The investigation of molecular mimicry through the use of monoclonal antibodies has identified other types of molecular mimicry. Molecular mimicry between host and bacterial antigens was first defined as identical amino acid sequences shared between different molecules present in tissues and the bacterium ( 26– 28). The identification of cross-reactive antigens in group A streptococci is important in our understanding of the pathogenesis of autoimmune sequelae, such as rheumatic fever including carditis ( 8, 11) and Sydenham chorea ( 7), which may follow group A streptococcal infection ( 3). The advent of monoclonal antibodies and T cell clones/hybridomas has greatly advanced identification of host and streptococcal antigens responsible for immunological cross-reactions associated with immunization, infection, and autoimmune sequelae. Immunological cross-reactions between streptococcal and host molecules have been identified by antibodies or T cells that react with streptococcal components and tissue antigens ( 6, 7, 22, 24, 25). Molecular mimicry is the term used to describe immunological cross-reactivity between host and bacterial antigens. The chapter elaborates on the discoveries that led to a better understanding of the pathogenesis of disease and provides an overview of the history and the most current thought about the immune responses against the host and streptococcal cross-reactive antigens in group A streptococcal sequelae.Ĭross-reactive antigens are molecules on the group A streptococcus that mimic host molecules and during infection or immunization induce an autoimmune response against host tissues leading to the autoimmune group A streptococcal sequelae ( 1– 25) 1–25). The sharing of host and streptococcal epitopes leads to molecular mimicry between the streptococcal and host antigens that are recognized by the autoantibodies during the host response. ![]() The pathogenesis of acute rheumatic fever, rheumatic heart disease, Sydenham chorea, and other autoimmune sequelae is related to autoantibodies that are characteristic of autoimmune diseases and result from the immune responses against the group A streptococcal infection by the host. The streptococcal immune mediated sequelae, including acute rheumatic fever, are due to antibody and cellular immune responses that target antigens in the heart and brain as well as the group A streptococcal cross-reactive antigens as reviewed below in this chapter. The group A streptococcus is associated with a group of diseases affecting the heart, brain, and joints and are collectively referred to as acute rheumatic fever.
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