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The role of neutrophils in mediating host inflammation was examined in mice vaccinated with living third-stage infective hookworm larvae (L 3 ). Mice were vaccinated by oral immunization with 500 L 3 ( 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. L 3 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 L 3 within 2 h, and over 55% of the L 3 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 L 3 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 L 3 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 L 3 -vaccinated mice.

The role of peritoneal macrophages in a murine model of immunity to living hookworm third-stage larvae (L3) was investigated. Mice immunized orally with 500 L3 once every 2 weeks for three times were challenged intraperitoneally with 2000 L3 1 week after the final immunization. The challenged larvae were collected from the peritoneal cavity at intervals between 2 and 72 h and then examined by inverted light microscopy, scanning electron microscopy and transmission electron microscopy. Peritoneal cellular responses in non-immunized mice served as negative controls. The numbers of peritoneal macrophages in immunized mice were 6–7-fold higher than in non-immunized mice. In the peritoneal cavity of immunized mice, host macrophages adhered to the challenged L3 within 2 h and created a cocoon-like encasing which surrounded the parasite. Extensive damage to the L3 was observed which included swelling, collapse and deformation of the larval cuticle. Lysis and vacuolization of the parasite's internal structures were also observed. In contrast, no significant cellular adherence and damage were observed in L3 recovered from non-immunized mice. L3-specific antibody levels were also elevated in the peritoneum of immunized mice relative to non-immunized controls. These studies implicate macrophages as important effector cells in hookworm larval vaccine immunity.