Schistosoma Mansoni - Evasion of Host Immunity

Evasion of Host Immunity

Adult and larval worms migrate through the host's blood circulation avoiding the host's immune system. The worms have many tools that help in this evasion, including the tegument, antioxidant proteins, and defenses against host membrane attack complex (MAC).

Tegument

The tegument coats the worm and acts as a physical barrier to host antibodies and complement.

Antioxidant proteins

Host immune defenses are capable of producing superoxide, which has a tremendous detrimental effect on the worm. However, they are able to produce a number of antioxidant proteins that block the effect of superoxide. Schistosomes have four superoxide dismutases, and levels of these proteins increase as the schistosome develops and matures.

Antioxidant pathways were first recognised as a chokepoints for Schistosomes and later extended to other trematodes and cestodes. Targeting of this pathway with different inhibitors of the central antioxidant enzyme Thioredoxin Glutathione Reductase (TGR) results in reduced viability of worms

Defense against host MAC

Schistosomes have evolved ways to block host complement proteins. Immunocytochemistry techniques have found decay accelerating factor (DAF) protein on the tegument. DAF is found on host cells and protects host cells by blocking formation of MAC. It has also been found that the schistosome genome consists of human CD59 homologs. CD59 inhibits MAC.