Superantigen - Evolution of Superantigen Production

Evolution of Superantigen Production

SAg production effectively corrupts the immune response, allowing the microbe secreting the SAg to be carried and transmitted unchecked. One mechanism by which this is done is through inducing anergy of the T-cells to antigens and SAgs. Lussow and MacDonald demonstrated this by systematically exposing animals to a streptococcal antigen. They found that exposure to other antigens after SAg infection failed to elicit an immune response. In another experiment, Watson and Lee discovered that memory T-cells created by normal antigen stimulation were anergic to SAg stimulation and that memory T-cells created after a SAg infection were anergic to all antigen stimulation. The mechanism by which this occurred was undetermined. The genes that regulate SAg expression also regulate mechanisms of immune evasion such as M protein and Bacterial capsule expression, supporting the hypothesis that SAg production evolved primarily as a mechanism of immune evasion.

When the structure of individual SAg domains has been compared to other immunoglobulin-binding streptococcal proteins (such as those toxins produced by E. coli) it was found that the domains separately resemble members of these families. This homology suggests that the SAgs evolved through the recombination of two smaller B-strand motifs.