Correct Option (D)
B cells and T cells are central components of the adaptive (acquired) immune system.
- B lymphocytes (B cells) are primarily responsible for humoral immunity, producing specific antibodies that target and neutralize extracellular pathogens (bacteria, viruses in body fluids) and toxins.
- T lymphocytes (T cells) mediate cell-mediated immunity. They include cytotoxic T cells (which directly kill infected or cancerous cells) and helper T cells (which coordinate the immune response by activating other immune cells, including B cells and cytotoxic T cells).
Their combined action provides specific and long-lasting protection against a wide range of diseases caused by various pathogens.
Incorrect Options:
Option (A): While B and T cells are part of the overall immune system, their primary and direct role is not limited to or best described as protecting against environmental allergens. Allergic reactions often involve other immune components such as mast cells and IgE antibodies, though T cells can influence these responses.
Option (B): Pain and inflammation are complex physiological responses primarily mediated by chemical signals and cellular components like mast cells, macrophages, and various cytokines and prostaglandins. B and T cells do not directly alleviate pain or inflammation; rather, they are involved in specific immune responses to pathogens or abnormal cells.
Option (C): B and T cells are crucial for initiating, developing, and regulating robust immune responses against threats. They are effector cells of the immune system, actively fighting infections and abnormal cells. Immunosuppressants are substances, often drugs, that suppress or reduce the activity of the immune system, frequently by targeting B and T cell functions, for example, in organ transplantation or autoimmune diseases.