Macrophage proliferation and activation during Toxoplasma gondii infection in mice: relationship to lymphocyte stimulation.

Macrophage proliferation and activation as well as lymphocyte stimulation in the peritoneal cavities of mice were investigated during the course of a Toxoplasma gondii (Beverly strain) infection. Macrophage proliferation had started already after day one and reached a first peak on day 2 (3H-thymidine labelling index approximately 6%). This proliferation was not accompanied by any notable lymphocyte stimulation. An equally high L.I. for macrophages was found after injection of 0.9% saline. From day 3-4 and peaking on day 7-11, a considerable blastoid transformation of lymphocytes occurred (maximum L.I. for lymphoid cells approximately 20% on day 7). In parallel with this blastoid response, a substantial macrophage proliferation took place (L.I. approximately 8%). Large numbers of activated macrophages also appeared during this period, DNA synthesizing cells were found even among the most highly activated macrophages. The results indicated that the early and the late macrophage proliferations were stimulated by different mechanisms.