Kinetics of the local and systemic antibody response to primary and secondary infection with S48 Toxoplasma gondii in sheep

Summary Vaccination of sheep with live tachyzoites of Toxoplasma gondii , strain S48, affords protection against subsequent challenge with the parasite, but the mechanisms of immunity have not been fully determined. To understand better the nature of the antibody response the kinetics of both local and systemic antibody production were monitored in vaccinated sheep by means of an enzyme-linked immunosorbent assay and Western blotting. Local specific IgG production was analysed in efferent lymph obtained from the cannulated pre-femoral lymph node draining the site of infection. Antibody in efferent lymph plasma and peripheral blood serum from animals vaccinated with S48 tachyzoites was monitored and compared with IgG production in vaccinated sheep given a secondary tachyzoite challenge. Secondary challenge resulted in a clear immunological memory response, antibody being detected in the lymph 3 to 4 days after infection as compared with 7 to 8 days after a primary infection. IgG production was dominated by antibody recognizing a protein with an apparent molecular weight of 30 kDa, but other antigens (32, 24 and 11 kDa) were also readily detected.