Innate and Adaptive immune system Flashcards
What is the innate immune system
First defence in the body, present at birth but contains no memory and no specificity and responds rapidly.
What are the components of the innate immune system
1a) physical barrier- impermeable outer surface e.g. skin, epithelial cells.
b) cilia in nasal passages and bronchi
c) air borne bacteria are trapped on the mucus by goblet cells.
2) chemical barrier- acidity in the stomach- most pathogens are destroyed by the low pH of the stomach.
b) alkaline secretions
c) lysozyme in tears
3) biological barriers- competition with the commensal organisms
What cells are involved in the innate immunity
phagocytes- moncytes, macrophages, neutrophils
natural killer cells- kill tumour and virally infected cells
eosinophils- attack and kill parasites
What soluble factors are involved in the innate immunity
Lysozyme
complement- involves enzyme cascades
cytokines- particularly interferons
acute phase proteins
What is the adaptive immune system
It is slow, has memory, highly specific, recognises between the self and non-self and is adaptive. It provides immunological memory.
What are the two components of the adaptive immune system?
Humoral component
Cellular component
Explain the two components of the adaptive immune system?
The humoral part has antibodies (immunoglobulins)- which are specific proteins that are produced against a pathogen. It is produced by B lymphocytes that stimulate plasma cells to produce antibodies.
Cellular component allow the recognition of antigens and is medicated by T lymphocytes. They have two components- the helper T cells which help B cells to produce antibodies. Cytotoxic T cells that kill their own cells that have been infected by the virus.
What are the two roles of the immune system?
Recognition- antigen identification
effector- antibody production
What is an antigen?
Antigen- this is any substance that elicits and immune response. The portion that is recognised is epitope or antigenic determinant.
Describe an antibody?
Immunoglobulins have two identical heavy and light chains on each side.
Each heavy/light chain has a variable region towards the top and a constant region at the bottom- The variable region is the N terminus and the constant region is the C terminus.
Both the light and heavy chains are linked by disulphide bridges.
What are the dual functions of antibodies
1) recognition function- binding to the antigen - Fab Arms
2) effector function- Fc molecules will produce effector molecules that will trigger the removal of foreign material.
What are the two types of light chains
Lambda
Kappa
Which globular domains do the light chains fold into
VL (variable light)
CL (constant light)
What does the heavy chain determine?
The heavy chain determines the class of antibody: IgG IgA IgM IgE IgD
What are hypervariable loops/ CDRS?
CDR- complementary determining region
Because they are millions of different antigens, we need a system that can identify these different antigen molecules- if you look at the variable heavy (VH) and variable light (VL) domains- there are 3 areas of intense variability where the amino acid tends to be different from one antibody to another- we refer to these regions as hyper variable loops of CDRs as they form loops in the 3D structure or complementary determining parts which determines which antigen they bind.
CDR- used to determine which antibody binds to which antigen.
Why are CDR’s important
This is because they form the antigen binding site. When the Vh and VL domains are paired, their 6 CDR’s create an antigen binding site. 3 in Vh and 3 in VL
Each antibody will have a slightly different amino acid sequence within each of these hyper-variable loops and these will adopt a different 3D structure for each antibody. Therefore each antibody has its own unique antigen binding site.
Describe IgG
Most abundant in plasma
It is the only IgG class to cross the placenta and protect the child during the early stages of life.
It is the predominant antibody of the secondary response
It triggers complement and phagocytosis via Fc receptors.
4 globular domains
Describe IgM
5 Y shaped units joined by a Joining chain (J) chain and disulphide bridges.
Only in plasma and secretions- molecule is too large to enter tissues.
10 binding sites for antigen- very good at agglutinating particles
very efficient at triggering complement
predominant antibody for primary response
Describe IgA
Main antibody in seromucous secretion- FIRST MILK after baby is born class of antibody first encountered by many invading bacteria and viruses.
What are the subclasses of IgA
IgA1 and IgA2- these are monomeric and dimeric forms
serum IgA- monomeric
secretory IgA- dimeric and has an additional polypeptide (secretory component SC) that protects in harsh environment of secretion
It has 2 different sugar linkage
0 linked
N linked
That protect it from degradation
Describe IgE
It contains 5 globular domains in each of its heavy chains . Lots of N linked oligosaccharides or sugars.
It has an effector function where it interacts with a high affinity receptor. expressed on mast cells and basophils with allergic responses.
Describe IgD
Low concentration in serum
found on lymphocyte surfaces
Effector molecules
Fc receptor are receptors that bind specifically to the Fc region of immunoglobulins.
Fc gamma receptor- IgG
Fc Alpha receptor- IgA
Fc epsalon receptor- IgE
Macrophages- IgG and IgA
Neutrophils- IgA and IgG
Basophils and Mast cells- IgE
What does the binding of antibody-coated targets to the FcR on immune cells can result in
1) phagocytosis
2) release of activated oxygen species
3) release of inflammatory mediators e.g. histamine released from mast cells
4) enhanced antigen presentation
5) clearance of immune complexes
