Question

which of the following is a component of the immune systems third line of defense?
○ mucus
○ t cells
○ platelets
○ macrophages

Explanation:

The immune system has three lines of defense. The first line (mucus, skin, etc.) is physical/chemical. The second line (macrophages, inflammation) is innate. The third line is adaptive immunity, involving lymphocytes like T cells (and B cells). Mucus is first line, platelets are for blood clotting, macrophages are second line. T cells are part of the adaptive (third) line.

Answer:

B. T cells