Lecture 22: Cellular Interactions and Trafficking - B cells Flashcards
Following development, what can B cells mature into?
B-1 B cells and B-2 B cells which can differentiate into follicular or marginal zone B-2 B cells
What are characteristics of B-1 B cells?
progenitors distinct from B-2 B cells
mostly recognise capsular polysaccharide antigens
able to produce IgM without T cell help
What are the different types of B-2 B cells?
marginal zone, follicular and memory B cells
Why is there continual competition for entry of B-2 B cells?
due to limited number of follicles which favour established B cells
Where are marginal zone B cells found?
in the marginal zones of the white pulp
What is the role of marginal zone B cells?
poised to make rapid responses to blood-borne antigens
relatively broad specificity
What responses do marginal zone B cells produce?
typically T cell independent responses and does not generate memory
What are follicular B cells and what do they express?
form the majority of B cells and are involved in the co-expression of IgM and IgD
What are follicular B cells capable of? What is their activation threshold like?
recirculating through lymphoid tissues
higher activation threshold for proliferation and differentiation
What is the role of memory B cells?
rapid response to re-encounters
Why are memory B cells usually less differentiated?
so they have the ability to refine Ab affinity
What is the role of B cell responses?
antibody secretion to protect from extracellular pathogens and toxins
What are antibodies involved in?
neutralisation, opsonisation and complement activation
What do B cell responses require in order to be activated?
require activation of naive B cells
require multiple signals
When do T cell independent responses occur?
typically with highly repetitive molecules such as polysaccharides of bacterial cell walls
What do T cell independent responses involve?
activation of B cells without T cell help
activated by the cross linking of BCRs
What are T cell independent responses normally limited to?
usually limited to IgM but cytokines may enhance response
What is required for the activation of T cell dependent responses?
require multiple signals to induce efficient responses
dependent on CD40/CD40L interaction between B cells and Tfh
What is important in maintenance of self-tolerance?
both CD4 T cells and B cells have to to be activated during a T cell response
How are antigens detected by B cells?
native antigen can passively drain through lymphatics
key roles for other cell types in active presentation e.g. subcapsular macrophages and follicular dendritic cells
Where are subcapsular macrophages found?
in subcapsular sinus of LNs and marginal sinus of the spleen
What is the role of subscapular macrophages?
able to take up antigen but does not degrade them
decorates the surface with antigen
What are follicular dendritic cells and where are they found?
not dendritic cells but stromal cells which are found embedded throughout the follicles
What type of cell are follicular dendritic cells?
non-phagocytic cell of non-hematopoietic origin
