Which of the following best describes the action of an antigen-presenting cell (APC) after it engulfs a microbe?

• A. It digests the microbe and displays microbial antigens on its surface using major histocompatibility complex (MHC) molecules.
• B. It destroys the microbe and releases cytokines without presenting any antigens.
• C. It transports the microbe intact to the lymph nodes for destruction.
• D. It immediately releases antibodies to neutralize the microbe.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the role of antigen-presenting cells (APCs) in the immune response. APCs, such as dendritic cells, macrophages, and B cells, are responsible for detecting, engulfing, and processing pathogens.
2. Step 2: Recognize that after engulfing a microbe, APCs break down the microbe into smaller pieces called antigens through a process called digestion or proteolysis inside specialized compartments.
3. Step 3: Learn that these processed microbial antigens are then loaded onto major histocompatibility complex (MHC) molecules within the APC.
4. Step 4: The APC transports the MHC-antigen complex to its cell surface, effectively displaying the microbial antigens to T cells, which is crucial for activating the adaptive immune response.
5. Step 5: Conclude that the best description of APC action after engulfing a microbe is that it digests the microbe and presents microbial antigens on its surface using MHC molecules, enabling T cell recognition and immune activation.