Which of the following is NOT an antiphagocytic factor?

• A. Opsonization by antibodies
• B. Surface protein A expression
• C. Production of leukocidins
• D. Capsule formation

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the concept of antiphagocytic factors. These are mechanisms used by pathogens to avoid being engulfed and destroyed by phagocytes, which are immune cells responsible for ingesting harmful particles, bacteria, and dead or dying cells.
2. Step 2: Review each option to determine if it helps the pathogen evade phagocytosis. Surface protein A expression, production of leukocidins, and capsule formation are known antiphagocytic strategies because they interfere with phagocyte recognition, kill phagocytes, or physically block phagocytosis.
3. Step 3: Analyze opsonization by antibodies. Opsonization is a process where antibodies bind to pathogens, marking them for easier recognition and ingestion by phagocytes. This actually promotes phagocytosis rather than preventing it.
4. Step 4: Conclude that opsonization by antibodies is NOT an antiphagocytic factor because it enhances the immune system's ability to clear pathogens through phagocytosis.
5. Step 5: Summarize that the correct answer is opsonization by antibodies, as it facilitates phagocytosis, unlike the other options which inhibit it.