Understanding how immunity to pathogens develops is crucial for progress in the
quest for effective vaccines. Intraspecies and interspecies cross-reacting antibodies are produced
in high frequency against immune-relevant and shared microbial epitopes. It has been
confirmed that cross-reactive antigens may have a crucial role in natural epidemiology to a
particular infection and that cross-protection may influence the outcome of natural infections.
On the other hand, the action of cross-reactive antibodies may be very harmful for the host. In
this review we discuss both the defensive and offensive capabilities of cross-reactive antibodies.
The defensive properties are discussed with regard to the beneficial cross-protective interaction
of these antibodies against various microorganisms including viruses, bacteria, fungi
and protozoan parasites. We summarize the current knowledge of numerous effector functions
of these antibodies such as agglutination, neutralization of infectivity, complement activation,
phagocytosis enhancement, and antibody-dependent cellular cytotoxicity. We also discuss the
offensive action of cross-reactive antibodies including their detrimental effects in exacerbation
of the infective diseases, as well as autoimmune diseases and allergy as a result of inappriopriate
or deleterious inflammatory response associated with host tissue destruction. The
factors influencing cross-protective capacity of antibodies are also presented.
Keywords: Antibodies, cross-reactivity, polyreactivity, cross-protection, molecular mimicry, immunity to pathogens,
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