Most cases of scarlet fever occur in children. Adults have usually developed immunity to a toxin that the Streptococcus bacteria produce during infection. Explain how an adult develops immunity to the toxin.

Previous exposure to the toxin confers immunity by eliciting an immune response whereby b-cells differentiate into plasma cells allowing the production of antibodies. These will in turn stimulate production of B-memory cells which will elicit an immediate response once the toxin is recognised.