Microbial complement inhibitors as vaccines.

Complement inhibiting surface proteins of pathogenic bacteria provide candidates for vaccines because of two reasons. First, an immune response against them would recognize the microbes and secondly, it would neutralize the key bacterial virulence mechanism. Prerequisites for a vaccine protein include the following: (i) it should show limited variability, (ii) it should be immunogenic and the immune response against it should cover a sufficiently broad range of microbial strains, (iii) it should not be hidden beneath a capsule, long LPS O-polysaccharide side chains or a protein coat and (iv) it should not raise unwanted immune responses against host structures. Bacterial complement inhibitors often act by binding the soluble inhibitors factor H or C4 bp, by blocking C3 or C5 activation or by enzymatically cleaving key complement components. Inhibitors have been found from all major types of pathogens and may offer promise as rational vaccine candidates for preventing diseases such as meningococcal meningitis, systemic pneumococcal or group B streptococcal disease and Lyme borreliosis.