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NBME 21 Answers

nbme21/Block 4/Question#24

A 56-year-old man undergoes a renal transplant. ...

IgG plus complement

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 +2  upvote downvote
submitted by hayayah(508),

Hyperacute transplant rejection occurs within minutes d/t pre-existing recipient antibodies that react to donor antigen (type II hypersensitivity reaction), activate complement.

mcl  [Useful figures illustrating transplant rejection](https://www.stomponstep1.com/transplant-rejection-hyperacute-acute-chronic-graft-versus-host/) +  




 +0  upvote downvote
submitted by priapism(3),

Per First Aid: antibodies against ABO blood types tend to be IgM or IgG, which is why the answer is IgG + complement and not IgA + complement

yotsubato  IgA also has no role in any hypersensitivity reaction +2  
divya  hi. where is this given in first aid? +  




 +0  upvote downvote
submitted by h0odtime(3),

Transplant Rejections (p.119)

  • Hyperacute - Minutes pre-existing Ab attack new organ Ag + activate complement T2
  • Acute - Weeks CD8 +/- CD4 bind organ MHC. T4
  • Chronic - Months/years CD4s can activate macrophages and mediate damage T4, or activate B cells --> Ab --> damage graft. T2 or T4
  • GVH - Time varies, organ with T-cells grow and reject foreign host. T4

Transplant Types

  • Autologous Self skin grafts
  • Allogenic Normal organ transplant
  • syngeneic graft (isograft) Monozygotic twins
  • xenograft animal to human heart valves

ABCD Hypersensitivity (p.112 FA2020)

  • T1 : Anaphylactic & Atopic
  • T2: (anti)Body-mediated
  • T3: Complex (Immune)
  • T4: Delayed Cell Mediated