What phrase best describes immunosuppression?

• A. A lowered immune responsiveness
• B. The inability to recognize a substance as nonself
• C. An illness produced by circulating complexes of antibody and antigen
• D. All of the above

Answer: (A)

Immunosuppression is a reduced capacity of the immune system to respond to challenges. The best description is a lowered immune responsiveness because the body’s defense mechanisms—cells, antibodies, and signaling molecules—are less able to mount a full reaction to infections, vaccines, or transplanted tissue. This can result from drugs that dampen immune activity, illnesses that deplete immune cells, poor nutrition, stress, or aging.

The other descriptions aren’t the same thing. An inability to recognize a substance as nonself points to immune tolerance or anergy, where the immune system doesn’t react appropriately to foreign material, not a general reduction in responsiveness. Circulating immune complexes describe a pathology where antibodies and antigens form complexes that cause disease, which is a different mechanism from immunosuppression.