Immunology - Type III Hypersensitivity (Serum Sickness)

Question 1

General

Answer 1

typically happens when a patient receives foreign serum and elicits an antibody response against those foreign antigens

Question 2

Mechanism (snake bite)

Answer 2

get bitten by a snake -> get serum with anti-venom antibodies -> antibodies against the anti-venom antibodies -> if the person gets bitten by a snake again and gets serum with anti-venom antibodies again those antibodies that were made the first time around will make immune complexes with the anti-venom antibodies which are treated like an antigen -> vasculitis and tissue necrosis

Question 3

Pathology

Answer 3

Systemic type III hypersensitivity reaction against foreign antibodies in serum, exposure to foreign serum -> B cells become plasma cells that produce IgG antibodies -> immune complexes formed and deposited in basement membrane -> complement activation and immune cells recruitment -> lysosomal enzymes + reactive oxygen species + cytokines produced -> local systemic inflammatory response, resolves after withdrawal of culprit agent

Question 4

Initial vs second exposure

Answer 4

4-10 days to develop reaction vs faster more potent reaction

Question 5

causes

Answer 5

medications (ie cefaclor, anti-seizure medications), infections (ie hep B), vaccines

Question 6

signs and symptoms

Answer 6

allergy-like response, present within 1-2 weeks if initial exposure, 12-36 if second exposure, general malaise, erythema, itching, arthralgia, fever >38.5ºC, rash, lymphadenopathy, polyarthritis, proteinuria

Question 7

diagnosis

Answer 7

complete blood count (CBC, neutropenia + increase in lymphocytes), elevation of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), urinalysis (mild proteinuria (50%), clinical presentation (suspected when allergy-like symptoms present after administration of potential responsible agent (ie antivenom serum after bitten by snake)), testing to exclude infections (ie hep B)

Question 8

treatment

Answer 8

relieve symptoms with antihistamines and analgesics, glucocorticoids for individuals with severe clinical features (ie very high fever severe arthritis, extensive rashes), discontinue + avoid offending agent