Suppressive effect of secondary Toxoplasma gondii infection on antibody responses in mice.

The effect of the secondary infection with Toxoplasma gondii on antibody responses to unrelated antigens was examined in mice. A reinfection with 5 X 10(3) organisms did not affect either primary anti-sheep erythrocyte antibody responses, or anti-dinitrophenol antibody responses to dinitrophenylated keyhole limpet hemocyanin. With an increase of the reinfection dose to 2.5 X 10(4) organisms, suppression of anti-sheep erythrocyte antibody responses was induced. By contrast, in the primary infection, the anti-sheep erythrocyte and anti-dinitrophenol antibody responses were markedly suppressed by an injection with only 5 X 10(2) or 1 X 10(3) T. gondii organisms. Plastic-adherent cells of spleens from mice reinfected with 2.5 X 10(4) organisms showed a strong suppressor activity in an in vitro primary anti-sheep erythrocyte antibody response system. These results demonstrate that a nonspecific suppression of antibody responses is provoked by a secondary T. gondii infection, only when mice receive a large number of organisms in the reinfection, and the suppressed antibody responses seem to be caused by an activation of suppressor cells that adhere to plastic.