# Transplant Pathology Basics

> Transplant basics for MBBS Pathology: graft types, HLA matching, crossmatch, calcineurin inhibitors, CMV and PTLD, with THOA and NOTTO facts for Indian exams.

- Canonical URL: https://prepelephant.com/topics/mbbs/pathology/transplant-pathology-basics
- Exam / course: MBBS · 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 Basics", PrepElephant, https://prepelephant.com/topics/mbbs/pathology/transplant-pathology-basics

## Direct answer

Transplant vocabulary is graded by genetic distance: an autograft moves tissue within the same person, an isograft (syngeneic graft) between identical twins, an allograft between genetically different members of the same species, and a xenograft across species. Allograft survival rests on three pillars — ABO compatibility, HLA matching with a negative pretransplant crossmatch, and lifelong combination immunosuppression, classically a calcineurin inhibitor, an antiproliferative agent and a steroid. Rejection itself — hyperacute, acute cellular, antibody-mediated, chronic — has its own page; the basics here are matching, the drugs, and the infection and malignancy complications of immunosuppression.

## What you must remember

- **HLA matching for the kidney:** donor and recipient are matched at HLA-A, HLA-B and HLA-DR, and a mismatch at DR carries the strongest penalty for graft survival — the order to quote is DR, then B, then A.
- **The crossmatch:** recipient serum tested against donor lymphocytes; a positive crossmatch predicts hyperacute rejection and contraindicates transplantation. Panel-reactive antibody (PRA) levels quantify prior sensitisation.
- **Allorecognition:** direct pathway — recipient T cells recognise intact donor MHC on donor antigen-presenting cells (dominant in early acute rejection); indirect pathway — donor peptides presented on recipient MHC (dominant in chronic rejection).
- **Calcineurin inhibitors:** ciclosporin binds cyclophilin and tacrolimus binds FKBP-12; either complex inhibits calcineurin, so NFAT is not dephosphorylated and IL-2 transcription falls. Both are nephrotoxic; ciclosporin adds gingival hyperplasia, hirsutism and hyperuricaemia, tacrolimus adds neurotoxicity and diabetes.
- **Antiproliferatives and mTOR:** mycophenolate inhibits IMPDH (lymphocyte-restricted purine synthesis); azathioprine causes marrow suppression, dangerously compounded by allopurinol, which blocks its clearance; sirolimus impairs wound healing, so it is avoided in the immediate postoperative period.
- **The infection calendar:** first month — technical and donor-derived infections; months one to six — the opportunistic window of cytomegalovirus (highest risk in donor-positive, recipient-negative pairs), BK virus nephropathy and Pneumocystis, for which co-trimoxazole prophylaxis is routine; beyond six months — community infections, chronic viral disease and PTLD.
- **PTLD:** EBV-driven B-cell proliferation, commonest in children and after T-cell-depleting induction, ranging from polyclonal hyperplasia to frank lymphoma; first move is reduction of immunosuppression, with rituximab for established disease.
- **Indian framework:** the Transplantation of Human Organs Act 1994 (amended 2011) regulates donation and defines near-relatives for living donation; NOTTO — the National Organ and Tissue Transplant Organisation — maintains the national registry, with ROTTOs and SOTTOs beneath it.
- **Immune privilege:** the cornea, being avascular, is transplanted without HLA matching or systemic immunosuppression in most cases.

## The first year after a kidney transplant

Before surgery come the immunological gates: blood group compatibility, HLA typing at A, B and DR, antibody screening with PRA, and a final crossmatch — a positive result stops the operation. Induction at the time of transplant adds steroid with, in sensitised recipients, antithymocyte globulin or the anti-CD25 antibody basiliximab.

Maintenance settles into the standard triple regimen, monitored by tacrolimus trough levels, because under-dosing invites rejection and over-dosing invites nephrotoxicity, infection and malignancy. The first month is watched for surgical and donor-derived problems — urine leak, vascular thrombosis, transmitted infection. Months two to six are the opportunist window: a febrile patient with leucopenia and a rising creatinine gets CMV PCR (donor-positive, recipient-negative pairs carry the highest risk, and valganciclovir prophylaxis or pre-emptive therapy follows), while BK viraemia is checked when the creatinine creeps without rejection on biopsy. From six months onward the agenda becomes chronic — donor-specific antibody surveillance, chronic rejection, skin and cervical cancer screening, and vigilance for PTLD in any recipient with fever, lymphadenopathy and weight loss.

## The classic viva trap

Drug adverse-effect profiles are asked as single best answers, and the trap is the gouty transplant patient: starting allopurinol in someone on azathioprine blocks xanthine oxidase, slows 6-mercaptopurine clearance and produces precipitous pancytopenia — the pair must not be combined without a major dose reduction or a switch to mycophenolate. The second trap is giving sirolimus early, when its anti-proliferative effect on fibroblasts breaks down wound and anastomotic healing; it is introduced later, or not at all. Third, the cornea accepts the exception — no systemic immunosuppression for most corneal grafts, because an avascular bed denies immune access.

## Frequently asked questions

### Which HLA locus most strongly influences kidney graft survival?

HLA-DR, followed by HLA-B and then HLA-A — matching priority is quoted in that order.

### What is the difference between an autograft, isograft and allograft?

Autograft is within the same individual, isograft between identical twins (syngeneic), and allograft between genetically different members of the same species; xenografts cross species.

### How do calcineurin inhibitors suppress the immune response?

Ciclosporin-cyclophilin or tacrolimus-FKBP complexes inhibit calcineurin, preventing NFAT dephosphorylation and shutting down IL-2 transcription, the key T-cell growth signal.

### Which infections dominate the first to sixth month after transplant?

Opportunists, chiefly cytomegalovirus, plus BK virus and Pneumocystis jirovecii — the last prevented by routine co-trimoxazole prophylaxis.

### Which Indian law and organisation regulate organ transplantation?

The Transplantation of Human Organs Act 1994, amended in 2011, and NOTTO — the National Organ and Tissue Transplant Organisation — which coordinates with regional and state organisations.