KINETICS OF THE LOCAL AND SYSTEMIC ANTIBODY-RESPONSE TO PRIMARY AND SECONDARY INFECTION WITH S48 TOXOPLASMA-GONDII IN SHEEP

Vaccination of sheep with live tachyzoites of Toxoplasma gondii, strai n S48, affords protection against subsequent challenge with the parasi te, 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 vaccinat ed 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 c ompared with IgG production in vaccinated sheep given a secondary tach yzoite challenge. Secondary challenge resulted in a clear immunologica l memory response, antibody being detected in the lymph 3 to 4 days af ter 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 1 1 kDa) were also readily detected.