The immune system is responsible for controlling the body's response to various types of injury and for defending the body from invading pathogens, including bacteria, viruses, and other parasites.1,2 The importance of this system in maintaining health is illustrated by the devastating effects that can occur in people who lack adequate immune function, such as patients with AIDS. The use of drugs to modify immune responses, or immunomodulating agents, is therefore an important area of pharmacology. For example, it may be helpful to augment immune function if a person's immune system is not functioning adequately. By contrast, it is sometimes necessary to suppress immune function pharmacologically to prevent immune-mediated injury to certain tissues or organs. Following organ transplants and tissue grafts, the immune system may cause the rejection of tissues transplanted from other donors (allografts) or from other sites in the patient's body (autografts).3,4 Likewise, immunosuppression may be helpful when the immune system causes damage to the body's tissues. Such conditions are often referred to as autoimmune diseases. Clinical disorders such as rheumatoid arthritis, multiple sclerosis, and systemic lupus erythematosus (SLE) are now recognized as having an autoimmune basis.5,6
This chapter begins with a brief overview of the immune response, followed by the drugs that are currently available to suppress or stimulate this response. Immunosuppressive drugs, or immunosuppressants, can prevent the rejection of transplants or treat specific diseases caused by an autoimmune response. Clearly, these drugs must be used very cautiously because too much suppression of the immune system will increase a patient's susceptibility to infection from foreign pathogens.7 Likewise, these drugs are rather toxic and often cause several adverse effects to the kidneys, lungs, musculoskeletal system, and other tissues. Nonetheless, immunosuppressive agents are often lifesaving because of their ability to prevent and treat organ rejection and to decrease immune-mediated tissue damage in other diseases. The group of drugs that increase immune function, or immunostimulants, is rather small and the clinical use of immunostimulants is limited when compared with the indications for immunosuppressive drugs. However, the development and use of immunostimulants is an exciting area of pharmacology, and some insight into the therapeutic use of these drugs is provided.
Physical therapists and occupational therapists may be involved in the rehabilitation of patients who have received organ transplants, skin grafts, or similar procedures that necessitate the use of immunosuppressant drugs. Rehabilitation specialists also treat patients with autoimmune disorders or immunodeficiency syndromes that affect the musculoskeletal system; these patients are also likely to be taking immunomodulating drugs. Hence, this chapter will provide therapists with knowledge about the pharmacology of these drugs and how their effects and side effects can affect physical rehabilitation.
OVERVIEW OF THE IMMUNE RESPONSE
One of the primary responsibilities of the immune system is to protect the body from bacteria, viruses, and other foreign pathogens. ...