Immunology: Initiation of Acquired Immune Responses - B Cells Flashcards
where do
- B cells
- T cells
mature
- bone marrow
- thymus
what immune response are
- B cells
- T cells
responsible for
- humoral
- cellular
what is the role of B cells
- produce antibodies to attack pathogens in circulation
- defend against both EC and IC pathogens
what is the role of T cells
- defend against IC pathogens
what do CD4+ T cells do
- T helper cells
- regulate immune system
what do CD8+ T cells do
- cytotoxic T cells
- kill virally infected host cells
give a general description of antibodies
- bind to a specific antigen
- complex of 4 polypeptide chains
- unique variable region that binds to antigens (Fc)
how do B cells use antibodies
membrane bound antibodies - receptor to reg=cognise and bind to antigens
why is the B and T cell response more specific to antigens
they express 1 antigen receptors that binds to a specific antigen epitope
where are mature T and B cells usually
circulating between blood, lymph and 2* lymphoid tissue
how to T and B cells enter lymph nodes
via high endothelial venules (HEV)
what is the function of lymph nodes
- key site of pathogen detection
- faciliate T and B cell activation
what happens once
- B cells
- T cells
enter lymph nodes
- go to lymphoid follicle
- go to T cell area and interact with dendritic cells
how do denritic cells enter lymph nodes
via lymph
how do lymph and lymphocytes leave the lymph nodes and where to they go after
- leave through the medullary sinus then into lymph vessels
- eventually drains into a subclavian vein
what 2 types of cells do B cells differentiate into once activated
- plamsa B cells
- memory B cells
what is the role of plasma B cells
produce and secrete soluble antibodies
what is the role of memory B cells
long-lived and continually circulate after infection
what antibodies do B cells use to respond to specific antigens
membrane-bound Igd/IgG
describe how B cells encounter antigens
- soluble antigens are released into tissues as debris after phagocytosis
- they then travel to lymph nodes and are trapped by cells expressing opsonin receptors
- B cells encounter them and activate
what are opsonised antigens
antigens released into tissues after phagocytosis
what do B cells need to activate
- antigen
- ‘helping’ signal
what are the 2 signals B cells need to activate in
- protein antigens
- other antigens
- repetitive epitopes
- BCR binding and Th cell help
- BCR + antigen and PRRs + PAMPs
- multiple BCRs + antigens engaged
after actviation what happens to B cells
clonally proliferate forming a germinal centre, can then differentiate
what do plasma cells initially secrete
IgM
B cells start producing ‘better’ antibodies (i.e. IgG, IgA, etc) with help from what
T helper cells presenting antigens to B cells
what is the recognition function of Igs in killing pathogens
bind to antigen mediated by variable region sites
what is the effector function of Igs in killing pathogens
clearance mechanisms that are mediated by the interaction of the heavy chain constant region with effector molecules (Fc receptors, complement proteins)
what is the functin of IgM in its membrane bound form and what form is it in
- activates B cells
- monomer
what is the functin of IgM in its secreted form and what form is it in
- agglutination and complement activation
- pentamer
what is agglutination and what mediates it
- antibody cross-links multiple antigens produing antigen clumps
- IgM/IgG
what is the function of agglutination and why
- enhances phagocytosis
- many antigens phagocytosed at once
what region of IgM/IgG activated the complement system and how does this work
- Fc region (when bound to antigens)
- Fc binds to antigen and a conformational change occurs, this exposes multiple binding site for the first intermediate of the classical pathway
which antibody is the most abundant
IgG
which antibody is the most dominant in the 2* immune response
IgG
what form is IgG in and what is its functions
- monomeric
- agglutination, NK activation, opsonisation, complement activation, neutralisation, foetal immune protection
what is IgG’s role in foetal immune protection
- transported across then placenta into foetal circulation
- protects neonates against pathogens until it develops its own immune system
what can lead to low levels if IgG in neonates
IgG levels from the mother wanes over time and therefore without its own production leading to low levels
what is neutralisation and what mediates it
- prevents viruses infecting host cells and microbial toxins disrupting normal cell functions
- IgG and secretory IgA
how does neutralisation perform its functions
- block entry of toxins/viruses into cell
- cause agglutination of viral particles
- stop uncoating of viral genomes
- interfere with viruses binding to receptors
what antibody is a good opsonin and why
- IgG
- phagocytes possess and Fc receptor that IgG binds to, enhancing phagocytosis
how are NK cells activated in the innate immune system
- pathogens recognised by PAMPs
- interferons secreted
- NK cells activated
how are NK cells activated in the adaptive immune system
- IgG secreted
- NK cells activated
how do NK cells kill virally-infected host cells
via pro-inflammatory mediators
what is the function of IgD and what form is it in
- B cell activation, membrane bound B cell receptor
- monomer
what antibody is the second most abundant
IgA
what 2 forms does IgA come in and what are each of their functions
- monomer in serum, neutralisation
- dimer in secretory fluids (SIgA), neonatal defence and neutralisation
how does IgA provide neonatal defence
transported into colostum and breast milks to protect neonatal GI tract
what does IgE trigger
allergic responses
