What are the body's 3 lines of defense against infection?

• A. Fever, white blood cells, antibodies
• B. Mucous membranes, enzymes, skin
• C. Skin, hair, nails
• D. Unbroken skin, inflammation, antibodies

Answer: (D)

Think of the body's defenses as three layers. The first line is a barrier that stops microbes at the entry point, with unbroken skin being the classic example. When invaders get past that barrier, the second line activates—innate defenses such as inflammation that bring immune cells to the area and help control the threat. The third line is adaptive immunity, which uses antibodies produced by B cells to specifically recognize and neutralize pathogens.

This option fits best because it includes an element from each line: unbroken skin for the first line, inflammation for the second line, and antibodies for the third line. The other choices either emphasize only one line or omit a line entirely (for example, listing only barriers or only innate responses), so they don’t represent all three layers of defense.