A corticosteroid is a glucocorticoid-based medication that works principally to block T cell and APC derived cytokine and cytokine-receptor expression. The major elements blocked are IL-1 and IL-6. Secondary effects of corticosteriods include the blocking of IL-2, INF-gamma, and TNF-alpha. These elements, notably IL-1, are essential for lymphocyte-APC communication- a decrease in production effectively obstructs an APC's capacity to activate allograft-specific lymphocytes. As a result, threat of acute rejection is reduced. Corticosteroids have a hydrophobic structure that allows them to easily diffuse into cells and bind to specific cytoplasmic receptors. The resulting complexes progress to the nucleus, where they are able to inhibit the transcription of the genes of the cytokines named above.

Corticosteroids are also able to inhibit cytokine production in macrophages. This subsequently inhibits the macrophage phagocytosis and chemotaxis properties. Corticosteroids are also potent non-specific anti-inflammatory agents - administration of corticosteroids results in an acute reduction of circulating lymphocytes and monocytes.

Side effects observed with corticosteroid use include:

• hypertension
• hyperlipidemia
• osteoporosis
• weight gain
• a cushingoid appearance
• opportunistic infection
• glaucoma
• ulcer formation
• hyperglycemia (usually progressing to steroid diabetes)

Corticosteriods can be used to prevent, as well as to treat acute rejection. Oral, as well as intravenous routes are commonly used.

A high dose of intravenous methylprednisolone is usually given immediately before and during the transplantation procedure. Methylprednisolone or prednisone is often continued post-operatively for several days at high doses, and is then tapered to a maintenance dose. Dose and taper schedule varies with the organ transplanted.

Maintenance doses consist of orally administered prednisone, and are normally 5-10 mg/day