Which of the following is the third step in the process that elicits an antibody response during adaptive immunity?

• A. Phagocytosis of pathogens by macrophages
• B. Activation of helper T cells by antigen-presenting cells
• C. Secretion of antibodies by plasma cells
• D. Recognition of antigen by B cell receptors

Answer: (B)

Verified step by step guidance

1. Understand the overall process of adaptive immunity, which involves several key steps: recognition of the antigen, processing and presentation of the antigen, activation of helper T cells, activation of B cells, and finally secretion of antibodies.
2. Identify the first step: Phagocytosis of pathogens by macrophages, where macrophages engulf and digest pathogens to process their antigens.
3. Recognize the second step: Presentation of processed antigen fragments on the surface of macrophages (antigen-presenting cells) to helper T cells.
4. Determine the third step: Activation of helper T cells by antigen-presenting cells, where helper T cells recognize the antigen-MHC complex and become activated.
5. Note that subsequent steps include activation of B cells by helper T cells and secretion of antibodies by plasma cells, which occur after helper T cell activation.