UPSC Prelims 2022 Q97: Role of B Cells and T Cells — Explained
Which one of the following statements best describes the role of B cells and T cells in the human body?
- They protect the body from environmental allergens.
- They alleviate the body's pain and inflammation.
- They act as immunosuppressants in the body.
- They protect the body from the diseases caused by pathogens.
Answer: (d) They protect the body from the diseases caused by pathogens.
Statement-wise explanation
- a: incorrect — B cells and T cells are not mainly there to protect the body from allergens such as pollen or dust. An allergy is the immune system overreacting to a harmless substance. B cells make IgE antibodies against the allergen, and mast cells then release histamine. So lymphocytes take part in causing allergic reactions. This statement describes a side-effect of immunity, not its job.
- b: incorrect — Painkillers and anti-inflammatory drugs such as NSAIDs and corticosteroids relieve pain and inflammation. Lymphocytes do not do this. When lymphocytes are activated they release cytokines, and these can add to inflammation.
- c: incorrect — An immunosuppressant is a drug that dampens the immune response. Examples are cyclosporin and corticosteroids, which are given after organ transplants. B and T cells are the main cells of the adaptive immune response, so they do the opposite. A small group of T cells, called regulatory T cells, does restrain immune reactions. That is a control job inside the system, not the overall role of B and T cells.
- d: correct — B and T lymphocytes carry out acquired (adaptive) immunity against pathogens. B cells mature into plasma cells that secrete antibodies; this is humoral immunity. Helper T cells coordinate the response. Cytotoxic T cells kill cells infected by viruses; this is cell-mediated immunity. Memory B and T cells give a faster response the next time the same pathogen appears.
How to eliminate
Basic school biology is enough. NCERT Class 12 Biology ('Human Health and Disease') says B and T lymphocytes produce acquired immunity, which defends the body against pathogens. The question asks what 'best describes' their role, so look for the main function, not a side-effect. Allergy is something the immune system causes, not something lymphocytes guard against. Pain and inflammation relief is what drugs do. 'Immunosuppressant' is a drug term, and it means the opposite of what immune cells do. Only one option states the textbook role. Fact to remember: B cells give antibody (humoral) immunity, and T cells give cell-mediated immunity.
Know more
Acquired immunity and lymphocytes
The body has two lines of defence. Innate immunity is present from birth and is non-specific: skin, mucus, stomach acid, phagocytes and natural killer cells. Acquired (adaptive) immunity is specific to each pathogen and has memory. B and T lymphocytes carry it out.
All lymphocytes are made in the bone marrow. B cells mature in the bone marrow and T cells mature in the thymus. These two are the primary lymphoid organs. Lymphocytes meet antigens in the secondary lymphoid organs: lymph nodes, spleen, tonsils, Peyer's patches and MALT.
| Feature | B cells | T cells |
|---|---|---|
| Matures in | Bone marrow | Thymus |
| Type of immunity | Humoral (antibody-mediated) | Cell-mediated |
| Main action | Become plasma cells that secrete antibodies (IgG, IgA, IgM, IgE, IgD) | Helper T cells coordinate the response; cytotoxic T cells kill infected and cancer cells |
| Key targets | Pathogens and toxins in body fluids | Virus-infected cells; graft rejection |
| Memory | Memory B cells | Memory T cells |
Primary vs secondary response. The first exposure to a pathogen gives a slow, weak response. A second exposure gives a fast, strong response because memory cells are already there. Vaccination is based on this.
Active vs passive immunity. In active immunity the body makes its own antibodies, after infection or vaccination. In passive immunity, ready-made antibodies are given. Examples are colostrum (IgA), antibodies crossing the placenta, and anti-venom or anti-tetanus serum.
When the system goes wrong
- Allergy: an overreaction to harmless allergens, driven by IgE, histamine and mast cells.
- Autoimmunity: the immune system attacks the body's own cells, as in rheumatoid arthritis.
- Immunodeficiency: HIV destroys helper T cells, which leads to AIDS.
- Immunosuppressants: drugs that deliberately damp down immunity, for example to prevent transplant rejection.
In the news
The question is tagged static. COVID-19 coverage in 2020–22 (antibody surveys, T-cell memory studies, vaccine-induced immunity) put antibody versus T-cell immunity in the news, which probably made the topic topical.