Which of the following cell groups is associated with the innate immune system?

• A. Mast cells, phagocytes, and natural killer cells
• B. Lymphocytes (B-cells and T-cells)
• C. Antibodies
• D. Dendritic cells

Answer: (A)

Immediate, non-specific defense is the hallmark of the innate immune system. Mast cells react to tissue signals by releasing histamine and other mediators that trigger inflammation and recruit more immune cells. Phagocytes, including neutrophils and macrophages, ingest and destroy pathogens in a non-specific way, forming a first line of defense. Natural killer cells patrol for virus-infected or abnormal (cancerous) cells and kill them without needing prior exposure to a specific antigen. Together, these cells provide rapid, general protection at the site of infection and throughout the body.

Lymphocytes (B and T cells) and antibodies belong to adaptive immunity, which is specific to particular pathogens and builds memory for faster responses upon re-exposure. Dendritic cells are essential for presenting captured antigens to T cells and thus bridging innate and adaptive responses, but they are best understood as mediators that activate the adaptive arm rather than primary innate effectors.

So the group described—mast cells, phagocytes, and natural killer cells—best represents innate immunity because they act quickly and non-specifically to defend against invading pathogens.