Microbial superantigens are molecules expressed by bacteria and other microorganisms that have the power to stimulate a strong immune response by activation of T-cells. These molecules generally have regions that resemble self-antigens that promote a residual autoimmune response – this is the theory of molecular mimicry. Staphylococcal and streptococcal superantigens have been characterized in autoimmune diseases – the classical example in post group A streptococcal rheumatic heart disease, where there is similarity between M proteins of Streptococcus pyogenes to cardiac myosin and laminin. It has also been shown that up to 70% of patients with granulomatosis with polyangiitis are chronic nasal carriers of Staphylococcus aureus, with carriers having an eight times increased risk of relapse.  This would therefore be considered a type II hypersensitivity reaction.