Overview
Renal transplant rejection describes immune-mediated inflammation in a transplanted kidney due to the recipient’s immune system recognising the graft as non-self. It can be divided into different types based on the immunological mechanism:
- Hyperacute rejection (within minutes to hours)
- Acute graft failure (<6 months)
- Chronic graft failure (>6 months)
HLA, MHC, and matching
Renal transplant matching is done using the human leukocyte antigen (HLA) system (also known as major histocompatibility complex, MHC), which is encoded on chromosome 6. There are two classes of HLA (MHC), both with different roles and antigens:
- HLA (MHC) class I – has -A, -B, and -C antigens
- HLA (MHC) class II – has -DR, -DP, and -DQ antigens
When matching for renal transplants, the HLA-DR antigens are most important, followed by HLA-B, and HLA-A.
Types of Renal Transplant Rejection
Hyperacute rejection
Hyperacute rejection occurs due to pre-existing antibodies in the recipient’s blood against the donor antigen (usually ABO blood group or HLA antigens). This leads to a type II hypersensitivity reaction causing polymorphonuclear cell infiltration, thrombosis, and necrosis of renal tissue.
Hyperacute rejection generally happens within minutes to hours following the transplant and no treatment is possible. The graft must be removed.
Acute graft failure
Acute graft failure occurs within 6 months of the transplant and describes T-cell mediated rejection of the graft.
It is usually asymptomatic and characterised by:
- Deranged urea and electrolytes
- Proteinuria
- Pyuria – white cells present in the urine
Acute graft failure may be reversible with immunosuppressants.
Chronic graft failure
Chronic graft failure may occur due to both immune and non-immune-mediated factors. Causes include:
- Non-compliance with immunosuppressive medication
- Recurrence of the original disease (e.g. IgA nephropathy and focal segmental glomerulosclerosis)
