Evasion Strategies of Microorganisms
There are three principal mechanisms by which complement controls invasion by microorganisms(Frank 1988). Binding of complement to the surface of an organism leads to the sequential activation of components C5 to C9 with formation of a complex of these proteins (the membrane attack complex). The complex has a hydrophobic surface and inserts into cell membrane lipid of the microorganism. This cylinder like structure has a hydrophilic central axis and destabilizes the osmotic regulation of the organism causing cell death. In the case of gram negative organisms, insertion of the C5b-9 complex appears to occur principally in the outer membrane. The precise mechanisms for dissolution of the inner or cytoplasmic membrane is unknown and the ultimate cause of death of these organisms is unknown(Taylor 1988). Enveloped viruses may have typical complement lesions formed in their membranes upon attack leading to loss of viral integrity(Cooper 1986). Parasites such as, promastigotes of Leishmania and Schistosoma mansoni cercaria undergo direct membrane attack and dissolution(Joiner 1988).
KeywordsSialic Acid Classical Pathway Complement Protein Schistosoma Mansoni Membrane Attack Complex
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