Electron and light microscopy of neutrophil responses in mice vaccinated and challenged with third-stage infective hookworm (Ancylostoma caninum) larvae.

The role of neutrophils in mediating host inflammation was examined in mice vaccinated with living third-stage infective hookworm larvae (L₃). Mice were vaccinated by oral immunization with 500 L₃ (Ancylostoma caninum) once every 2 weeks for a total of three immunizations. The vaccinated mice were then challenged intraperitoneally with 2000 L_3, 1 week after the final immunization. To stimulate peritoneal production of neutrophils, 2 ml of 2% glycogen were injected intraperitoneally at 16 h prior to the challenge infection. Neutrophils were found to comprise 85% of the peritoneal cell population. L₃ from the challenge infection were collected and then examined at timed intervals by inverted light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Greater than a fivefold increase in the total numbers of peritoneal cells was noted in the vaccinated mice as compared to unvaccinated mice. In the peritoneal cavity of vaccinated mice, the neutrophils adhered to the L₃ within 2 h, and over 55% of the L₃ were surround by clusters of neutrophils to form a sausage-like sheath 4 h later. At 24–72 h after challenge, almost all of the L₃ recovered from the vaccinated mice were covered with thick clusters of cells. Both SEM and TEM demonstrated extensive ultrastructural damage to the L_3. In contrast, the L₃ recovered from the unvaccinated mice appeared to be unaffected by neutrophils. These studies suggest that neutrophils, like macrophages, can have an important role as effector cells in L₃-vaccinated mice.