Q.Mention the symptoms of allograft rejection in the host.

Allograft rejection is the host's cell-mediated and humoral immune attack on a transplanted organ/tissue from a genetically non-identical donor, and it manifests as a mix of systemic and graft-site signs depending on how quickly it occurs.

Why rejection happens: an allograft carries donor MHC (HLA) molecules that differ from the recipient's own, so the host's T lymphocytes recognise them as foreign antigens. This activates cytotoxic T cells that directly destroy graft cells, and helper T cells that recruit macrophages and stimulate B cells to make anti-donor antibodies, together damaging the grafted tissue's blood vessels and cells.

Symptoms/signs of allograft rejection in the host:

• Systemic: fever, chills, general malaise/fatigue, loss of appetite.
• Local (graft site): pain, tenderness, swelling and induration (hardening) at the transplant site.
• Organ dysfunction: for a transplanted kidney - reduced urine output, rising blood urea and creatinine, hypertension and fluid retention; for a transplanted liver - deranged liver function tests and jaundice; similar functional decline is seen in any rejected organ.
• Skin/graft appearance: in a rejected skin graft, the tissue becomes oedematous and progressively dark/discoloured, later necrosing and sloughing away from the recipient bed.
• Histological findings on biopsy: dense infiltration of lymphocytes and macrophages into the graft, damage to small blood vessels (vasculitis), and tissue necrosis.

Types of rejection (by time course):

• Hyperacute rejection - occurs within minutes to hours, caused by pre-formed antibodies in the recipient against donor antigens. …