Graft transplantation to save certain patients fails due to the rejection of such organs by the patient. Which type of immune response is responsible for such type of rejection?

The type of immune response responsible for the rejection of transplanted organs is called the adaptive immune response. Here are the steps explaining why:

1. When a new organ is transplanted into a patient's body, the immune system recognizes the cells of this organ as foreign due to the presence of different antigens on the surface of the cells.

2. This recognition triggers the adaptive immune response. The adaptive immune system is highly specific and is capable of recognizing and remembering specific pathogens to generate immunity, and thus it responds to the foreign antigens.

3. The cells involved in this process are primarily T cells and B cells. T cells are responsible for cell-mediated immunity whereas B cells are responsible for humoral immunity.

4. T cells recognize the foreign antigens presented on the cells of the transplanted organ and start to multiply, producing more T cells that can recognize the same antigen. Some of these T cells become cytotoxic T cells, which can kill the cells presenting the foreign antigen.

5. B cells, on the other hand, produce antibodies against the foreign antigens. These antibodies can bind to the antigens and mark them for destruction by other immune cells.

6. This immune response against the transplanted organ leads to its rejection.

To prevent this, patients are often given immunosuppressive drugs to reduce the activity of the immune system and prevent the rejection of the transplanted organ. However, these drugs also increase the risk of infections and other diseases because they suppress the immune system as a whole.