Subtopics - Health and Diseases (NEET)
Comprehensive guide to immunity, immune disorders, AIDS, allergies, autoimmunity, vaccination, and disease prevention for NEET
1) Immunity and Its Types
Immunity is the resistance of the body to disease, and immunology is the study of this resistance. B-lymphocytes originate and differentiate in bone marrow (Bursa of Fabricius in birds) and form the humoral/antibody-mediated immune system (AMIS), defending against extracellular pathogens in blood and lymph. T-lymphocytes differentiate in the thymus and form the cell-mediated immune system (CMIS), defending against intracellular pathogens including protists and fungi. Immunity is classified as innate (inherited, present from birth, e.g. humans immune to canine distemper) or acquired/adaptive. Acquired immunity is further divided into active immunity (own cells produce antibodies after infection or vaccination, long-lasting) and passive immunity (preformed antibodies injected from another organism, provides immediate but short-lived relief, e.g. anti-tetanus serum, anti-rabies serum). Colostrum transfers maternal IgA antibodies to nursing infants as a form of natural passive immunity.
2) Allergies and Autoimmune Diseases
Allergies are hypersensitivity reactions to foreign substances called allergens (dust, pollen, mould spores, foods, drugs). During allergic reactions, mast cells release histamine, causing vasodilation and increased capillary permeability. Three major allergic conditions are hay fever (affects nose, eyes, upper respiratory tract; treated with antihistamines), asthma (swelling of respiratory tube tissues causing breathing difficulty), and anaphylactic shock (systemic reaction after antigen injection like penicillin, causing drastic blood pressure drop, potentially fatal). Autoimmunity occurs when the immune system attacks self-antigens (autoantigens). The resulting autoimmune diseases depend on the autoantigen involved: RBC destruction causes chronic anaemia, muscle cell targeting causes myasthenia gravis, liver cell targeting causes chronic hepatitis. Other autoimmune diseases include rheumatoid arthritis, juvenile diabetes, Addison's disease, ulcerative colitis, Grave's disease, systemic lupus erythematosus, and scleroderma.
3) Immunodeficiencies and AIDS
Immunodeficiency disorders include Severe Combined Immunodeficiency (SCID), a congenital disease where both B-cells and T-cells are absent, making children highly susceptible to even minor infections. Acquired Immune Deficiency Syndrome (AIDS) is a disorder of cell-mediated immunity caused by HIV, which reduces helper T-cell numbers and destroys the body's natural defence. AIDS was first noticed in 1981 by Gottlies in USA homosexuals; the virus was isolated by Prof. Luc Montagnier (France, 1983) and Prof. Robert Gallo (USA). In India, AIDS was first detected in Chennai prostitutes in 1986. HIV infection progresses through three stages: asymptomatic carrier (1-2% show initial symptoms, highly infectious, antibody test becomes positive), AIDS Related Complex (ARC, swollen lymph glands for 3+ months, night sweats, persistent diarrhoea, memory loss), and full-blown AIDS (severe weight loss, opportunistic infections including Pneumocystis carinii pneumonia, Kaposi's sarcoma, toxoplasmic encephalitis). Diagnosis uses ELISA test confirmed by western blot. Treatment includes zidovudine (AZT) and DDI. HIV transmits via sexual contact, infected blood/needles, and mother-to-child (placenta, birth canal, breast milk).
4) Vaccines and Vaccination
Vaccination was initiated by Edward Jenner in 1790, who observed that milkmaids exposed to cowpox did not contract smallpox. He inoculated James Phipps with cowpox and later showed the boy was immune to smallpox. The term vaccine comes from Latin vacca (cow). Louis Pasteur confirmed Jenner's findings and developed vaccines for anthrax, rabies, and chicken cholera. Calmette and Guerin developed BCG vaccine for tuberculosis; Salk and Sabin developed polio vaccines; Enders developed the measles vaccine. WHO launched the Global Immunisation Programme in 1974 for six diseases (diphtheria, pertussis, tetanus, measles, TB, polio). Vaccines are classified into five types: killed vaccines (pathogen killed by heat/UV/formalin, e.g. typhoid and cholera vaccines), toxoids (toxin retains antigenicity but loses toxicity, e.g. tetanus toxoid, diphtheria toxoid), attenuated live vaccines (weakened non-virulent pathogen, e.g. OPV, BCG, MMR; provide lifelong active immunity), antibody-based vaccines (serum containing antibodies, provides passive immunity, e.g. ATS, anti-rabies serum), and polysaccharide/protein vaccines (e.g. pneumococcal polysaccharides, interferon).
Health and Diseases Download Notes & Weightage Plan
For each topic in the Health and Diseases chapter below, you get (2) the exact resources to download and how to use them, and (3) a simple importance & time plan so NEET students know what to do first and what to revise last.
