The interaction of Schistosoma mansoni
with its host's
immune system is largely affected by multiple specific and
non-specific evasion mechanisms employed by the
parasite to reduce the host's immune reactivity. Only little
is known about these mechanisms on the molecular level. The four
molecules described below are intrinsic parasitic proteins recently
identified and studied in our laboratory.
1. m28 - A 28kDa membrane serine protease. m28 cleaves iC3b
and can thus restrict attack by effector cells utilizing complement
receptors (especially CR3).
Treatment with protease inhibitors potentiates killing of
schistosomula by complement plus neutrophils.
2. Smpi56 - A 56kDa serine protease inhibitor. Smpi56 binds
covalently to m28 and to neutrophil's elastase and blocks their
proteolytic activity.
3. P70 - A 70kDa C3b binding protein. The postulated
activity of P70 includes binding to C3b and blocking of complement
activation at the C3 step.
4. SCIP-1 - A 94kDa schistosome complement inhibitor. SCIP-1
shows antigenic and functional similarities to the human 18kDa
complement inhibitor CD59. Like CD59, SCIP-1 binds to C8 and C9
and blocks formation of the complement membrane attack complex.
Antibodies directed to human CD59 bind to schistosomula and
potentiate their killing by complement.
The structure and function of these four proteins as well as
their capacity to induce protection from infection with S. mansoni
are under investigation.
