# Transplant Pathology Overview

> FMGE Pathology notes on transplant pathology: hyperacute, acute cellular and antibody-mediated rejection, Banff grading, C4d, GVHD and PTLD.

- Canonical URL: https://prepelephant.com/topics/fmge/pathology/transplant-pathology-overview
- Exam / course: FMGE · Subject: Pathology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Transplant Pathology Overview", PrepElephant, https://prepelephant.com/topics/fmge/pathology/transplant-pathology-overview

## Direct answer

Transplant pathology reads allograft injury by time and mechanism: hyperacute rejection, within minutes to hours, is complement-mediated thrombosis of graft vessels by preformed anti-donor antibodies (ABO or HLA), and the graft is lost; acute cellular rejection, days to months later, is T-cell mediated — tubulitis and interstitial lymphocytes in kidney allografts, graded by the Banff system; antibody-mediated rejection shows microvascular inflammation with C4d deposition in peritubular capillaries; and chronic rejection, months to years, is fibrointimal thickening of arteries with interstitial fibrosis and tubular atrophy. Around the graft sit the complications of immunosuppression itself — CMV and BK virus infection, post-transplant lymphoproliferative disorder — and graft-versus-host disease when donor immune cells attack the host.

## What you must remember

- **Time-map:** hyperacute (minutes-hours, antibody, thrombosed vessels, fibrinoid necrosis), acute cellular (days-months, T cells), chronic (months-years, arteriopathy and fibrosis) — time is the first diagnostic clue in any vignette.
- **Prevention of hyperacute rejection:** ABO matching and a negative lymphocytotoxic crossmatch; HLA-DR matching carries the strongest graft-survival weight for kidneys.
- **Acute cellular rejection histology:** interstitial oedema with lymphocytes plus tubulitis (lymphocytes breaching tubular basement membranes); treated with pulse steroids, antithymocyte globulin for steroid-resistant cases.
- **Antibody-mediated rejection:** donor-specific antibodies, microvascular inflammation (glomerulitis, peritubular capillaritis) and C4d staining in peritubular capillaries — the complement split product that marks antibody injury.
- **Chronic rejection:** transplant arteriosclerosis of large vessels with diffuse intimal fibrosis and, in kidneys, interstitial fibrosis with tubular atrophy; largely irreversible.
- **Graft-versus-host disease:** donor T cells attack host skin, gut and liver — basal keratinocyte apoptosis with satellite lymphocytes in skin, crypt apoptosis in gut, bile duct injury in liver.
- **Immunosuppression complications:** CMV (owl-eye inclusions, typically the first three months), BK polyomavirus nephropathy (SV40-positive tubulointerstitial nephritis mimicking rejection), and EBV-driven post-transplant lymphoproliferative disorder, treated first by reducing immunosuppression.

## A creatinine that rose at month three

A renal transplant recipient's creatinine climbs at three months. The differential walks a fixed ladder: rejection (cellular or antibody-mediated), calcineurin-inhibitor toxicity (isometric tubular vacuolisation, arteriolar hyalinosis), BK virus nephropathy, obstruction, and recurrence of the original disease. A biopsy read with Banff criteria scores interstitial inflammation, tubulitis and vascular changes; if C4d lights up the peritubular capillaries and donor-specific antibodies circulate, antibody-mediated rejection brings plasmapheresis and rituximab into the conversation. If instead tubular epithelial nuclei show viral inclusion changes confirmed by SV40 immunostain, the diagnosis is BK nephropathy and reducing, not escalating, immunosuppression is the move — the therapeutic mirror-image that makes this biopsy worth performing before treating.

## Where students slip

C4d is quoted without meaning: it is a complement degradation product whose deposition in peritubular capillaries fingerprints classical-pathway antibody injury. Candidates swap the histologies — tubulitis belongs to acute cellular rejection, arterial fibrinoid necrosis to severe vascular rejection, and isometric vacuolisation to calcineurin-inhibitor toxicity. GVHD's skin finding is mislabelled as interface dermatitis generically; the specific phrase is basal keratinocyte apoptosis with satellite lymphocytes. Finally, PTLD is remembered as lymphoma to be treated with chemotherapy first, when the first step in many cases is reduction of immunosuppression, because the driver is EBV-infected B cells outgrowing a suppressed host.

## Frequently asked questions

### What causes hyperacute rejection?

Preformed anti-donor antibodies (ABO or HLA) binding graft endothelium, activating complement and causing platelet-fibrin thrombi and graft loss within minutes to hours.

### What does C4d positivity in a graft biopsy indicate?

Complement activation by donor-specific antibodies — the immunohistochemical signature of antibody-mediated rejection, especially in peritubular capillaries.

### What is the Banff system?

A standardised schema for scoring renal allograft biopsy features — interstitial inflammation, tubulitis, vascular changes and fibrosis — that converts morphology into treatment grades.

### What is the hallmark skin lesion of GVHD?

Basal keratinocyte apoptosis with satellite lymphocytes, accompanied by gut crypt apoptosis and bile duct injury.

### What drives post-transplant lymphoproliferative disorder?

EBV-driven B-cell proliferation in an immunosuppressed host, managed first by reducing immunosuppression, with rituximab-based therapy for progressive disease.