodies developed by immunized bovinesfrom G2 were detected 14 days after challenge. MSP1b was characterizedduring the immunization period and MSP2 was the most predominantpolypeptide at the challenge period. DNA of A. marginale wasdetected in all groups just after challenge by nested PCR assay.It can be concluded that all immunized bovines were partiallyprotected against homologous challenge.