Lymphocytes Flashcards
3 types of B cells
Naive B cells
Memory B cells
Plasma cells
What are Naive B cells?
- Circulating B cells which, when activated, initiate the germinal centre response
What are memory B cells?
dormant B cells that arise from B cell differentiation and initiate a stronger, more rapid antibody response
What are plasma cells?
Terminally differentiated B cells which contain abundant antibodies
What are cytotoxic T cells?
T cells which express CD8 and recognise antigens associated with MHC class I molecules. They are capable of destroying virally infected or allogenic cells
What do cytotoxic T cells do?
1) Cytotoxic T cell binds to infected cell
2) Perforin makes holes in infected cells membrane and enzyme enters
3) Infected cell is destroyed
What are helper T cells?
T cells which express CD4 and recognise antigens associated with MHC class II molecules
Subtypes of Helper T cells
- Helping b cells to divide, differentiate and secrete antibodies
- 4 types of T cells produced (T-helper cell subsets)
- Activating macrophages to destroy pathogens that they have phagocytosed
- Recruiting cells to site of inflammation
4 T helper cell subtypes
Th1
Th2
Th17
Treg
B cell activation
-B lymphocyte activation is initiated by the binding of antigens to B cell receptor
- B cells presenting antigens (MHC II) are recognised by Th2 cells
- With appropriate support from T cells and the microenvironment of germinal centres, these B cells proliferate and differentiate into plasma cells and memory B cells
11 features of lymph node structure
- Primary lymphoid follicle (mostly B cells)
- Paracortical area (mostly T cells)
- Medullary cord (macrophages and plasma cells)
- Medullary sinus
- Efferent lymphatic vessel
- Blood vessels
- Secondary lymphoid follicle (with germinal center)
- Marginal sinus
- Germinal center
- Afferent lymphatic vessel
- Cortical sinus
What 3 parts does the germinal centre response include
- Clonal expansion
- Somatic hypermutation
- Class switching
What is clonal expansion?
The process by which a B cell proliferates into centroblasts. This takes place within a germinal centre’s dark zone
What is somatic hypermutation?
The process by which mutations are introduced into centroblasts. This facilitated by an enzyme called AID and leads to subtle changes to the b cell antibody
What is class switching?
the process by which antibodies change type
4 parts of an antibody
- Light chain
- Heavy chain
- Variable region
- Constant region
What is the variable region of an antibody?
Change the peptide sequence
able to recognise different antigens
Fab & Fc
Fab= antigen binding
Fc= biological activity mediation
VDJ recombination
- A process which takes place during B cell development which allows them to generate a massively diverse range of receptors
- Variable region gene fragments (65)
- Diverse gene fragment (27)
- Joint gene fragments (6)
10,530 types of antibodies can be produced
What are the 5 different types of antibodies
IgG
IgA
IgM
IgD
IgE
IgG
- Most abundant antibody
- 3 types IgG1, IgG2, IgG3
- Serves as an opsonin (helps phagocytes hold on to bacteria)
- Activates the classical complement pathway and works with NK cells to allow the NK cells to kill virally infected cells
- The only antibody that can cross the placenta
IgA
- 2 types= IgA1 & IgA2
- Serves as opsonin for eosinophils, neutrophils & macrophages
- Cannot cross the placenta and does not activate complement
- The main immunoglobin found in mucosal sites, binds to pathogens and encourages them to be disposed of in various ways
- Babies receive IgA in breast milk
IgM
- First antibody response made, made without T helper cells
- Most effective at activating the complement pathway
- Two types:
- pentamer held together by a J chain
- B cell receptor
IgD
- Found in mature B lymphocytes
- Serves as a signal that mature B lymphocytes are ready to leave the bone marrow
IgE
- Associated with allergic and anti parasitic responses
- Binds to receptors on mast cells, basophils and eosinophils, when this happens, these cells release cytotoxic granules
- Sometimes, IgE is made inappropriately to certain non- pathogenic targets
What happens in primary immune response?
1st infection
Naive B cells
Activated B cells formed
Short lived plasma cells in lymphoid organs
IgG
IgM
Low level antibody production
Long lived plasma cells in the bone marrow
What happens in secondary immune response?
Repeat infection
Memory B cells
Plasma cells
IgG
Long lived plasma cells in bone marrow
Memory B cell
What are major histocompatibility complex molecules?
They are the proteins on the surface of APC that do the ‘presenting’ of the antigens.
MHC class I molecules features
3 alpha
1x beta-2- microglobulin
- Found on all nucleated cells and platelets
- Bound by CD8 molecules on cytotoxic T cells
- Displays peptide fragments of proteins from within the cell
- Any cell that displays abnormal peptides will activate cytotoxic T cells
MHC Class II molecules
2x alpha
2x beta
- Found on B cells, macrophages, monocytes, APC and some T cells
- Bound by CD4 molecules on helper T cells
- Displays antigens derived from extracellular proteins which have been acquired through phagocytosis
What is tolerance?
Tolerance is a specific immune non- reactivity against certain antigens (e.g. cell antigens)
- Clonal deletion: B & T cells which are in the process of maturing and found to have receptors to “self” antigens are destroyed before they finish maturing
What is anergy?
Anergy occurs when the immune system is unable to mount a normal immune response against a specific antigen
- B & T cells become “frozen” and unable to activate
