hypersensitivity reaction disease hypersensitivity reaction type II disease An immune system disease that is an overactive immune response of the body against substances and tissues normally present in the body resulting from an abnormal functioning of the immune system that results in the production of antibodies or T cell directed against the host tissues. DOID:417 ICD9CM:720 UMLS_CUI:C0003089 Xref MGI. autoimmune disease disease_ontology OMIM:109100