Lymphocyte activation: B cell Flashcards
What are the phenotypic markers found at the surface of B cells
CD19,CD20,CD21, MHC 2, Surface Ab (IgD/IgM)
T/F: Plasma cells do not have surface Ab
True
Where are most B cells located
In the lymph nodes,MALT, splenic marginal zone
B cell receptor
the antigen recognition unit in the form of membrane bound antibody (Ig), usually IgM or IgD
What is the function of CD21,CD19
CD21 binds opsonized antigenic particles, CD19 is primarily responsible for signal transduction
What are the two ways a B cell can be activated
Thymus-dependent (TD) Antigen, Thymus-Independent(TI) Antigen
What occurs in thymus dependent antigen B cell activation
protein antigen that require activation are guided by the CD4+ Th cells (helper T cell required)
What occurs in thymus independent antigen B cell activation
polymeric Antigen that crosslink the BCR and directly activate the B cell
What are the locations that will determine thymus dependent activation
lymph node germinal center, MALT
What are the location that will determine thymus independent activation
Splenic marginal zone
What are the three signals required for naive B cell activation via thymus dependent antigen
Signal 1: BCR encounters Antigen, Signal 2: costimulatory signal, Signal 3: cytokine signal
How long does it take for a response in thymus dependent antigen activation, how specific are the antibodies
5-15 days, specific for more than just one epitope of a particular antigen
T/F: Only Thymus dependent antigen B cell activation will give rise to memory B cells
True
What happens once a B cell recognizes an antigen as a soluble protein
A protein will bind the B cell receptor causing it to be internalized and digested, Peptides will be joined to MHC 2 and placed on the outside
T/F: Without co-stimulation a helper T cell can still have activity
False: Without co-stimulation there will be nothing that occurs after these interactions
What are the ctyokines that aid a B cell in turning into a plasma cell
IL-4, IL-5
What bond causes the second signal or costimulation in Thymus dependent antigen activation
CD40-L (CD4+) and CD40 (B cell)
What is the other costimulatory pair besides CD40/CD40L, what is the action
B7/CD28, activate the T-cell
How does CD40/CD40L affect the B cell
Promotes up regulation of B7 on B cell, promotes B cell proliferation (clonal expansion), Promotes somatic hypermutation (higher affinity), class switching ( diffrent typers of antibodies made), promote B cell formation
How does CD40/CD40L affect the T cell
Promote T cell to secrete cytokines that will promote growth and antibody production by the activated B-cell
What is needed for a secondary response to occur
The same epitopes must be presented to B and T cells
Why is the secondary response better than the primary responce
higher affinity due to somatic hypermutation -> respond more rapidly -> generate more progeny -> produce higher concentrations of antibodies
How fast is Thymus independent activation, where is it localized
within 2 days,marginal zone of the spleen
T/F: Thymus independent activation causes immunologic memory
False: Thymus independent activation does not create immunologic memory
What are the antibodies created in thymus independent activation, are there other antibodies created
IgM, no
What are the two types of Thymus independent antigen activation
Type 1:Mitogens activate multiple different B cell clones to produce antibodies (polyclonal response), Type 2: multiple and repeating identical epitopes
What are the signals that occur in Type 1 (mitogen) Thymus independent activation
1st signal: BCR binds polymeric Antigen (mitogen binds but NON-SPECIFICALLY) 2nd signal: Toll like recpetors respond to the mitogen
What is the result of Type 1 (mitogen) thymus independent activation
Pattern recognition receptor on the B cell leads to cell division and antibody production
What are the signals that occur in Type 2 (repeating BCR) thymus independent activation
1st signal: BCR binds antigen with repeating identical epitopes 2nd signal: provided by clustering of BCRs
What are the type of antigens that cause Type 1 thymus independent activation, type 2
Type 1: lipopolysachrides derived from cell walls and protein coats of viruses, Type 2: bacterial flagelin, bacterial and fungal polysachrides, nucleic acids
What is the key difference between type 1 and type 2
Type 1 can activate multiple B cells leading to polycloncal activation of B cells
What are key features of Thymus independent antigen activation
Essention in recognition of non-protien antigens, generate primarliy low affinity IgM antibodies (no class switching and no somatic hypermutation), not developed until 2nd year of life
What are the three key transcription factors in intracellular signalling pathway after thymus dependent activation, what are the results
NFAT, NFkB, AP-1, proliferation/synthesis of Ig/cytokine receptors
What are the maturation events in thymus dependent antigen activation
class switching, somatic hypermutation, differentiation into antibody producing plasma cell or memory B cell
T/F: Maturation events occur in both thymus dependent antigen activation and thymus independent antigen activation
False: Maturation events only occur in thymus dependent antigen activation
What are the antibodies that cause aggultination, complement activation
IgG/IgM/IgA, IgG/IgM
What are the five steps of the hummoral immunity
1) Inactivation of viruses and neturilizations of bacterial toxins 2) Cells clump or agglutinate 3) Ag-Ab complex formation leads to complement fixation 4) macrophages have enhanced phagocytosis due to Fc receptors 5) Destruction by non specific immune cells
What percentage of B lymphocytes circulates
10-15%