Covers B-cell vs T-cell distinction, innate vs acquired immunity, active vs passive immunity, and colostrum-mediated passive immunity. Central to understanding all downstream immunology topics in the chapter.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: B-cell vs T-cell origin and function, active vs passive immunity comparison, colostrum IgA, innate immunity examples (human immunity to canine distemper), helper T-cell role in stimulating B-cell antibody production.
- High-risk Area: Confusing active immunity (own cells produce antibodies) with passive immunity (preformed antibodies injected). Forgetting that helper T-cells stimulate B-cells. Mixing up IgA (colostrum) with IgG or IgM.
- Best Practice Style: Table + Flowchart
Allergies and Autoimmune Diseases
Covers allergic reactions mediated by histamine from mast cells, types of allergies (hay fever, asthma, anaphylactic shock), and autoimmune diseases where the immune system attacks self-antigens. Includes the comprehensive autoimmune disorders table.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: IgE antibody in allergy, histamine from mast cells, anaphylactic shock mechanism (penicillin trigger, BP drop), autoimmune disease-autoantigen pairs for rheumatoid arthritis, myasthenia gravis, juvenile diabetes, lupus, and Grave's disease.
- High-risk Area: Selecting IgG instead of IgE as the allergy antibody. Confusing autoimmune diseases with immunodeficiency diseases. Not recognising that anaphylactic shock can be fatal due to blood pressure crash.
- Best Practice Style: Table + Mechanism Diagram
Covers SCID as primary immunodeficiency and AIDS as acquired immunodeficiency. Details HIV discovery, three stages of infection, opportunistic infections, ELISA and western blot diagnosis, zidovudine treatment, transmission modes, and prevention strategies. Includes hepatitis A and B.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: HIV attacks helper T-cells (T4 lymphocytes), ELISA test for diagnosis, western blot for confirmation, zidovudine (AZT) treatment, Pneumocystis carinii pneumonia as indicator of full-blown AIDS, mother-to-child transmission routes, SCID = absence of both B and T cells.
- High-risk Area: Confusing ELISA (diagnosis) with western blot (confirmation). Forgetting that HIV specifically targets helper T-cells not all T-cells. Stating AIDS can spread through casual contact. Mixing up Hepatitis A (faecal-oral, no liver damage) with Hepatitis B (blood-borne, liver cell swelling).
- Best Practice Style: Flowchart + Timeline
Covers the history from Jenner's cowpox experiment through Pasteur's contributions and WHO immunisation programme. Classifies vaccines into five types with specific examples. Includes the comprehensive vaccine table with BCG, OPV, DPT, MMR, TAB and immunisation schedule details.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Jenner's cowpox experiment and vaccine etymology, five vaccine types with examples, BCG = live attenuated for TB, OPV = live for polio, DPT = toxoid for diphtheria-pertussis-tetanus, TAB = killed for typhoid, WHO 1974 programme for 6 diseases.
- High-risk Area: Misclassifying DPT as killed vaccine instead of toxoid. Confusing Salk (injectable, killed polio vaccine) with Sabin (oral, live polio vaccine). Forgetting that attenuated live vaccines provide lifelong immunity. Mixing up BCG's target (tuberculosis, not plague).
- Best Practice Style: Table + Flash Cards
Health and Diseases Chapter NEET Traps & Common Mistakes (Topic-Wise)
Each subtopic below is of the Health and Diseases chapter and shows what NEET students usually do wrong in NEET examination, a short example of the mistake, and how NEET frames the question to trick you with close options are given below.
Mistake Snapshot (What Students Do Wrong)
- Swapping active and passive: Students confuse active immunity (body's own cells produce antibodies, long-lasting, develops after infection or vaccination) with passive immunity (preformed antibodies from another organism injected, short-lived, immediate effect). Anti-snake venom is passive, not active.
- Colostrum antibody class error: Colostrum contains IgA antibodies transferred from mother to nursing infant. Students often incorrectly select IgG or IgM. IgA is specifically associated with mucosal immunity and secretions including breast milk.
A NEET question asks: 'Injection of anti-snake venom is an example of which type of immunity?' The correct answer is passive immunity (artificially acquired), because preformed antibodies are injected. Students selecting 'active immunity' forget that active immunity requires the body to produce its own antibodies.
How NEET Frames The Trap
NEET exploits the active-passive confusion by presenting clinical scenarios (anti-venom, anti-tetanus serum) and asking which immunity type applies. The word 'injection' misleads students into thinking it is vaccination (active).
Q. Colostrum, the yellowish fluid secreted by mother during initial lactation days, provides immunity to the newborn because it contains:
A. IgA B. IgG C. IgE D. Natural killer cells
Trick: The correct answer is IgA. NEET 2019 tested this exact concept. IgA is the predominant immunoglobulin in mucosal secretions including colostrum and breast milk. Students picking IgG confuse it with the most abundant serum immunoglobulin, while IgE is associated with allergies.
