PD research using ApoE mice has also linked increased levels of ApoE to higher neuronal stress and activation of microglia, triggering the release of the cytokine interferon-γ (IF-γ) and upregulation of neuronal major histocompatibility complex class I (MHC-I) levels [192], which has the effect of making the neurons more easily recognised and destroyed by T cells [192,194,195]. The gene discussed is APOE; the disease is Parkinson disease.