In vitro blastogenesis of equine lymphocytes by inactivated equine adenovirus type 1 antigen

An inactivated equine adenovirus type 1 (EAdV1) vaccine was administered to 4 horses. The horses had virus-neutralizing (VN) antibody titers before they were vaccinated, but developed higher VN antibody titers in response to vaccination. Nonvaccinated control horses did not show increases in VN antibody during the study, indicating that any increase in antibody titer in vaccinated horses was a result of vaccination and not due to an EAdV1 epizootic during the study. Specific EAdV1 in vitro lymphocyte blastogenesis (LB) was evaluated, using lymphocytes from 4 vaccinated and 2 control horses. Horses were vaccinated on days 0 and 14, and the LB assays were conducted on days -4, 0, 3, 7, 10, 14, 17, 21, 24, and 28. Lymphocytes from horses were incubated for 4 days with 2 concentrations of inactivated, concentrated and purified EAdV1 antigen. The LB responses for the 2 control horses showed no significant changes during the study period (maximum stimulation indices to EAdV1 antigen for individual horses were between 2.8 and 3.6). The 4 vaccinated horses showed marked increases in stimulation indices in response to EAdV1 antigen (maximum stimulation indices, between 5.3 and 18.6). In control assays, identical lymphocyte preparations from all horses responded normally to phytohemagglutinin.