Schistosoma worms are experts at concealment, but now researchers have revealed one of their biggest secrets. Two groups have nabbed a long-sought protein in the worms’ eggs that polarizes helper T cells.
The eggs that female schistosome worms pump out at a rate of 300 per day can spark a Th2 response. This immune reaction appears to be a lifesaver for the host, as parasitized mice that can't activate Th2 die from excessive inflammation. However, pinning down the polarization trigger has been tricky because an egg secretes several hundred proteins.
Using different techniques, the two groups homed in on an RNA-slicing enzyme called omega-1. After pinpointing the size of the Th2 trigger, Steinfelder et al. (page 1681) purified the protein from the supernatant of worm egg cultures, which was easier to sift through because it contains fewer kinds of proteins than whole egg extracts. Everts et al. (page 1673) simply went after the most abundant egg secretions, omega-1 and another protein called IPSE/α-1. In cultures of human dendritic and helper T cells, omega-1 was a Th2 polarizer, whereas IPSE/α-1 wasn't.
The studies also offer some clues about how omega-1 works. Steinfelder et al. found that the protein inhibits interactions between dendritic cells and T cells, perhaps mimicking the antigen-scarce situation that favors the Th2 shift. Still uncertain, however, is whether omega-1 exerts its effects through a receptor, through its enzymatic activity, or through both routes. And the protein probably doesn't act alone. Everts et al. showed that egg extracts lacking omega-1 could still trigger polarization if injected into mice. ML