Which of the following innate defense mechanisms can lyse bacteria and mark cells for phagocytosis?

• A. Complement system
• B. Interferons
• C. Natural killer (NK) cells
• D. Mucous membranes

Answer: (A)

Verified step by step guidance

1. Understand the question: The problem is asking which innate defense mechanism can both lyse bacteria and mark cells for phagocytosis. This requires knowledge of the immune system's innate defenses.
2. Review the innate defense mechanisms: The innate immune system includes several components such as the complement system, interferons, natural killer (NK) cells, and physical barriers like mucous membranes. Each has a specific role in defending the body.
3. Analyze the complement system: The complement system is a group of proteins that, when activated, can directly lyse bacterial cells by forming a membrane attack complex (MAC). Additionally, it can opsonize (mark) pathogens for phagocytosis by coating them with complement proteins.
4. Evaluate the other options: Interferons are signaling proteins that help inhibit viral replication but do not lyse bacteria or mark cells for phagocytosis. NK cells target and kill infected or abnormal host cells but do not directly lyse bacteria or mark them. Mucous membranes act as physical barriers to trap pathogens but do not perform lysis or marking.
5. Conclude: Based on the analysis, the complement system is the innate defense mechanism that can both lyse bacteria and mark cells for phagocytosis.