ICL 1.1: Introduction to Adaptive Immunity Flashcards
what is an antigen?
any molecule that stimulates the immune system
- proteins
- environmental like dust or pollen
what is an epitope?
the specific region of an antigen that binds the immunoreceptor
an antigen can have multiple epitopes
what is the cellular part of the adaptive immune system?
cell-mediated immunity by T cells
secreted and/or cell surface molecules
they provide signals for the maturation and/or
differentiation of other leukocytes
what is the humoral part of the adaptive immune system?
antibody mediated by B cells
antibodies target cells and molecules for removal
what are APCs?
antigen presenting cells
includes macrophage, dendritic, epithelial, and B cells
where are lymphocytes usually found?
lymphoid tissues and organs
what are primary/central lymphoid tissues?
sites of where lymphocytes develop and mature
T cells = thymus
B cells = BM
what are secondary lymphoid tissues?
they’re distributed throughout the body and are sites where naive lymphocytes encounter antigen and become activated
ex. lymph nodes, spleen, adenoids, tonsils, Peyer’s patches in SI, appendix
where do antigens go once they’re inside the body?
antigens are carried to the naïve lymphocytes in secondary lymphoid tissue, via the lymphatics
where are lymph nodes located?
lymph nodes lie at the junctions of lymphatic vessels, which collect extracellular fluid (lymph) from the tissues
antigens found in the tissues eventually are carried to lymph nodes
what are the functions of the spleen?
- a site of lymphocyte activation for blood-borne antigens
2. storage of immune memory (memory lymphocytes)
where are the B and T cells located in the spleen?
the white pulp!!!
B cells are in the germinal center
T cells are in the PALS
what is GALT?
gut associated lymphoid tissues
ex. tonsils, adenoids, appendix, Peyer’s patches
what is BALT?
bronchial associated lymphoid tissues
lymphoid tissue that lines the respiratory tract
what type of antibody does the GI tract have alot of?
IgA
what does TCR stand for?
T-cell receptor
how does antibody binding work?
Ig/TCR are highly specific for a given antigen
antibodies made during infection with measles virus bind to the virus and prevent reinfection with measles virus
but antibodies made during infection with measles virus do not bind to influenza virus
what are TCRs?
T cell receptor recognizes peptide associated with MHC molecule
MHC = major histocompatibility complex
how is our immune response made specific?
the specificity of our immune responses resides in receptors like TCR and B cell receptors
what does a B cell receptor do?
it’s a surface immunoglobulin that recognizes an antigen
what’s the structure of a B cell receptor?
the immunoglobulin molecule is composed of two pairs of chains (H-heavy and L-light; mw), each of which can be divided into domains based on sequence similarity:
- V region (variable)
- C region (constant)
surface immunoglobulin has a light chain and a heavy chain
there’s also a transmembrane region and an antigen-binding site
what’s the difference between the structure of an antibody and B cell receptor?
surface immunoglobulin has a transmembrane region that an antibody doesn’t have
what’s the structure of a TCR?
TCR is made of an α and β chain
there’s an antigen binding site that is both on the α and β chain
there’s also a transmembrane region
what are the different regions of the light and heavy chains of immunoglobulin?
both the light and heavy chain can be divided into domains = V region and C region
the V-region is variable and where there’s antigen binding
the C-region is constant and is what engages the innate immune system
what defines an immunoglobulin’s antigen specificity?
hypervariable domains in each V region
you can look at the AA that make up both the heavy chain V region and the light chain V region
depending on which AAs are present in the binding pocket, it will tell you which antigen is most likely to bind
where do antigens bind to immunoglobulin?
antigens bind in the pockets of the hyper variable regions of each arm of the immunoreceptor
in the V-region
what are the steps in clonal selection?
during development, progenitor cells give rise to large numbers of lymphocytes, each with a different specificity
after an pathogen binds to a lymphocyte, there’s proliferation and differentiation of pathogen-activated lymphocytes to form a clone of the effector cell specific to that pathogen
effector cells eliminate pathogens!
clinical selection leads to the expansion of antigen-specific and pathogen-specific lymphocytes
what is clonal selection?
each lymphocyte bears a single type of receptor of a unique specificity
interaction between a foreign molecule and a lymphocyte receptor leads to lymphocyte activation
activated lymphocytes will bear receptors of identical specificity to those of parental cell
lymphocytes bearing receptors for self molecules are deleted at an early stage in lymphoid cell development
what do T cell antigen receptors recognize?
B cell produce Ab that can recognize native or denatured molecules
however, T cell antigen receptor CANNOT recognize intact protein antigens, but responds to peptide fragments bound to the surface of another cell (antigen presenting cell)
T cells respond to a peptide bound to a MHC molecule displayed on the surface of another cell, called an antigen presenting cell (APC)
what does MHC stand for?
major histocompatibility complex
what are class I MHC molecules?
class I MHC molecules are expressed on the surface of ALL nucleated cells
they’re recognized by TCR of cytotoxic T cells (CD8)
**CD8 binds to class I MHC-peptide complex
source of peptide is in the cytoplasm
what are class II MHC molecules?
class II MHC molecules are expressed on the surface of some nucleated cells, mainly APCs
they’re recognized by TCR of helper T cells (CD4)
**CD4 binds to class II MHC-peptide complex
source of peptide is in the phagosomes
what’s the function of MHC molecules?
they’re used to activate T cells
MHC I binds peptides from proteins found in the cytoplasm
MHC II binds peptides from proteins found in the phagosomes
how do class I MHC molecules work?
MHC I binds peptides from proteins found in the cytoplasm
- virus infects cell
- viral proteins synthesized in cytoplasm
- peptide fragments of viral proteins are bound by MHC class I in ER
- bound peptides are transported by MHC class I to the cell surface of CD8 cells
- cytotoxic T cells recognize the complex of viral peptide with MHC class i and kills the infected cell
how do class II MHC molecules work in a macrophage?
MHC II binds peptides from proteins found in the phagosomes
- macrophage engulfs and degrades bacterium, producing peptides
- bacterial peptides bound by MHC class II inside vesicles of macrophage
- bacterial peptides transported by MHC class II to the cell surface of macrophages
- TH1 cell recognizes the complex of peptide antigen with MHC class II and activates macrophage
how do class II MHC molecules work in a B cell?
MHC II binds peptides from proteins found in the phagosomes
- cell-surface immunoglobulin of B cell binds and engulfs and degrades bacterium, producing peptides
- bacterial peptides bound by MHC class II inside vesicles of macrophage
- bacterial peptides transported by MHC class II to the cell surface of macrophages
- TH2 cell recognizes the complex of peptide antigen with MHC class II and activates B cell
what’s the purpose of vaccines?
vaccination with pathogen-specific antigens or pathogens allows us to mimic the infection and induce protective immunity without inciting the primary disease
how do allergies work?
allergies are unwanted inflammatory response that are mediated by the adaptive immune response
inhalation of pollen particles produces the symptoms of a respiratory infection through IgE-mediated degranulation of mast cells
mast cells release cytokines, histamine and other active substances
what happens after a pathogen is recognized by the innate immune system?
after recognition of pathogen by innate system, APC’s present antigen to adaptive system to mount a clonal response
- microbes enter through and break in skin and are phagocytksed by dendritic cells
- dendritic cell matures and carries microbial antigens to local lymph node to become an antigen-presenting cell
- APCs activates T cells to respond to microbial antigens
- activated T cells migrate to site of infection to help eliminate residual microbes
