Question

Rapid polymorphism of antigenic makeup is one of the microbial evasion strategies, what does that means?, what would be the complications of this on the immune system? and search for an example of a pathogen have this kind of evasion. (100 – 150 words)

Answer 1

Rapid polymorphism of the antigen is nothing but the antigenic variations incurred by the microbe to evade the hosts immune system. The term polymorphism is nothing but the ability of a gene or protein to take up many forms which is usually as a result of mutation, site specific DNA inversions or recombination of genes. In technical terms, Antigenic variation refers to the expression of functionally conserved moieties within a clonal population that are antigenically distinct.

Antigen is the part recogonized by the anitbodies of the immune system upon invasion of microbes. When microbes undergo antigenic variations the antibodies will not recogonize the newly modified allele of the known antigen of the microbe to which the immune system has been already exposed. This is a challenge to not only the newly infected but also is capable of causing reinfection to the already infected.

Neisseria gonorrhoeae is one common example of anitgenic variations. Many pathogenic organisms use homologous recombination to vary surface antigens to avoid immune attack. Neisseria gonorrhoeae antigenic variation occurs by changing the properties of its surface pili in a process called pilin antigenic variation (AV) which takes place by high-frequency gene conversion reactions that transfer silent pilS sequences into the expressed pilE locus and requires the formation of an upstream guanine quartet (G4) DNA structure to initiate this process. The MutS and MutL proteins of the mismatch correction (MMC) system act to correct mismatches after replication and prevent homeologous (i.e., partially homologous) recombination, but MutS orthologs can also bind to G4 structures. Neisseria gonorrhoeae continually changes its outer surface proteins to avoid recognition by the immune system.