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Many of the infections caused by group A streptococci and Staphylococcus aureus depend upon these organisms' ability to produce exotoxins. Pyrogenic toxin superantigens, a large family of serologically distinct, three-dimensional, structure-related proteins, are an example of such exotoxins. Pyrogenic toxin superantigens cause illnesses such as toxic shock syndromes and scarlet fever and have been strongly implicated in Kawasaki syndrome, arthritis, guttate psoriasis, and atopic dermatitis. Many, if not all, of the toxins' effects are caused by their alteration of the immune system cells, leading to CD4+ T-lymphocyte and macrophage activation.