Immunology- Introduction to B cells and antibodies Flashcards
What are the specific antibodies involved in humoral immunity?
IgD IgM IgG IgA IgE
What does IgD do?
Antigen receptor virgin B-cells
What does IgM do?
Agglutinin; activates complement
What does IgG do?
Opsonin; activates complement
What does IgA do?
Secretory; protects mucosa
What does IgE do?
Inflammatory; protection vs helminths
Define the non-specific movements in humoral immunity?
Complements Cytolysis Chemotaxis Inflammation Opsonisation
How do B cells respond to antigens?
The stay within the lymphatic tissue and respond to antigens by differentiating into plasma cells.
Explain the activation of B cells?
B cells are activated by B cell receptors which bind to specific antigens
B cells in lymphatic tissues respond to either unprocessed antigens or antigens presented on a APC.
How do B cells respond to a foreign antigen?
They initially respond to foreign antigens by taking in some of the antigens molecules and combining the antigen fragments to an MHC 2.
This complex is then recognised by helper t-cells allowing the realise of cytokines such as IL-2 IL-4 and IL-6.
These co stimulate B cells and activates them allowing differentiation into plasma cells which secrets antibodies to a specific antigen. Some do not differentiate into a plasma cells they will sometimes differentiate into a memory cells.
What components are antibodies made up of?
2 identical heavy chain made up f 450 amino acids
2 identical light chains made up of 220 amino acids.
The 2 light chain are bonded to the heavy chains via disulphide bridges.
The 2 heavy chains are also joined together via disulphide bonds which forms a hinge.
What are the 2 antibody regions?
Constant region
Variable region
What is significant about the variable region of an antibody?
It is specific on every antibody as it needs to be complimentary to the antigen.
How many isotopes does the antibody have?
5
Name the 5 antibody isotopes?
IgG IgE IgA IgM IgD
What are the 3 ways antibodies target antigens via antibody-antigen binding?
Agglutination- where antibodies form cross linkages to form clumps.
Neutralisation- antibody covers the biologically active form of a microbe or toxin.
Precipitation- Forms cross linkages forming insoluble antigen antibody complex
Name the 3 ways the Fc portion of the antibody bind to target cells?
Complement fixation- Fc region binds to complement protein and complement system becomes activated.
Opsonisation- Fc region binds to receptors on the phagocytic cells activating phagocytosis.
Activation of NK cells- Fc region binds to NK cells triggering release of cytotoxins.
What are the complement proteins
C1-C9
What are the complement factors?
Factor B; Factor D; Properdin
What are the complement receptors?
Complement receptors [CR] CR1; CR2; CR3
What are the 3 complement pathways?
- Alternative Pathway (innate)
- Classical pathways
- Lectin pathways
Explain the mechanism of the classical complement pathway?
- Antibody [IgM or IgG] binds to epitopes of antigen
- C1 binds to Fc region of antibodies
- C1r activates C1s which is a proteinase
- C1s cleaves C4
- C4b binds to antigen; C4a remains in fluid phase
- C1s cleaves C2
- C2b binds to antigen; C2a remains in fluid phase
- C2b is a proteinase which cleaves C3
- C3b binds to antigen; C3a remains in fluid phase
- C2b cleaves C5
- C5b does not spontaneously bind; C5a in fluid phase
- C5b does not spontaneously bind; C5a in fluid phase
- C5b678 binds to the lipid bi-layer
- C9 [pore forming protein] inserts hole into the membrane
- Microorganism is lysed by the membrane attack complex
What is the function of the membrane attack complex?
Forms pores in lipid bi-layer membranes of microorganisms
Which bacteria does MAC destroy and which one does it not?
Kills Gram-negative bacteria, enveloped viruses and some protozoan parasites
Gram positive bacteria protect themselves from complement mediated lysis by their thick peptidoglycan cell walls
Fungi protect themselves from complement mediated lysis by their thick chitin cell walls
what is the function of C3a and C5a?
Although gram +ve bacteria can not be killed it can try to eliminate it from the body.
C3a and C5a are “anaphylatoxins” they activate mast cellsC3a and C5a are chemotaxins.
They attract phagocytes (neutrophils and mononuclear pahgocytes)C3b is an opsonin; it enables phagocytes to recognise and bind to antigens and phagocytose them
How does the alternative pathway work?
Doesn’t involve antibodies - innate immunityInteractions between microbial surface polysaccharides and factors B, D and P. this interaction then activates complement protein C3, which in turn activates the enzyme cascade
What occurs if the same antigen infects the body again. How does the immune system respond?
After contact with a new antigen there is a steadily increases in the antibody titer, first IgM, then IgG, this antibody titre then steadily decreases.
The initial contact with an antigen is called the primary response. If the antigen is encountered a second time the memory cells become activated – the secondary response.In the secondary response, the memory cells quickly proliferate and produce vast quantities of mostly IgG antibodies.
Immunological memory provides the basis if vaccination.
Does the immune response remain the same in an ageing individual. If not why?
As individuals age they tend to become more susceptible to infectious diseases. This is mostly associated with lower levels of immune function. For example T cells become less responsive to antigens, and fewer T cells respond to infections. This may arise because of age related atrophy of the thymus, or decreased production of thymic hormones. Associated with the decrease in the numbers of t cells is a decrease in the number of b cells , so the antibody titre does not increase as rapidly in older individuals. Thus vaccinations against influenza are provided every year for older individuals.
