S1: Adaptive Immunity I Flashcards
Name the 3 stages unseen infections progress through
- Initial infection which stimulates an immune response. This can be innate (no memory) and adaptive (acquired) which has memory
- Recovery due to immune activity
- Lasting acquired immunity is specific and often for life
What is the innate immune system?
- it is rapid and non specific
- often fails to completely eliminate the infection but is crucial in keeping an individual alive for the first few days of infection
What are the cellular and humoral components of the innate immune system?
- Cellular: phagocytes and natural killer cells (NK) cells
2. Humoral: complement, pattern receptors, enzymes and cytokines
What is the adaptive immune system?
- it has a delayed response and is highly specific
- usually eliminates the infection
- it has ‘memory’ whereby if the same antigens appears, the body with recognise it very quickly. This response the repeated infection gives long term immunity.
What are the cellular and humoral components of the adaptive immune system?
- Cellular (T cells): T helper (Th) regulation, Cytotoxic (CTL), regulatory (Treg) and cytokines
- Humoral (B cells): antibodies
Explain the difference in primary response and secondary response of the adaptive immune system
At first exposure to infection, the response to the adaptive immune system will be delayed and relatively small (little antibodies produced)
Upon the second exposure with the same microbe there is an immediate response that is much greater (large antibody concentration in less time)
What are antibodies?
Antibodies are glycoproteins that are also called immunoglobulin (Ig)
- Each antibody binds to a specific antigen (which is most often a protein, but can be glycolipids)
What happens if you take serum and do a serum electrophoresis?
The antibodies will migrate in the y-globulin fraction (band). It is a widespread band as there is a mixture of different antibodies.
Describe the structure of the basic antibody
- two identical antigen binding sites per Ig molecule
- a ‘hinge’ H region is a flexible spacer between blood bring sites
- structure is tetrameric protein: 2 identical heavy chains and 2 identical light chains.
- The 4 polypeptide chains are bound by disulphide covalent bonds between cysteine a.a. Residues into a Y shaped molecules
- folding of the antibody is the tertiary structure because it is a heavy and light chain joined
- overall structure is the antibody is quaternary
What 2 genes code for light chain?
It’s either Kappa or Lambda!
Never both
What determines the type of Ig made?
Genes determine the type of heavy chain and therefore Fc region which determine the type of Ig made
What is ‘fraction antigen binding’ (Fab)?
Each chain has a variable region (including heavy and light chain) where the sequence varies from one Ig molecule to another.
The variable sequence called Fab binds to the antigen
- Fab are crystallisable
What is the constant region (Fc)?
Fc also stands for fraction crystalline
This is responsible for the effector functions of the antibody e.g. activating complement, binding to phagocytes
-phagocytes have proteins called Fc receptors on their cell surface so they recognise the antibodies and what they are bound to —> opsonisation
Name the different classes of Ig
IgA (2 isotopes) IgD IgE IgG (4 isotopes) IgM
What is the major Ig class in circulation (75% of all Ig)?
IgG
What is the major class of Ig made by secondary responses?
IgG
Function of IgG
- It is very good at activating the complement system via classical pathway (removing the pathogen) as the complement system needs antibody to bind to antigen for it to work
- it acts as an opsonin (identify and move item) —> Ig binds to pathogen —> phagocytes recognise IgG via their Fc factors which bind to Fc receptors on phagocyte —> phagocytose the pathogen
Which is IgG essential in pregnant mothers?
It is the only class of antibody that is small enough to cross the placenta and protect the developing foetus
What can be suggested of IgG being present for long periods in serum?
IgG antibodies may indicate last exposure and no current infection