Gene

World Wide Web

Engineering

Schistosomiasis

Ecology

Foreign body granuloma

Schistosoma mansoni

Biology

Parasite hosting

Eggshell

Biochemistry

Computer science

Immunology

Immune system

Helminths

Schistosoma

Antigen

Granuloma

Microbiology

Transmission (telecommunications)

Zoology

Electrical engineering

Zebrafish

Cell Host & Microbe

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.

Schistosoma mansoni Eggs Modulate the Timing of Granuloma Formation to Promote Transmission