Type III hypersensitivity (mechanism of disease) with examples

This is a flowchart for Type III hypersensitivity, covering the etiology, pathophysiology, and manifestations with examples.
ADDITIONAL TAGS:
Tetanus or diphtheria vaccine are the Ag → Arthus reaction
Genetics → farmers → bird droppings, spores (from HVAC, moldy hay, sugar cane cheese casings, paints, compost), sawdust microbes, chemicals (isocyanates) form Ag → Hypersensitivity pneumonitis
Remission and relapse affecting any organ, most commonly arthritis, malar rash, Raynaud phenomenon, fever, fatigue, pleuritis / pericarditis → pleuritic sharp chest pain, friction rub, seizures, psychosis
Risk factors / SDOH
Cell / tissue damage
Vascular / flow physiology
Type III hypersensitivity
Medicine / iatrogenic
Infectious / microbial
Environment / toxins
Immunology / inflammation
Signs / symptoms
Disease / condition / results
Diet / nutrition
Genetics / hereditary
Neoplasm / cancer
Pathophysiology
Etiology
Manifestations
Inflammation
Complexes deposited in tissues (blood vessels, joints, glomerular basement membranes, etc)
Formation of immune complex (Ag-Ab complex)
IgG in
circulation
Soluble antigen in circulation
Initiates complement cascade
Chemotaxis of neutrophils
IgG binds to Fc receptor on neutrophils, releasing lysosomal enzymes
Damages local tissue
Cell death
Systemic lupus erythematosus
+/- lupus nephritis
+/- thrombosis
Joint pain, swelling, synovial destruction, deformities, morning stiffness (MCP and PIP joints); rheumatoid nodules pulmonary fibrosis=dyspnea, dry cough, fatigue, inspiratory crackles; AAS= neck pain, cervical radiculopathy, spinal cord compression; Felty = arthritis, splenomegaly, and neutropenia
Rheumatoid arthritis
+/- pulmonary fibrosis
+/- atlantoaxial subluxation
+/- Felty syndrome
Nephritic syndrome: hematuria (tea- or cola-colored urine), mild proteinuria, edema, hypertension
Group A strep tonsillopharyngitis
or skin infections →
Poststreptococcal glomerulonephritis
Asymptomatic OR Recurring episodes of gross hematuria, flank pain, low fever; +/- nephritic syndrome
Mucosal (respiratory or GI) infections
→ IgA immune complexes deposit in kidney → IgA nephropathy
Polyarteritis nodosa
Systemic vasculitis of medium-sized vessels
Fever, weight loss, muscle / joint pain; AKI → hypertension, MI → chest pain, sweating, skin → rash, ulcers, nodules, neuro → stroke, polyneuropathy, GI → abd pain, melena, nausea, vomiting. Spares the lung (vs other vasculitides)
Tender, symmetrical palpable purpura on the lower limbs; +/- subcutaneous nodules, urticaria, ulcers, vesicles; +/- arthralgias
Viral (HIV, HCV), drugs (propylthiouracil, hydralazine, allopurinol) form Ag → Cutaneous small-vessel vasculitis, aka drug-induced or hypersensitivity vasculitis
Acute: fever, flu-like headache, bodyache, malaise, fine crackles
Subacute: insidious cough, dyspnea, fatigue over weeks to months
Chronic: progressive dyspnea, weight loss, cough, fatigue, cyanosis, rales
Antitoxin, antivenom, allopurinol, antibiotics, or Hep B, rabies are the Ag →
Serum sickness and SS-like reaction
Fever, rash, arthralgias occuring 1-3 weeks after exposure; +/- lymphadenopathy, +/- headache, +/- blurred vision, +/- abdominal pain/nausea/vomiting/diarrhea, +/- edema
Similar to cutaneous small-vessel vasculitis; : swelling, erythema, hemorrhage; +/- superficial skin necrosis after booster vaccination