PRIMARY AND SECONDARY RESPONSES OF THE OVINE LYMPH-NODE TO TOXOPLASMA-GONDII - CELL OUTPUT IN EFFERENT LYMPH AND PARASITE DETECTION

Efferent lymphatic cannulation was used to study the dissemination of strain S48 of Toxoplasma gondii and the cell output from the prefemora l lymph node, after infection of both ''naive'' and vaccinated sheep. In the former the mean cell output decreased for 3 days before reachin g a peak at 11 and 12 days, but in vaccinated ewes a similar drop in c ell output and subsequent peak occurred significantly earlier, at 24h and 5 days, respectively. The cellular response in both types of sheep was largely due to a marked increase in blast cells. The detection of live toxoplasms and parasite DNA by mouse inoculation and the polymer ase chain reaction, respectively, gave similar results; the parasite w as demonstrated in lymph from days 3 to 12 during a primary infection but with a sharp cut-off after day 9 coinciding with the peak blast ce ll response. Very little evidence of T. gondii was found in lymph of v accinated sheep after challenge. Immunity, which is thought to be larg ely T-cell mediated and is sustained without continuous antigenic stim ulation, suppresses dissemination of the parasite in the lymph and the refore to other sites, which might include the gravid uterus.