Transplantation & HLA Perfect Exam-Ready Flashcards (16)

MHC vs HLA

What is the difference between MHC and HLA?

• MHC (Major Histocompatibility Complex): General term used across species

• HLA (Human Leukocyte Antigen): The human version of MHC

• Function: Present antigens to T cells and distinguish self from non-self

HLA Class I Expression

Where are HLA Class I molecules expressed?

• On all nucleated cells

• Includes HLA-A, HLA-B, HLA-C

• Present endogenous antigens to CD8⁺ cytotoxic T cells

HLA Class II Expression

Where are HLA Class II molecules expressed?

• Only on antigen-presenting cells (APCs)

• Includes HLA-DR, HLA-DQ, HLA-DP

• Present exogenous antigens to CD4⁺ helper T cells

HLA Polymorphism

What does it mean that HLA genes are highly polymorphic?

• Thousands of different alleles exist in the population

• Improves population immune defense

• Makes finding a perfect transplant match difficult

HLA Haplotype Inheritance

Front: What is HLA haplotype inheritance?

• HLA genes are inherited together as a block on chromosome 6

• One haplotype from each parent

• Siblings have a 25% chance of being a full HLA match

Autograft vs Allograft

What is the difference between an autograft and an allograft?

 

• Autograft: Tissue transplanted within the same individual → no rejection

• Allograft: Tissue transplanted between genetically different individuals → risk of rejection

Hyperacute Rejection

What is hyperacute rejection?

• Occurs minutes to hours after transplantation

• Caused by pre-existing antibodies (anti-HLA or anti-ABO)

• Leads to immediate graft thrombosis and failure

• Transplant must be stopped

Acute Rejection

Front: What is acute rejection?

• Occurs days to weeks post-transplant

• Mainly T-cell mediated

• Recipient T cells recognise donor HLA as foreign

• Often reversible with immunosuppression

Chronic Rejection

Front: What is chronic rejection?

• Occurs months to years after transplantation

• Caused by long-term immune injury

• Progressive fibrosis and vascular narrowing

• Leads to gradual graft failure

Crossmatch Test

Front: What is the crossmatch test?

• Final compatibility test before transplant

• Recipient serum mixed with donor lymphocytes

• Cell death = positive crossmatch = incompatible transplant

Purpose of HLA Typing

Why is HLA typing performed?

• Identifies donor and recipient HLA alleles

• Improves graft survival

• Reduces rejection risk

• Minimises immunosuppression requirements

Graft-Versus-Host Disease (GVHD)

Front: What is graft-versus-host disease?

• Donor T cells attack recipient tissues

• Occurs mainly in bone marrow / HSCT

• Potentially fatal complication

Requirements for GVHD

Front: What three conditions are required for GVHD?

1. Graft contains immunocompetent T cells

2. Donor and recipient are HLA-incompatible

3. Recipient is immunocompromised

Target Organs in Acute GVHD

Front: What organs are primarily affected in acute GVHD?

• Skin: Rash

• Liver: Jaundice

• GI tract: Severe diarrhoea

 Transfusion-Associated GVHD (TA-GVHD)

Front: How is transfusion-associated GVHD prevented?

• By irradiating blood products

• Destroys donor T-cell DNA

• Prevents T-cell proliferation in the recipient

Panel Reactive Antibody (PRA)

Front: What is Panel Reactive Antibody (PRA)?

• Measures the percentage of HLA antibodies in a patient

• High PRA = highly sensitised patient

• Makes finding a compatible donor difficult