Microbiology Cheat Sheet
Immunity & Vaccine Logic
Immunity and vaccine logic for NEET-PG: innate vs adaptive immunity, immunoglobulin classes, MHC rule of 8, conjugate vaccines, and India's UIP schedule.
MedNext Academy | 3 min read
Immunity & Vaccine Logic
Immunity and vaccine logic for NEET-PG: innate vs adaptive immunity, immunoglobulin classes, MHC rule of 8, conjugate vaccines, and India's UIP schedule.
This topic covers innate and adaptive immune mechanisms, immunoglobulin structure and function, and the immunological basis of vaccines and India's immunisation schedule.
High-yield lines
- Innate immunity is immediate and non-specific using germline-encoded pattern recognition receptors, while adaptive immunity is delayed, specific, and generates memory.
- TLR4 recognises Gram-negative lipopolysaccharide via MD-2 and CD14, and excessive signalling drives the cytokine storm of septic shock.
- C5a is the most potent chemotactic complement anaphylatoxin, while the membrane attack complex (C5b to C9) is particularly effective against Neisseria.
- IgG is the only immunoglobulin that crosses the placenta, providing passive neonatal immunity, and is the predominant antibody of the secondary response.
- IgM is the first antibody produced in a primary response, is a pentamer, and is the most efficient complement activator.
- Secretory IgA is the predominant immunoglobulin in mucosal secretions, saliva, tears, and breast milk, and resists proteolysis via the secretory component.
- IgE binds mast cells and basophils to mediate type I hypersensitivity and anti-helminth defence.
- MHC class I presents endogenous peptides to CD8 T cells, while MHC class II presents exogenous peptides to CD4 T cells (the rule of 8).
- Th1 cells activate macrophages for intracellular pathogen defence, while Th2 cells drive IgE class switching and helminth defence.
- Live attenuated vaccines such as BCG, OPV, and MMR give strong humoral and cellular immunity but are contraindicated in immunocompromised and pregnant individuals.
- Conjugate vaccines link polysaccharide antigens to protein carriers, converting T-independent responses into T-dependent ones effective in infants under 2 years.
- Polysaccharide vaccines are T-independent, produce mainly IgM, generate no memory, and are poorly immunogenic in children under 2 years.
- In India's UIP, BCG, OPV-0, and hepatitis B birth dose are given at birth, with pentavalent, OPV, rotavirus, and PCV in the primary series.
- The herd immunity threshold is calculated as 1 minus 1 divided by R0, requiring about 92 to 95 percent for measles.
Mapped competency codes
- MI1.7
- MI1.8
- MI1.9
Continue into the full chapter
This summary maps to MI1-general-microbiology-and-immunity.
Frequently Asked Questions
Which immunoglobulin crosses the placenta?
IgG, which provides passive immunity to the neonate for the first 3 to 6 months of life.
Why are conjugate vaccines effective in infants under 2 years?
They link the polysaccharide antigen to a protein carrier, converting a T-independent response into a T-dependent one that generates IgG and memory.
What does TLR4 recognise and what is the consequence of overactivation?
TLR4 recognises Gram-negative lipopolysaccharide via MD-2 and CD14, and excessive signalling drives septic shock via TNF-alpha and IL-1.
Which antibody is first produced in a primary immune response?
IgM, a pentamer that is also the most efficient complement activator and does not cross the placenta.
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