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

Answer: D. B cells and T cells PROTECT THE BODY FROM DISEASES CAUSED BY PATHOGENS. B CELLS and T CELLS are types of LYMPHOCYTES, the central cellular agents of the ADAPTIVE IMMUNE SYSTEM, which provides specific defence against pathogens (bacteria, viruses, fungi, parasites). B CELLS (Bone marrow-derived): - Mature in bone marrow. - Recognise antigens via membrane-bound B-cell receptors (immunoglobulins). - On activation, differentiate into plasma cells that secrete antibodies (IgM, IgG, IgA, IgD, IgE), neutralising pathogens and toxins. - Memory B cells provide long-term immunity (basis of vaccination). T CELLS (Thymus-matured): - Mature in the thymus. - Helper T cells (CD4+) coordinate immune responses by activating B cells and macrophages. - Cytotoxic T cells (CD8+) directly kill infected or cancerous cells. - Regulatory T cells modulate immune responses. Together they mount HUMORAL (B cell, antibody-mediated) and CELL-MEDIATED (T cell) immunity against pathogens. Distractors: (A) Allergens are environmental antigens; immune cells respond to them but 'protection from allergens' is a partial framing — allergic reactions are actually misdirected immune responses (mast cells, IgE, eosinophils). The PRIMARY role of B/T cells is anti-pathogen defence. (B) Pain and inflammation involve prostaglandins, cytokines, NSAIDs etc.; B and T cells do NOT alleviate pain. (C) B and T cells are NOT immunosuppressants — they are the active arm of immunity. Regulatory T cells modulate but do not 'suppress' immunity broadly. Source: NCERT Class 12 Biology Chapter 7 'Human Health and Disease' (immune system section).