Mistake Snapshot (What Students Do Wrong)
- Wrong immunoglobulin for allergy: Allergic reactions are mediated by IgE antibodies, not IgG. IgE binds to mast cell surfaces and triggers histamine release upon allergen re-exposure. Students frequently select IgG because it is the most abundant immunoglobulin in blood.
- Confusing allergy with autoimmunity: Allergy is hypersensitivity to external foreign substances (allergens). Autoimmunity is the immune system attacking self-antigens. Students mix these up because both involve immune system dysfunction, but the target is different: external in allergy, internal in autoimmunity.
A question asks: 'Which antibody is produced during an allergic reaction?' Many students select IgG (most common blood antibody) or IgM (first response antibody). The correct answer is IgE, which is specifically involved in type I hypersensitivity reactions and binds to mast cells, triggering histamine release upon allergen contact.
How NEET Frames The Trap
NEET often lists all five immunoglobulin classes as options when asking about allergy. Students who know IgG is the most abundant serum antibody instinctively select it, but allergy specifically involves IgE-mediated mast cell degranulation.
Q. The antibodies involved in allergic reactions belong to which class?
A. IgA B. IgE C. IgG D. IgM
Trick: The correct answer is IgE. This has been asked repeatedly in NEET, Kerala PMT, and AMU. IgE binds to mast cell surfaces and cross-links upon allergen binding, causing histamine release. IgG is the most abundant serum antibody but is not involved in type I hypersensitivity.
Mistake Snapshot (What Students Do Wrong)
- HIV targets all T-cells error: HIV specifically infects and destroys helper T-cells (T4/CD4+ lymphocytes), not all T-cells. Students often generalise by saying HIV attacks 'all lymphocytes' or 'all T-cells'. The reduction in helper T-cells is what collapses the immune system because they stimulate both B-cell antibody production and killer T-cell activity.
- ELISA vs Western Blot confusion: ELISA (Enzyme-linked immunosorbent assay) is the primary screening test for HIV antibodies. A positive ELISA must be confirmed by western blot test. Students confuse which test comes first or treat them as interchangeable. ELISA screens, western blot confirms.
A NEET question states: 'HIV causes reduction in ____.' Options include all lymphocytes, all T-cells, T-helper cells only, and B-cells only. The correct answer is T-helper cells only. HIV binds to CD4 receptors on helper T-cells via its GP120 surface protein. This has been tested in MP PMT, BHU, CBSE PMT, and NEET multiple times.
How NEET Frames The Trap
Questions present 'all T-cells' or 'all lymphocytes' as choices alongside 'T-helper cells only'. The broader options seem safer, but HIV specifically targets CD4+ helper T-cells. The specificity of the answer is what NEET tests.
Q. HIV virus specifically attacks which cells in the human immune system?
A. B-lymphocytes B. T-helper cells (CD4+) C. All T-lymphocytes D. Cytotoxic T-cells
Trick: The correct answer is T-helper cells (CD4+). HIV's GP120 envelope protein binds to CD4 receptors specifically present on helper T-cells. Selecting 'all T-lymphocytes' is the most common mistake because students overgeneralise. Cytotoxic T-cells (CD8+) are not the primary target.
Mistake Snapshot (What Students Do Wrong)
- DPT is not a killed vaccine: DPT (Diphtheria, Pertussis, Tetanus) is classified as a toxoid vaccine because it contains inactivated toxins that retain antigenicity. Students frequently misclassify it as a killed vaccine. TAB (typhoid) and cholera vaccine are killed vaccines.
- Salk vs Sabin polio vaccine confusion: Salk developed the injectable killed/inactivated polio vaccine (IPV). Sabin developed the oral live attenuated polio vaccine (OPV). Students confuse which scientist made which type. In India, OPV (Sabin) is the standard for mass immunisation.
A question asks: 'Match Tuberculosis with the correct vaccine type: (I) Harmless virus, (II) Inactivated toxin, (III) Killed bacteria, (IV) Harmless bacteria.' Students selecting (III) killed bacteria are wrong. BCG is a live attenuated (harmless) bacteria vaccine, matching option (IV). This was tested in AIPMT 2015.
How NEET Frames The Trap
NEET presents vaccine classification matching questions where BCG (live attenuated bacteria) is confused with killed bacteria, and DPT (toxoid) is confused with killed vaccine. The key is knowing that live attenuated vaccines provide lifelong immunity while killed vaccines require boosters.
Q. Which of the following is an example of a toxoid vaccine?
A. BCG B. OPV (Oral Polio Vaccine) C. DPT (Diphtheria, Pertussis, Tetanus) D. TAB (Typhoid vaccine)
Trick: The correct answer is DPT. A toxoid vaccine contains bacterial toxin that has lost its toxicity but retains antigenicity. BCG and OPV are live attenuated vaccines. TAB is a killed vaccine. Students picking TAB confuse 'killed organism' with 'inactivated toxin'.