Immunologic Aspects of Organ Transplantation

Susan Smith MN, PhD


June 17, 2002


Until the middle of the 20th century, attempts to transplant cadaveric organs terminated in rapid rejection of the donor organ. Although it was recognized that immune or genetic factors were responsible, only a few strategies (eg, total body and lymphoid irradiation) were available to suppress the vigorous response of the recipient immune system against the foreign graft. High rates of morbidity and mortality resulting from these myelotoxic strategies prohibited their widespread adoption and failed to advance transplantation into the clinic. During the last half of the 20th century, incredible progress was made in transplantation immunology and medicine. However, significant issues have yet to be overcome in man's quest for transplantation without immunosuppression.

The immune system is a large, complex network of mobile, interactive cells and molecules that circulate through the body's lymph and blood vessels, tissues, and organs to protect it from potentially harmful foreign molecules. This all-important property of immune responsiveness is also responsible for the major physiologic threat to organ transplantation -- rejection. Immunologic aspects of transplantation provide an important foundation for understanding how normal host defense mechanisms are triggered in response to transplanted organs. Transplantation immunology is a field that is constantly changing and evolving, and provides a basis for innovative research, education, and practice.

The objectives of this chapter are to:

  • Describe the basic anatomy and physiology of the immune system

  • Explain how the immune system responds to a foreign organ

  • Understand the rationale for immunosuppressive therapy

  • Examine the evidence that supports the current need for lifelong pharmacologic immunosuppression.