what are B cells?
communicate with T cells, have specific B cell receptor for antigens, produce antibodies
what is clonal expansion?
generation of 2 subsets
what ae plasma cells
large antibody factories
what are memory B cells?
mount a quicker antibody response to any subsequent infections
where do you find B cells?
mature in bone marrow, circulate in blood and lymph and are found in large numbers in lymphoid organs
how do B cells recognize antigens?
through B Cell Receptor which is actual antibody - diversity
what do b cells become once activated
plasma cells
what are the 5 types of immunoglobulins produces by b cells (as receptors)
IgG, IgE, IgD, IgM, IgA
describe b cell receptor structure
different to t cells, but has variable and constant regions, and light and heavy chains
what are the 3 main functions of antibodies?
neutralization, opsonization, initiation of complement
what is the goal of antibodies?
prevent microbial activity and aid removal of threat from host
what is opsonisation?
coating of pathogens by antibodies or complement proteins; phagocytosis, antibody dependent cellular cytotoxicity, mast cell degranulation
describe b cell development
each development stage is defines by rearrangements of the immunoglobulin heavy and light chain genes, once in periphery b cells migrate to secondary lymphoid organs
what are the components of heavy chain?
variable, diversity and joining genes
what are the components of light chain?
variable and joining genes
what immunoglobulins do immature and mature b cells express?
immature = IgM mature = IgM and IgD
how do b cells undergo negative selection?
macrophages engulf and remove self- reacting b cells
what are the 2 types of b cell activation?
thymus-dependent
antigens which don’t require t cell help
thymus-independent
antigens which dont
describe b cell activation
occurs n lymph nodes
activation of naïve b cell results in rise of plasma cells
describe thymus-dependent activation
co-receptor binding, cytokine signals released from t helper cells induce proliferation
generates pool of plasma cells which produce antibody
also generates memory b cells
plasma cells initially produce IgM
describe thymus-independent activation
certain antigens can activate directly, cells differentiate into plasma and produce IgM but antibody response weaker than antigen dependant b cell activation, doesn’t lead to generation of memory cells
what is class switching?
caused by class switching, IgM response is weak, cells class switch to IgG, occurs by gene rearrangement, but antigen binding site remains same, antibody has increasing affinity for antigen
what is avidity?
ability of antibodies to form complexes
what is cross talk?
in lymphoid organs, between B and T cells, leads to generation of both humoral and cellular immune response
what are germinal centres?
hubs for t and b cross talk, also proliferation, differentiation, somatic hypermutation-class switching
describe the vaccination process
in primary immune response IgM acts early but as b cells undergo class switching an IgG response follows, presence of memory t and b cells means on 2nd exposure immune system responds much faster, cells also primed to produce more effective IgG response immediately
what is immunological tolerance?
an active response to a particular antigen-central and peripheral
what is central tolerance
in primary lymphoid organs- thymus for t and bone marrow for b, + and - selection eliminates >90% of t cells
what is peripheral tolerance (t cells)
not all self reactive t cells are eliminated, however peripheral tolerance prevents their activation
signal 1, no signal 2 =
anergy
signal 1 + 2 no 3 =
deletion by apoptosis
what can Treg cells do in peripheral tolerance?
directly block activity by binding antigen
what is peripheral tolerance (in b cells)
occurs in secondary lymphoid organs, self reactive b cells still require help from self reactive t cells, since most eliminated the b cells become anergic
what is breach of tolerance?
to self antigens or commensal organisms drived many autoimmune diseases