Summary Oxford University FHS revision notes: Immune Response Diversity
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Course
Genetics and Evolution
Institution
Oxford University (OX)
My Oxford University notes for the FHS exam in Genetics and Evolution. Useful for Biology, Biomedical Sciences and Human Sciences. I achieved a first and multiple academic prizes. Includes descriptions of concepts and key references/experiments.
Discuss why two individuals from the same population might respond differently to an infection with the
same pathogen.
Discuss how the patterns of diversity in immune-related genes in extant human populations have emerged
and how they might change in the future.
Inter-population differences
Selection
See notes on Coevolution of Human Pathogens and Human Immunity.
Innate immunity Adaptive immunity
Rapid (0-4 hours) Slower (after 4 days)
Non-specific Specific
Macrophages, neutrophils, dendritic cells T cells and B cells (+ antibody)
No memory Memory (faster response next time)
Diversity of pathogen receptors is in the germline Diversity of pathogen receptors is somatic (not in
(PRRs) the germline)
Innate immunity
Physical barriers to protect against invading pathogens
Enzymes in mucus, tears and saliva
Coughing and sneezing
Cilia in respiratory tract trap foreign material
Intact skin
Mucus and intact mucous membranes (throat and lungs)
Acid in sweat
Acid in stomach
Anti-bacterial proteins and zinc in semen
Competition from commensal bacteria in gut and genital tract
Innate immunity cells
Macrophages
o Large leukocytes (white blood cells)
o Phagocytes (‘eat’ pathogens, cancer cells, cellular debris)
o Play an important role in initiating adaptive immunity
o Found in essentially all tissues
Neutrophils
o Most abundant type of leukocyte in most mammals
, o Phagocytes
o Granulocytes (granules in the cytoplasm which are bactericidal)
o Secrete products that stimulate macrophages
Eosinophils
o Granulocytes
o Important for combatting parasites and helminth infections
o Also, important mediators of allergic responses and asthma
Dendritic cells
o Key as the ‘bridge’ linking innate and adaptive immunity
o Specialised to capture and process pathogen antigens (proteins)
o Present these on their surface to activate cells of the adaptive response
Cytokines and chemokines
Special signalling molecules that coordinate the immune response
Released by lots of different cells
Tell immune cells how to behave e.g. migration, stimulation, function
Example: local inflammation
o Bacteria trigger macrophages to release cytokines and chemokines
o Vasodilation and increased vascular permeability cause redness, heat and swelling
o Inflammatory cells migrate into tissue, releasing inflammatory mediators that cause pain
Adaptive immunity
Adaptive immunity cells
T cells
o Mature in the thymus (hence ‘T’ cells)
o Have a T cell receptor (TCR) on the surface which recognises antigen
o Cellular immune response
o Important in response to intracellular pathogens (HIV, TB)
B cells
o Mature in the bone marrow (hence ‘B’ cells)
o Have a B cell receptor (BCR) on the surface which recognises antigen
o Humoral immune response
o Important in response to extracellular pathogens
Specificity
Each T cell receptor (TCR) or B cell receptor (BCR) has:
o A constant (C) region (anchors it to the cell membrane)
o A variable (V) region (determines antigen specificity)
Each TCR or BCR is specific for one antigen
Around 10 billion different T cells and B cells
But >1015 antigens (so some cross-reactivity) e.g. influenza virus - hepatitis C virus
T cells. Two types:
1) Helper T cells (CD4 co-receptor of TCR)
a. Help the activity of other immune cells by releasing cytokines
b. Can activate other cells, or suppress/regulate immune responses to stop them getting out of
control
2) Cytotoxic T cells (CD8 co-receptor of TCR)
a. Kills infected cells
b. Also kills cancer cells or cells damaged in other ways
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