Nonspecific suppression of initiation of memory cells in Toxoplasma gondii-infected mice

The effect of Toxoplasma infection on initiation and expression of memory cells to dinitrophenol (DNP)-conjugated protein antigens in humoral immune responses was studied in mice. Marked suppression in the initiation of memory cells to DNP-conjugated keyhole limpet hemocyanin occurred in the acute phase of infection. However, once the memory cells were induced before infection, expression of the memory cells was not affected. Moreover, the suppression of priming occurred on both T and B cells. The suppressive effect was observed in all immunoglobulin classes tested, i.e., immunoglobulin M (IgM), IgG1, IgG2, and IgE, regardless of the four kinds of DNPO-conjugated protein antigens. This nonspecific suppression could be induced only by living toxoplasmas, by either the perioral or parenteral route, but not by lysed organisms. A transfer of normal spleen cells could not restore the ability of infected mice to initiate memory cells. Furthermore, the suppressive effect of the infected mice was not removed by 400 R of γ-irradiation. These results suggested that irradiation-resistant suppressor cells cause nonspecific suppression of the initiation of memory cells in Toxoplasma-infected mice.