Immune systems Flashcards
First line of defence
Impermeable barrier
Cell wall
Cuticle
Skin
Mucus
Innate immunity
Found in all animals
In the germ line
Constitutional
Rapid
Non-specific
Do not improve on repeated contact with invading organims
Adaptive immunity
Specific
Slow
Acquired responses not encoded in germ line
specific receptor for each invading organism - selected from randomly created repertoire of receptors
Humoral innate immunity
Anti-microbial peptides (AMPs)
small peptides
broad range of activities against bacteria, protozoa and fungi
make a hole in cell membrane of pathogen
Cellular innate immunity
Hemocytes/macrophages - phagocytic
hemolymph/blood
secretory cells release AMPs
PAMPs
pathogen associated molecular patterns
e.g. peptidoglycan
not found on self cells - only non self
react with PRRs
PRRs
pattern recognition receptors
Gram positive bacteria
Peptidoglycan outer cell wall
Gram negative
Outer membrane around peptidoglycan of LPS
gram stain
purple stain - gram +ive
no stain (stays pink) - gram -ive
AMPs in vertebrates
Humoral
defensins and lysozyme
lysozyme - enzyme that lyzes cells - tears, saliva and mucus
breaks down peptidoglycan - gram +ive
Interferons
Cytokines - cell signalling molecules
active against viruses
Inhibit replication of virus in host cells - direct
Activate antiviral defences of tissue cells - indirect
Activating various effector cells of the immune system such as natural killer cells (NK cells)
Cytokines
Small soluble proteins that function as chemical messengers for immune cells
Pleiotropic - act on different cell types
Redundant - more than one cytokine does the same job
Multi functional - do several jobs
Complement
Heat-inactivated substance in serum needed to ‘complement’ antibacterial action of antibodies in serum
Activation triggers a complex cascade where activation of one component triggers next
Found in all vertebrates/some deuterostomes
Phagocyte action
Move toward pathogen
Make contact
Engulf - forms phagosome
Fusion with lysosome
Release digestive enzymes
kills bacteria
Key features of adaptive immune system
Specificity
Memory
Tolerance to self and harmless antigens
Humoral adaptive response
Antibodies produced by B lymphocytes or B cells
Cellular adaptive response
T lymphocytes or T cells
B lymphocytes
Bursa derived (B) - organ in birds
Produced in bone marrow
Produce immunoglobulins (antibodies)
Antibodies are specific to antigens on surface of pathogens
Complement mediated lysis
Neutralisation of toxins
Aggregation - clumping
Structure of immunoglobulin molecule
Dimeric
2 identical heavy chains
2 identical light chains
Held together by disulphide bonds
Hinge region
Combinatorial diversity
Generation of antibody diversity
Different combinations of heavy and light chains
Rearrangement of gene segments
Junctional diversity
Plasma cells
B cells interact with T helper cells to create
Antibody factories
produce large quantity of specific antibody
Memory B cells
Some plasma cells differentiate into memory B cells
Remember specific antigens so antibodies can be produced rapidly
Classes of mammal immunoglobulins
IgM - pentameric - initial Ig produced during immune response
IgG - main Ig in serum - can cross placenta
IgD - on B cell surface - function unknown
IgA- secreted at mucosal surfaces - 1st line of defence
IgE - parasite infections - allergic responses
