Adaptive Immunity-08 Flashcards
what are the hallmark features of adaptive responses?
memory and specificity
somatic recombination
DNA segments shuffled and form new combinations of base sequences to produce antibody genes; can generate BCRs and TCRs
BCRs and TCRs
2 Types of antigen receptors that recognize specific antigenic determinants
how quick-acting is the adaptive response?
slow; 3-5 days
in which is the adaptive immune response present?
only in jawed vertebrates
adaptive response and specificity
narrow specificity and huge specificity repertoire
what happens when a vaccine is administered?
a dendritic cell picks it up and takes it to the lymph node; B-cell that recognizes it will make multiple copies of itself and become plasma cells producing antibodies against that vaccine
transition from innate to adaptive response
performed when APCs interact with a T-cell that is specific for a given antigen; they are capable of taking something from outside the cell, bringing it into the cell and presenting it up on the surface w/ MHCII to show to other immune cells (make antibodies)
what is an antigen?
any molecule to which an antibody can specifically bind; proteins, carbohydrates, nucleic acids, etc
antibody (Ab)
a globular protein produced by B cells that can bind to a specific antigen; when an Ab binds to its antigen, it tags toe pathogen for destruction by phagocytes like macrophages and neutrophils; antibodies = immunoglobulins
MHC I
is expressed on almost all nucleated cells
MHC II
only expressed on professional APCs
what can T cells recognize?
T cells only recognize fragments of antigenic proteins that are processed and presented in a certain way - they can’t recognize “native” antigen
role of antigen-presenting cells
pick up the antigen, process it and present it on MHC proteins
what are the antigen processing pathways?
MHCI & MHCII
MHC I pathway
for stuff you already make inside your cells
- pathogen goes through ER and is put to MHC and inserted onto plasma membrane
- passing T cells detect infection by unfamiliar virus
- excites CD8+ or cytotoxic T cell
MHC II pathway
extracellular pathogens
- professional APC takes something from outside into it and processes it through a lysosome
- engulfed from outside, break down of pathogen
- small chunks of antigen loaded on MHC II and travels to surface
- Talks to CD4+ T helper cell (provides help to get B cells to make antibodies)
where do the MHC processing pathways happen?
APCs begin processing antigen right after they have engulfed a pathogen; they will then travel through lymphatic vessels to a lymph node (or through blood to spleen) where they will present the antigens to naive T cells and B cells
t-cell activation in the lymph node
T cells are very particular and each only has one specificity of T-cell receptor
- a TCR will only react to one antigen
generation of diversity
the generation of a diverse repertoire of antigen-binding receptors on B or T lymphocytes that occurs in the bone marrow or thymus, respectively; germline and somatic diversification theory
germline theory
separate gene for each distinct receptor
somatic diversification theory
recombination of a limited # of gene sequences leading to a large # of distinct receptors
T and B cell development
some will be autoreactive and target “self” molecules, so therefore need to undergo negative selection to eliminate such cells; T cells may further undergo positive selection
negative selection
central tolerance; causing apoptosis in cells that are self-reactive
positive selection of T cells
MHC restriction; maturing only cells that can respond to the presentation of antigen on MHC
where does T cell development occur?
thymus; precursors travel from bone marrow to thymus and once matured travel to secondary lymphoid tissues
where does B cell development occur?
bone marrow; migrate to secondary lymphoid tissues once matured
clonal selection postulates
- each lymphocyte bears a single type of receptor w/ unique specificity
- interaction b/w a foreign molecule and lymphocyte receptor capable of binding that molecule w/ high affinity leads to lymphocyte activation
- the differentiated effector cells derived from an activated lymphocyte will bear receptors of identical specificity to those of the parental cell from which that lymphocyte was derived
- lymphocytes bearing receptors specific for ubiquitous self molecule are deleted at an early stage in lymphoid cell development and are therefore absent from the repertoire of mature lymphocytes
how does clonal selection occur?
APCs present antigen to T cell, only T cells with TCRs specific for the antigen will undergo clonal selection; antigen-specific T cells will proliferate and differentiate (in secondary tissues, results in swelling)
cellular immunity
immune response that relies on T cells to destroy infected body cells
humoral immunity
specific immunity produced by B cells that produce antibodies that circulate in body fluids
CD4+ T cells
helper T cells that carry the CD4+ protein antigen on their surface
CD8+ T cells
T cells whose role is cytotoxicity - “killer”
activation of B-cells (T cell dependent)
- B-cell must first encounter antigen, unprocessed antigen binds to BCR to activate B cell (weak), B cell presents processed antigen in the context of MHCII
- Interaction w/ helper T cell, binding of TCR to MHCII represents the first signal; release of interleukins by the T cell provide second signal for strong activation of B cell
costimulation
done by several interleukins; helper T cell recognizes the B cell is displaying processed antigen and releases costimulators for a second stronger activation of B cells
activation of B-cells (T cell independent)
if a pathogen expresses a large antigen w/ repeating subunits, it can bind several BCRs at once resulting in BCR cross-linking; this results in a signal being prod. in the B cell leading to B cell activation (this process results in weak B cell activation and develops poor immunologic memory)
what are the functions of antibodies?
complement activation, antibody-dependent cellular cytotoxicity, opsonization, neutralization immobilization
what are the 4 classes of antibodies?
IgG, IgA, IgE, IgM
IgG
most abundant throughout body, secondary responses, neutralize/opsonize/activate complement system, placental transfer
IgA
secreted dimer, mucosal surfaces (tube-like structures in body)
IgE
binds mast cells, responsible for allergies, protects against worms (in GI tract)
IgM
pentameter, primary responses, only present in circulation (too big), fixes complement
