Histological Observations with Respect to the Immune Mechanism in Eimeria acervulina Infection in the Domestic Fowl

Summary A strong repulsion of epithelial tissue into the intestinal lumen associated with a lowered intestinal pH, thin liquid intestinal contents and leakage of serumprotein into the lumen was observed in E. acervulina immunized birds, some hours following oral reinfection. The extruded epithelial tissue degenerated and died in the lumen; massive numbers of dying cells could also be observed in tissue sections of the intestinal contents. Most likely the sporozoites are pushed off together with the cells. The repulsion was always associated with a prominent swelling of the muscles in the intestinal villi. In the not immune birds however, some cell repulsion and a little swelling of the villous muscles was observed but only at the tips of the villi. In the normal not infected individual contraction of the villous muscles supports the physiological repulsion of epithelial cells at the so called extrusion zone.In the immunized birds the reaction of the tissue after reinfection could be completely suppressed by cortisone treatment.Incubation experiments of intestinal pieces both from immunized and not immunized birds with oocyst fluid, sporocysts and glucose in vivo as well as in vitro showed reactions in the same way as mentioned above. The reaction was much stronger in the immunized than in the not immunized birds. These results indicate a local tissue immunity.The hypothesis is given that after a primary infection compounds stay behind in the intestinal wall enhancing the reaction of oocyst fluid and sporocysts with glucose to such an extent that much lactic acid is formed, which in turn might affect the intestinal wall, resulting in repulsion of the epithelial tissue.