Abstract:
Parasitic infections induce host immune responses that eliminate the invading parasites.
However, parasites have evolved to develop many strategies to evade host immune
attacks and survive in a hostile environment. The complement system acts as the first
line of immune defense to eliminate the invading parasites by forming the membrane
attack complex (MAC) and promoting an inflammatory reaction on the surface of
invading parasites. To date, the complement activation pathway has been precisely
delineated; however, the manner in which parasites escape complement attack, as a
survival strategy in the host, is not well understood. Increasing evidence has shown
that parasites develop sophisticated strategies to escape complement-mediated killing,
including (i) recruitment of host complement regulatory proteins on the surface of the
parasites to inhibit complement activation; (ii) expression of orthologs of host RCA
to inhibit complement activation; and (iii) expression of parasite-encoded proteins,
specifically targeting different complement components, to inhibit complement function
and formation of the MAC. In this review, we compiled information regarding parasitic
abilities to escape host complement attack as a survival strategy in the hostile
environment of the host and the mechanisms underlying complement evasion. Effective
escape of host complement attack is a crucial step for the survival of parasites within the
host. Therefore, those proteins expressed by parasites and involved in the regulation of
the complement system have become important targets for the development of drugs
and vaccines against parasitic infections.
