Which cells are primarily responsible for stimulating both the humoral and cell-mediated arms of the adaptive immune response?

• A. Macrophages
• B. Cytotoxic T cells (CD8+)
• C. Helper T cells (CD4+)
• D. B cells

Answer: (C)

Verified step by step guidance

1. Understand the two main arms of the adaptive immune response: the humoral response, which involves antibody production by B cells, and the cell-mediated response, which involves activation of cytotoxic T cells and other immune cells.
2. Identify the role of each cell type listed: Macrophages are primarily antigen-presenting cells and phagocytes; Cytotoxic T cells (CD8+) directly kill infected cells; B cells produce antibodies; Helper T cells (CD4+) assist other immune cells.
3. Recognize that Helper T cells (CD4+) are crucial because they secrete cytokines that activate B cells to produce antibodies (humoral response) and also stimulate cytotoxic T cells and macrophages (cell-mediated response).
4. Recall that Helper T cells recognize antigen presented by MHC class II molecules and then coordinate the immune response by 'helping' both arms of adaptive immunity.
5. Conclude that Helper T cells (CD4+) are the primary cells responsible for stimulating both the humoral and cell-mediated arms of the adaptive immune response.