Pathology Cheat Sheet
Protection Needs Restraint
Innate and adaptive immunity for NEET-PG: pattern recognition receptors, T and B cells, MHC class I vs II, complement pathways, and co-stimulation signals.
MedNext Academy | 3 min read
Clinically reviewed by Dr Shameer Deen, MBBS, MS, MRCS
Protection Needs Restraint
Innate and adaptive immunity for NEET-PG: pattern recognition receptors, T and B cells, MHC class I vs II, complement pathways, and co-stimulation signals.
The principles and mechanisms of innate and adaptive immunity, including the cells, receptors, and complement pathways.
High-yield lines
- Innate immunity is the rapid non-specific first line of defence using germline-encoded pattern recognition receptors.
- Toll-like receptors recognise pathogen-associated molecular patterns such as lipopolysaccharide and viral RNA.
- Adaptive immunity is antigen-specific, generates memory, and is mediated by T and B lymphocytes.
- V(D)J recombination generates the enormous diversity of T-cell and B-cell receptors.
- CD8 cytotoxic T cells kill infected or tumour cells using perforin and granzyme B or the Fas pathway.
- CD4 helper T cells orchestrate immunity through cytokines and differentiate into Th1, Th2, Th17, Tfh, and regulatory subsets.
- Regulatory T cells expressing FoxP3 maintain peripheral tolerance, and FoxP3 mutation causes IPEX syndrome.
- Natural killer cells kill cells with low MHC class I (missing self) and mediate antibody-dependent cytotoxicity through CD16.
- MHC class I presents endogenous peptides to CD8 T cells, while MHC class II presents exogenous peptides to CD4 T cells.
- The complement system is activated by classical, lectin, and alternative pathways that all converge on cleaving C3.
- C3a and C5a are anaphylatoxins, C3b is an opsonin, and C5b to C9 form the membrane attack complex.
- T-cell activation requires signal 1 through the T-cell receptor and signal 2 co-stimulation through CD28 binding B7, otherwise anergy results.
Mapped competency codes
- PA9.1
Continue into the full chapter
This summary maps to PA9-immunopathology-and-aids.
Frequently Asked Questions
How do innate and adaptive immunity differ?
Innate immunity is rapid and non-specific using pattern recognition receptors, while adaptive immunity is antigen-specific, slower to develop, and generates lasting immunological memory.
What do MHC class I and class II molecules present?
MHC class I presents endogenous peptides to CD8 cytotoxic T cells, while MHC class II presents exogenous peptides to CD4 helper T cells.
How do natural killer cells recognise their targets?
They kill cells that have lost MHC class I expression, the missing-self mechanism, and also mediate antibody-dependent cellular cytotoxicity through the CD16 receptor.
Why are two signals needed for T-cell activation?
Signal 1 through the T-cell receptor plus signal 2 co-stimulation through CD28 binding B7 activates the cell, while signal 1 alone induces anergy, which supports peripheral tolerance.
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