Transplant Rejection Reactions

Hyperacute rejection

an antibody-mediated reaction (type II hypersensitivity) caused by preformed IgG antibodies within the recipient that are directed against donor antigens and trigger complement activation.

(do not mistake as type I, IgE mediated anaphylaxis due to its very rapid onset)

Acute rejection

• Most common,
• Type IV hypersensitivity,
• From weeks to months

Acute cellular rejection is triggered when lymphocytes that have been activated against donor antigens are present. They are primarily activated in the lymphoid tissues of the recipient. Donor dendritic cells, which are also known as passenger leukocytes, enter the recipient's circulation and function as antigen-presenting cells, migrating to lymphoid tissues. Low levels of antibodies may also be responsible for acute rejection, because at a low level, they avoid triggering the complement system and precipitating hyperacute rejection.

Chronic Rejection

takes months to years

S/S - worsening HTN and slowly progressive rise in serum Creatinine

Chronic, indirect immune response against donor alloantigens --> obliterative fibrous intimal thickening and scattered mononuclear infiltration of the surrounding tissues.

Consequent renal ischemia and chronic inflammatin cause shrinking of the renal parenchyma with tubular atrophy and interstitial fibrosis.

Graft vs. Host

GVHD (type IV hypersensitivity)

as the name implied, Donor (Graft) T cell sensitize against Host MHC antigens