b cells and antibodies Flashcards
What is part of the ‘adaptive’ immune system?
antibodies and T cells
What part of antigens do antibodies actually recognise?
epitopes
What does the Fc region of antibodies do?
interacts with other cells and molecules of the immune system
What are the 5 antibody isotypes?
- IgM
- IgD
- IgA
- IgG
- IgE
Describe the IgM response?
- first antibody produced in immune response
- low affinity for antigen
- forms ‘pentamers’, held together by joining (j) chain
Describe IgA
- only antibody that can cross mucosal surfaces
- found in secretions (colostrum rich in this)
- protected from digestion by secretory component (s chain)
- forms dimers (joining j chain)
Describe IgD
- like IgM, first antibody produced by B cell
- but no known function
Describe IgG
- main mature antibody form
- circulates as a monomer
Describe IgE
- circulates as monomer
- exact function not known (believed to be important for parasitic infection)
- defo important in allergic disease
What are the 3 ways antibodies can help us?
- by binding to things and affecting them
- by binding to things and interacting with another element of the immune system
- when bound to b cells: act as receptors
What are the ways antibodies can bind to things and affect them?
- toxin neutralisation
- receptor blocking
What are the ways antibodies can bind to things and interact with another element of the immune system?
- phagocytes (opsonisation)
- mast cell activation
- complement
- antibody-dependent cellular cytotoxicity
How do antibodies aid in opsonisation?
- bacteria coated by antibody
- phagocytic cells have receptors for Fc portion of antibody
- enhances phagocytosis by reducing repulsion between two negatively charged membranes
How do antibodies aid in mast cell activation?
- mast cells coated with IgE antibody (has Fc receptor)
- when appropriate antigen binds IgE antibodies, mast cell ‘degranulates’, releasing histamine
How do antibodies aid in antibody-dependent cellular toxicity?
- NK cell recognises antibody-coated bacteria by Fc receptor
- target organism then killed by non-phagocytic means
How do antibodies aid in interaction with ‘complement’?
activates complement system:
1. opsonisation
2. inflammation
3. terminal attack pathway
What is the principle of receptor generation by somatic recombination
select gene segment from region 1, 2 and 3 at random and combine them to make variable region of antibody
What is clonal selection?
division and selection of the fittest B cells
What are the two things B cells do when they divide?
- class switch
- somatic hypermutation
What is the class switch that happens during B cell divison?
- IgM in primary response switches to IgG
- variable region of antibody remains the same though
What is somatic hypermutation that happens during B cell divison?
- random mutations introduced into variable region
- daughter cells therefore produce slightly different antibody
- further clonal selection pick out best receptors
What is the primary immune response?
- low affinity IgM antibody meets antibody
- class switch or somatic hypermutation
What is the secondary immune response?
- best B cells now selected and number increased
- these mature B cells become memory cells and respond vigorously when stimulated again (a lot of IgG)
