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 1 Expression

Where are HLA Class I molecules expressed?

HLA Class 1 molecules are expressed on all nucleated cells and include HLA-A, HLA-B, and HLA-C, where they present endogenous antigens to CD8⁺ cytotoxic T cells.

HLA Class II Expression

Where are HLA Class II molecules expressed?

HLA Class II molecules are expressed only on antigen-presenting cells (APCs) and include HLA-DR, HLA-DQ, and HLA-DP, where they present exogenous antigens to CD4⁺ helper T cells.

HLA Polymorphism

What does it mean that HLA genes are highly polymorphic?

HLA genes are described as highly polymorphic because thousands of different alleles exist within the population, which enhances overall immune defence but also makes finding a perfect transplant match difficult.

HLA Haplotype Inheritance

Front: What is HLA haplotype inheritance?

HLA genes are inherited together as a haplotype on chromosome 6, with one haplotype passed down from each parent, which means siblings have a 25% chance of being a complete 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?

Chronic rejection occurs months to years after transplantation and is caused by long-term immune-mediated injury, leading to progressive fibrosis and vascular narrowing that results in 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. The donor and the recipient are HLA-incompatible

3. The 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