Which of the following immune disorders is characterized by the immune system attacking and damaging its own body tissues?

Explanation: Antigens are unique molecules or proteins present on the surface of cells, including pathogens. The immune system can recognize these antigens as "non-self" and mount an immune response to eliminate them while sparing the body's own cells, which display different antigens that are recognized as "self."

Incorrect choices:

b. Recognizing different blood types is relevant for blood transfusions but not a primary mechanism of distinguishing self from non-self by the immune system.

c. Monitoring hormone levels in the body is not directly related to the immune system's ability to distinguish between self and non-self.

d. Cytokines are signaling molecules released by immune cells to regulate the immune response but are not the primary means of distinguishing self from non-self.

Explanation: Memory cells recognize and respond rapidly to previously encountered pathogens. Memory cells are a type of immune cell that are formed after an initial infection or vaccination. They "remember" the specific pathogen and allow the immune system to mount a faster and stronger response upon subsequent exposures to the same pathogen, providing long-term immunity.

Incorrect choices:

a. Memory cells do not directly attack pathogens in the body. They serve as a form of immune "memory" to help the body respond more effectively to future infections.

b. Memory cells do not produce antibodies upon initial pathogen exposure. B cells are responsible for producing antibodies in response to the pathogen.

d. Memory cells do not regulate the body's temperature during an infection. Temperature regulation is mainly controlled by the hypothalamus in the brain in response to infection or other stimuli.