Selective modification and immune evasion: a hypothesis.

A hypothesis is proposed asking why enzyme neutralization is not an effective host-response to a parasite despite the fact that some parasite housekeeping enzymes are highly immunogenic. It is hypothesized that although the structural domain can be immunogenic, the active sites of the parasite enzyme molecules have converged evolutionarily to resemble the functional part (active sites) of host's enzyme molecules, by structural modification/rearrangement (amino acid substitution/polypeptide chain folding) with the effect: (i) of functional adaptation to the host environment; and (ii) to escape detection of active sites by the host as non-self, allowing the parasite to be exposed to antiparasite enzyme antibodies, without deleterious effects on the parasite.