Which one of the following statements best describes the role of B cells and T cells in the human body?

1. The question asks for the statement that best describes the role of B cells and T cells in the human body. 2. B cells (B lymphocytes) and T cells (T lymphocytes) are the major components of the adaptive immune system. 3. B cells are primarily responsible for producing antibodies that target specific extracellular pathogens (like bacteria) and toxins. 4. T cells have various roles, including helping B cells (helper T cells) and directly killing infected host cells (cytotoxic T cells), thus fighting intracellular pathogens (like viruses) and cancerous cells. 5. Option (A) is too narrow; while the immune system reacts to allergens, the primary role of B and T cells is broader defense against infectious agents. 6. Option (B) is incorrect; while immune responses can involve inflammation, B and T cells don't primarily alleviate pain and inflammation; their activation often contributes to it as part of the defense mechanism. 7. Option (C) is incorrect; B and T cells are key effectors of the immune response, not immunosuppressants. 8. Option (D) accurately summarizes their fundamental role: they protect the body from the diseases caused by pathogens through adaptive immunity. 9. Therefore, option (D) is the best description.