BIO 304 · Human Anatomy & Physiology
Adaptive Immunity
Lymphatic & Immune · Module 12
A reference for the Adaptive Immunity video. The adaptive immune system has specificity and memory. It uses T cells to handle intracellular threats and B cells to make antibodies against extracellular ones.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet , print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice; type the term, click Reveal to check yourself.
- Compare humoral and cell-mediated immunity by primary effector cell, target, and mechanism.
- List the five immunoglobulin classes and the role of each.
- Distinguish primary from secondary antibody response and explain immunologic memory.
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T Cells
Origin & selection
- Born in bone marrowmigrate to thymus to mature
- Positive selectionmust recognize self-MHC
- Negative selectionmust not react too strongly to self-peptide
- TCR (T-cell receptor)binds antigen + MHC; one specificity per cell
Major T-cell subsets
- CD4+ helper T (Tʈ)recognizes antigen on MHC II (APCs); orchestrates response
- CD8+ cytotoxic T (Tʌ)recognizes antigen on MHC I (all nucleated cells); kills infected/tumor cells
- Regulatory T (Tʀɐɡ)suppresses immune responses; prevents autoimmunity
- Memory T cellspersist after infection; fast response on re-exposure
MHC presentation
- MHC Ion all nucleated cells; presents endogenous (intracellular) antigen to CD8+
- MHC IIon antigen-presenting cells; presents exogenous (engulfed) antigen to CD4+
Cytotoxic T mechanisms
- Perforin + granzymespokes holes; triggers apoptosis
- Fas-FasLdeath receptor pathway
- Targetvirus-infected cells, tumor cells, transplant cells
B Cells & Antibodies
B-cell activation
- BCR (B-cell receptor)membrane antibody; binds antigen directly
- T-dependent activationantigen + helper T cell signal → full response
- Clonal expansionactivated B cell divides; daughter cells differentiate
- Plasma cellantibody factory; lives days to weeks
- Memory B celllong-lived; ready for re-exposure
Five antibody classes
- IgGmost abundant in serum; crosses placenta; secondary response dominant
- IgAmucosal & secretions (tears, saliva, breast milk); dimer
- IgMfirst antibody made in primary response; pentamer; great agglutinator
- IgEallergy & parasites; binds mast cells
- IgDBCR; function poorly understood
How antibodies neutralize threats
- Neutralizationblocks pathogen binding sites
- Opsonizationtags pathogen for phagocytes
- Agglutinationclumps pathogens together
- Precipitationsoluble antigens clumped out of solution
- Complement activationtriggers complement cascade
Primary vs secondary response
- Primary responsefirst exposure; latency 5-10 days; IgM dominant; modest titer
- Secondary responsesubsequent exposure; latency 1-3 days; IgG dominant; high titer
- Memory cellsare why this works; ready and waiting
- Vaccinationsafely creates a primary response so the next exposure is the easier secondary
Active vs passive immunity
- Active naturalinfection → you make your own antibodies
- Active artificialvaccination
- Passive naturalmaternal antibodies (IgG transplacental, IgA breast milk)
- Passive artificialdonor antibodies (RhoGAM, antivenin, IVIG); short-lived
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