Type III hypersensitivity reactions Notes
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This Osmosis High-Yield Note provides an overview of Type III 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 III hypersensitivity reactions:
NOTES NOTES TYPE III HYPERSENSITIVITY REACTIONS GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Hypersensitivity reaction mediated by immune complexes ▫ Antibodies (IgG) binding to soluble antigens → antigens not bound to cell surfaces ▪ Formation of immune complexes → complement activation (esp. C3a, C4a, C5a) ▫ Anaphylatoxins → increase vascular permeability → edema ▫ Chemokins → recruitment of phagocytes, neutrophils, mast cells → degranulation of lysosomal enzymes, reactive oxygen species → inﬂammation, tissue necrosis (ﬁbrinoid necrosis) ▫ May also elicit systemic inﬂammation ▪ Common sites of immune complex accumulation ▫ Blood vessel walls → vasculitis ▫ Kidneys → glomerulonephritis ▫ Joints → arthritis ▪ If triggered by single exposure to antigen, resolves after catabolism of immune complexes → acute serum sickness ▪ If repeated/prolonged exposure → chronic serum sickness ▫ Systemic erythematosus lupus (SLE), polyarteritis nodosa, poststreptococcal glomerulonephritis, reactive arthritis Common Type III hypersensitivity reactions ▪ Henoch–Schönlein purpura ▪ Hypersensitivity vasculitis ▪ Reactive arthritis ▪ Farmer’s lung ▪ Post-streptococcal glomerulonephritis ▪ Serum sickness ▪ Arthus reaction 226 OSMOSIS.ORG ▪ Systemic lupus erythematosus ▪ Subacute bacterial endocarditis ▪ Rheumatoid arthritis SIGNS & SYMPTOMS ▪ ▪ ▪ ▪ ▪ ▪ Fever, fatigue, weight loss Skin: rash, urticaria Kidney: proteinuria Joints: arthralgias Mucosa: ulcers Serosa: pleuritis, pericarditis DIAGNOSIS LAB RESULTS ▪ Antibody testing ▪ Histopathology to observe ﬁbrinoid necrosis ▫ Necrosis of vessel wall with inﬁltration of neutrophils, eosinophils, complement, plasma proteins; staining pattern reminiscent of ﬁbrin Figure 38.1 A vessel displaying ﬁbrinoid necrosis in Churg–Strauss syndrome, which is a type III hypersensitivity reaction.
Chapter 38 Type III Hypersensitivity Reactions ▪ Immunoﬂuorescence microscopy to visualize immune complexes ▪ Complement levels in blood ▫ Track disease progression TREATMENT MEDICATIONS ▪ SLE ▫ Administration of anti-inﬂammatory, corticosteroids, cytotoxic medications to decrease inﬂammatory activity SERUM SICKNESS osms.it/serum-sickness PATHOLOGY & CAUSES ▪ Systemic Type III hypersensitivity reaction against foreign antibodies in serum ▪ Exposure to foreign serum → triggers B cells to become plasma cells, produce IgG antibodies against foreign antibodies → immune complexes formed, deposited in basement membrane → complement activation, immune cells recruitment → lysosomal enzymes, reactive oxygen species, cytokines produced → local, systemic inﬂammatory response ▪ Initial exposure ▫ 4–10 days to develop reaction ▪ Second exposure ▫ Faster, more potent reaction ▪ Resolves after withdrawal of culprit agent CAUSES ▪ Medications (e.g. cefaclor, anti-seizure medications); infections (e.g., hepatitis B); vaccines SIGNS & SYMPTOMS ▪ Allergy-like response ▪ Present within 1–2 weeks if initial exposure, 12–36 hours if second exposure ▫ General malaise, erythema, itching, arthralgia ▪ Fever > 38.5°C/101.3°F, rash, lymphadenopathy, polyarthritis, proteinuria DIAGNOSIS LAB RESULTS ▪ Complete blood count (CBC) ▫ Neutropenia, increase in lymphocytes ▪ Elevation of erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) ▪ Urinalysis ▫ Mild proteinuria (50%) OTHER DIAGNOSTICS ▪ Clinical presentation; suspected when allergy-like symptoms present after administration of potential responsible agent (e.g. antivenom serum after bitten by snake) ▪ Testing to exclude infections (e.g. hepatitis B) TREATMENT MEDICATIONS ▪ Relieve symptoms with antihistamines, analgesics ▪ Glucocorticoids for individuals with severe clinical features (e.g. very high fever, severe arthritis, extensive rashes) OTHER INTERVENTIONS ▪ Discontinue, avoid offending agent OSMOSIS.ORG 227
Osmosis High-Yield Notes
This Osmosis High-Yield Note provides an overview of Type III 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 III hypersensitivity reactions by visiting the associated Learn Page.