50 c. Describe in detail one mechanism that is not based on pathogen antigen-specificity (i.e., bystander activation) (4p) 

  • Chronic infection ! long term inflammation leads to tissue damage and enhanced MHC-class II expression on non-phagocytic cells (due to high concentrations of INF-γ) which in combination favor presentation of autoantigens. Autoreactive T cells that have escaped from negative selection in the thymus can become activated under these conditions. Bystander activation of autoreactive T cells ! In a strong inflammatory environment (because of an immune response to any antigen) Regulatory T cells that usually prevent activation of may become “overruled” and subsequent activation of autoreactive T cells may occur. 

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