Schistosome eggs provoke the formation of granulomas, organized immune aggregates, around them. For the host, the granulomatous response can be both protective and pathological. Granulomas are also postulated to facilitate egg extrusion through the gut lumen, a necessary step for parasite transmission. We used zebrafish larvae to visualize the granulomatous response to Schistosomamansoni eggs and inert egg-sized beads. Mature eggs rapidly recruit macrophages, which form granulomas within days. Beads also induce granulomas rapidly, through a foreign body response. Strikingly, immature eggs do not recruit macrophages, revealing that the eggshell is immunologically inert. Our findings suggest that the eggshell inhibits foreign body granuloma formation long enough for the miracidium to mature. Then parasite antigens secreted through the eggshell trigger granulomas that facilitate egg extrusion into the environment. In support of this model, we find that only mature S. mansoni eggs are shed into the feces of mice and humans.

血吸虫卵在其周围引起肉芽肿，有组织的免疫聚集物的形成。对于宿主，肉芽肿反应可以是保护性的和病理性的。肉芽肿也被假定为促进卵通过肠腔挤出，这是寄生虫传播的必要步骤。我们使用斑马鱼幼虫来可视化肉芽肿对血吸虫的反应鸡蛋和惰性鸡蛋大小的珠子。成熟的卵迅速募集巨噬细胞，巨噬细胞在数天内形成肉芽肿。珠还通过异物反应迅速诱发肉芽肿。令人惊讶的是，未成熟的卵不会募集巨噬细胞，表明卵壳具有免疫学惰性。我们的研究结果表明，蛋壳抑制异物肉芽肿的形成时间足够长，以使灵​​acid成熟。然后，通过蛋壳分泌的寄生虫抗原会引发肉芽肿，从而促进卵子进入环境。为了支持该模型，我们发现只有成熟的曼氏葡萄球菌卵会掉入小鼠和人类的粪便中。