Type II hypersensitivity reactions Notes
Osmosis High-Yield Notes
This Osmosis High-Yield Note provides an overview of Type II hypersensitivity reactions essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Type II hypersensitivity reactions:
NOTES NOTES TYPE II HYPERSENSITIVITY REACTIONS GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Antibody-mediated hypersensitivity reactions; tissue-speciﬁc, broad spectrum of disease manifestations ▪ Disorder due to self-reactive B cells that produce antibodies (e.g. IgM, IgG) that bind antigens on host cells, form antigenantibody complex at tissue site ▫ Defective central tolerance → autoantibodies against self/intrinsic antigens ▫ Embedded outside/extrinsic antigens into normal cell surface alter cell antigenicity Common Type II hypersensitivity reactions ▪ Hemolytic disease of the newborn ▪ Autoimmune hemolytic anemia ▪ Immune thrombocytopenic purpura ▪ Bullous pemphigoid ▪ Pemphigus vulgaris ▪ Rheumatic fever ▪ Goodpasture syndrome ▪ Guillain–Barré syndrome ▪ Graves’ disease ▪ Myasthenia gravis ▪ Pernicious anemia TYPES ▪ Four pathologic mechanisms Activation of complement system ▪ IgM/IgG antibody binds ﬁxed antigen on cell → C1 binds Fc portion of IgM/IgG → classical pathway C2–C9 cleavage/ activation → C3a–C5a anaphylatoxin production ▫ Chemoattract promote degranulation of neutrophils, basophils, mast cells (granules of lysosomal contents of leukocytes fuse, degrade target cell → cell death; mast cell degranulation contents include histamine → promote further immune cell response) ▫ Promote macrophage, monocytes pro-inﬂammatory cytokine release; interleukin (IL1), 6 (e.g. Goodpasture’s syndrome, antibodies against Type IV collagen in lung, kidney) ▪ Membrane attack complex (MAC) formation (C5b–C9) → insertion into, disruption of cell membrane → impaired osmotic gradient → cell lysis (e.g. ABO mismatch in transfusion reaction, hyperacute transplantation reaction) Opsonization, phagocytosis ▪ Antigen-opsonin C3b/IgG complex circulate ▫ To spleen → ﬁxed macrophages recognize IgG-bound antigens → phagocytosis ▫ To liver → Kupffer cells recognize C3b-bound antigens → phagocytosis (Autoimmune hemolytic anemia (AIHA), ABO, Rh-hemolytic disease of newborn) Antibody-dependent cell-mediated cytotoxicity (ADCC) ▪ Natural killer cells bind Fc portion of antibody-antigen complex → release perforins, granzymes, granulysin → apoptotic cell death Antibody-mediated cellular dysfunction (only non-cytotoxic mechanism) ▪ Physical presence of antibody at receptor binding site impairs physiologic function ▫ Activate: thyroid hormone receptor in Graves’ disease ▫ Inhibit: acetylcholine receptor in Myasthenia gravis (MG) OSMOSIS.ORG 223
SIGNS & SYMPTOMS ▪ Acute hemolytic transfusion reactions ▫ Fevers, chills; nausea/vomiting; ﬂank, chest pain; dyspnea ▪ Autoimmune hemolytic anemia ▫ Fatigue, jaundice, hepatosplenomegaly (HSM) ▪ Bullous pemphigoid ▫ Abdominal, groin, extremity blistering ▪ Erythroblastosis fetalis ▫ Kernicterus, death in fetus ▪ Goodpasture syndrome ▫ Dyspnea, hemoptysis, hematuria ▪ Graves’ disease ▫ Tremor, insomnia, irritability, weight loss, tachycardia ▪ Guillain–Barre syndrome ▫ Ascending paralysis ▪ Idiopathic thrombocytopenic purpura ▫ Petechiae, skin ecchymoses ▪ Myasthenia gravis ▫ Weakness, ptosis, diplopia, dysphagia ▪ Pemphigus vulgaris ▫ Blistering of oral mucosa ▪ Pernicious anemia ▫ Fatigue, glossitis, B12 deﬁciency sequelae ▪ Rheumatic fever ▫ Migratory polyarthritis, fever, +/- cardiac involvement 224 OSMOSIS.ORG DIAGNOSIS LAB RESULTS ▪ Coombs testing ▫ Direct: detects Fc region of bound antibodies on red blood cells (RBCs) (e.g. ABO incompatibility) ▫ Indirect: detects circulating serum antibodies against known antigen (e.g. anti-D) ▪ RBC antigen testing ▪ Immunohistochemistry (IHC) ▪ Diffuse radioactive iodine (RAI) uptake OTHER DIAGNOSTICS ▪ Clinical presentation of disease-speciﬁc symptoms TREATMENT MEDICATIONS ▪ Corticosteroids ▪ Severe reactions may require plasmapheresis/immunosuppressants
Chapter 37 Type II Hypersensitivity Reactions OSMOSIS.ORG 225
Osmosis High-Yield Notes
This Osmosis High-Yield Note provides an overview of Type II hypersensitivity reactions essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Type II hypersensitivity reactions by visiting the associated Learn Page.