Question

Different MHC class I molecules between donor and recipient cells can lead to rejection of a transplanted organ or tissue. Suggest a reason for this.

Short answer

Answer: The reason for organ or tissue rejection due to different MHC class I molecules between donor and recipient cells is that these different molecules are recognized as foreign by the recipient's immune system. This leads to an immune response, specifically by cytotoxic T cells, which target and kill cells expressing the foreign MHC molecules. Consequently, the transplanted organ or tissue is rejected as the recipient's immune system works to eliminate the perceived foreign cells.

Step-by-step solution

Introduce MHC class I molecules

MHC class I molecules are present on the surface of all nucleated cells and play a crucial role in the body's immune system. Their main function is to recognize and bind to foreign proteins (such as those from viruses or bacteria) and present them to the immune system, specifically to cytotoxic T cells.

Explain the role of cytotoxic T cells

Cytotoxic T cells are an essential part of the adaptive immune system, and their primary function is to kill infected or abnormal cells. Once a cytotoxic T cell recognizes and binds to an MHC class I molecule presenting a foreign protein on a target cell's surface, it releases molecules that induce apoptosis (cell death) of the target cell, thus eliminating the infected or abnormal cell.

Describe the importance of MHC class I molecule diversity

MHC class I molecules are highly polymorphic, meaning that there is a significant level of genetic variation between individuals. This diversity ensures that the immune system can recognize and respond to a wide variety of foreign proteins. However, this also means that each individual's MHC class I molecules are distinct enough that they can be recognized as foreign by the immune system of another individual.

Explain how differences in MHC class I molecules can lead to organ rejection

During an organ or tissue transplant, the donor cells express MHC class I molecules that may differ from those of the recipient. As a result, the recipient's immune system, specifically the cytotoxic T cells, can recognize the donor cells as foreign, leading to an immune response against the transplanted organ or tissue. This immune response ultimately results in the rejection of the transplanted organ or tissue, as the recipient's immune system works to eliminate the perceived foreign cells.

Conclude with the reason for organ rejection

In conclusion, the reason for organ or tissue rejection due to different MHC class I molecules between donor and recipient cells is that these different molecules are recognized as foreign by the recipient's immune system. This leads to an immune response and ultimately, the rejection of the transplanted organ or tissue. The immune system's ability to recognize and respond to foreign substances is essential for protecting the recipient from harmful infections and diseases, but it can also result in complications like organ rejection during transplantation.