In autoimmune illnesses like rheumatoid arthritis, the body's ________ system attacks normal tissue.

In autoimmune illnesses such as rheumatoid arthritis, the body's immune system is misled into attacking its own healthy tissues. In a normal scenario, the immune system is designed to protect the body from foreign pathogens like viruses and bacteria. However, in autoimmune conditions, this defense mechanism mistakenly targets the body's own cells, leading to inflammation and tissue damage.

Rheumatoid arthritis specifically involves the immune system attacking the joints, causing pain and swelling. This dysfunction in immune response is a hallmark of autoimmune diseases, which makes understanding the role of the immune system crucial for both diagnosis and treatment of such conditions. The other systems mentioned—lymphatic, circulatory, and endocrine—have important roles in the body, but they do not specifically involve the immune response that characterizes autoimmune disorders.