Respective role of antibodies and immune macrophages during acquired immunity against toxoplasmosis in mice.

Immunity of animals correlated with the destructive ability of their macrophages. Intraperitoneal inoculation of T. gondii led to a very limited infection of macrophages from immune mice. This infection was next rapidly and completely inhibited. Conversely, macrophages from mice immunized with killed toxoplasma were massively invaded and evolved like control cells. Similar results were also obtained with macrophage cultures infected in vitro and followed over a period of 4 days. Even after several washes, immune macrophages still preserved their ability to inhibit intracellular replication of toxoplasma. However, this resistance was not homogenous: in the absence of antibodies, some macrophages supported a parasitic growth whereas some others remained intact. Results have also shown that the engulfment capability of immune macrophages was not modified. The primary role of resistant macrophages in the immune response did not however exclude a participation of humoral factors. Specific antibodies acted on extracellular toxoplasma either by lysing them in the presence of the accessory factor or by slowing their active penetration into the cells. Furthermore, they did not affect the phagocytic activity of macrophages. The in vitro protective role of peritoneal exudate from immune mice seemed similar to that afforded by sera anti-toxoplasma antibodies.