Immunity, Vaccination, Allergy and AIDS: Quick Revision

A brief note on Immunity, Vaccination, Allergy and AIDS. Read it before a test. Try each question at the end before you open its answer.

Innate immunity

• Innate immunity: present from birth, non-specific.
• Four barriers: physical (skin, mucus), physiological (stomach acid, saliva, tears), cellular (neutrophils, monocytes, macrophages, natural killer cells) and cytokine (interferons).
• Primary lymphoid organs: bone marrow and thymus. Secondary: spleen, lymph nodes, tonsils, Peyer's patches, appendix and MALT. MALT is about half of the lymphoid tissue.

Acquired immunity

• Specific, with a memory. The primary response is slow and low. The secondary response is quick and strong.
• B cells: make antibodies (humoral response). T cells: the cell-mediated response, which also rejects grafts.
• Antibody: two heavy and two light chains, H$_2$L$_2$. Classes: IgA, IgM, IgE, IgG.
• Active immunity: the body makes the antibodies, slowly. Passive: ready-made antibodies, quickly. Colostrum (IgA) and the placenta give passive immunity.
• Vaccine: makes memory cells. Tetanus antitoxin and antivenom are passive.

Allergy, autoimmunity and AIDS

• Allergy: IgE on mast cells, release of histamine and serotonin. Anti-histamine, adrenaline and steroids help.
• Autoimmunity: the body attacks its own cells. Example: rheumatoid arthritis.
• HIV: a retrovirus with an RNA genome. Reverse transcriptase makes DNA, which joins the host DNA. It destroys the helper T cells and macrophages are its factories.
• Spread: sexual contact, infected blood, shared needles, mother to child. Not by touch. Test: ELISA. Prevention is the best option.

A worked example

100000 germs arrive. A barrier stops 80 per cent, and the next barrier stops 50 per cent of the rest. How many are left?

1. After the first barrier, 20 per cent are left: 20000.
2. After the second barrier, half of them are left: 10000.

Practice with new numbers

A program to try

The program counts the barriers of innate immunity by type.

Mistakes to avoid

• Saying that T cells make antibodies. The B cells make them.
• Calling a vaccine passive. It is active. An antitoxin is passive.
• Saying that HIV spreads by touch. It does not.
• Mixing up allergy and autoimmunity. Allergy is a reaction to an outside substance.

Check yourself

1. Which antibody is in the colostrum?

2. Which cells does HIV destroy?

3. Which two organs are the primary lymphoid organs?

4. Which chemicals cause the symptoms of an allergy?

Sources

• Murphy K. and Weaver C. (2017). Janeway's Immunobiology, 9th edition, Garland Science.
• World Health Organization (2024). Fact sheet: HIV and AIDS.
• NCERT (2023). Biology, Textbook for Class XII, chapter 7.