Figure 4.

Antibody response in lambs immunized with A. phagocytophilum MSP4 and MSP4-HSP70 proteins. Groups of three lambs each were immunized with recombinant MSP4, MSP4-HSP70 combination or adjuvant/saline control and experimentally infected with a sheep isolate of A. phagocytophilum. An indirect ELISA test was performed to detect IgG antibodies against (A) MSP4 and (B) HSP70 proteins in immunized and control lambs using serum samples collected before each immunization and at 0, 7, 10, and 94 dpi. Antibody titers were expressed as OD_450nm (OD_lambsera−OD_PBScontrol). The results were compared between immunized and control groups by two-way ANOVA test (^*P < 0.05; N = 3 replicates per treatment). (C) The antigen-specific IgG antibody response in immunized lambs was corroborated by ELISA using pooled sera collected at 0 dpi, but incubating sera with different concentrations of A. phagocytophilum purified from infected HL60 human cells.