What part of the immune system is involved in organ rejection?

All of it!: Our immune system is very complex and is designed to protect us from the outside world. We used to think that the primary defense came from the t-cell system, but when this system is suppressed, the b-cell system can kick in too. This is why tolerance has been so hard to achieve. Every time we think we have it licked, another part of the immune system steps up to cause problems.

Innate and Adaptive: Innate or non-specific immunity involves the skin, lining of the GI tract, respiratory tract, gu tract, etc; and adaptive immunity that involves cells (primarily lymphocytes). Both types of immunity can affect the graft and trigger rejection. In addition, immune responses involve the formation of both cells and antibodies (proteins) that are reactive against the transplanted organ.

Immune System is: Categorized by: 1. Humoral, antibody driven, under influence of the gut/bursa fabricius analog influence b-cells; and 2. Cell-mediated, t-cell mediated. The t-cells have memory (mesles, mumps, chicken pox), recognize self vs other orga antigens, fight fungi. The t stands for thymus, an organ developing 3rd 4rth branchial pouch, along wth parathyroid. Thymus involutes in adults.