Immune responses in infections with coccidia: macrophage activity.

Peritoneal exudate cells from chickens immunized with two species of coccidia, Eimeria tenella or Eimeria maxima, were examined for their capacity to phagocytose stages of the parasite in vitro. True phagocytosis of the sporozoite stage is difficult to estimate because of its ability to invade cells, but may be evaluated by comparison with control suspensions. Peak activity (compared with cells from coccidia-free chickens) was found 3 to 5 weeks after the first inoulum of oocysts of E. tenella, and 1 week after the first inoculum of E. maxima- times which correspond to the onset of complete immunity to infection. Cells from coccidia-free chickens, in the presence of serum from birds immunized with E. tenella, phagocytosed sporozoites of E. tenella in a similar manner to cells from immunized birds. The immune serum had both cytophilic and opsonic adherence properties and the latter was species specific (for the two species tested).