Schistosoma mansoni evacuates its eggs through Peyer’s patches

Schistosomes are parasitic worms that live in the blood and have a complicated life cycle. The sexual form inhabits vertebrates (humans included) whereas the other stages infest fresh water snails. Adult worms tend to chronically infect their host (sometimes for many years) but for the propagation they have to be able to release their eggs to the outer environment. These blood parasites are remarkably invisible to the immune system; however, their eggs are known to induce the immune response. How such ability may connect to the propagation issue is the subject of the recent publication.

The link: http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003063

Authors study how Schistosoma mansoni, which is an endemic human parasite present in many tropical regions of the world, may excrete its eggs through the intestinal barrier (schistosome species vary between utilization of the intestinal and urinary tracts as the evacuation routes for eggs). It looks like to this end the parasite uses the lymphatic structures encountered in the lower portion of the small intestine – Peyer’s patches. The presence of mature schistosome eggs is apparently able to remodel the vasculature around Peyer’s patches and introduce changes to the cellularity of these intestinal lymphatic structures. Moreover and crucially, in the strain of mice that harbors no Peyer’s patches the egg excretion is visibly reduced and more eggs appear to be backwashed into the host tissue where they form granulomas.

For a number of years schistosome eggs have been hyped as the “taming agent” of the over-reacting immune system. It is well known that they possess the modulatory influences over a number of inflammatory conditions that afflict the gastrointestinal tract. I wonder if such an ability to modulate may be due to the described peculiar interaction of schistosome eggs with their hosts’ Peyer’s patches. From the schistosome point of view eggs need to get out. Thus the parasite may have evolved to drive the immune reaction to its eggs because of the necessity to utilize immune structures for the egg excretion.

Joseph D. Turner,Priyanka Narang,Mark C. Coles,Adrian P. Mountford (2012). Blood Flukes Exploit Peyer’s Patch Lymphoid Tissue to Facilitate Transmission from the Mammalian Host PLOS Pathogens

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