A number of experiments have suggested that there is an antigenic relationship between the HLA complex and streptococcal bacterial structures. Using inhibition of cytotoxicity of HLA antisera as our assay system, it was demonstrated that the inhibitory effect on HLA cytotoxicity by streptococcal antigens is, in reality, due to activation and consumption of components of the alternate complement pathway. In addition, antisera prepared against streptococcal membrane antigens had no cytotoxic effect on a large panel of human lymphocytes, nor did these antisera exhibit immunofluorescent staining of lymphocytes directly. These experiments are compatible with our concept that the HLA complex may have evolved through selective evolutionary pressure as a means of escaping bacterial mimicry.

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