Adaptive Immunity 1 Flashcards
What cells are involved in humoral immunity?
B cells
What cells are involved in cell-mediated immunity?
T cells
B cell antigen
A substance that binds an antibody (protein, carb, or DNA)
Epitope
Portion of antigen recodnized by an antibody
Polyclonal antisera
A collection of different antibodies from serum that recodnize different epitopes of the same Ag
monoclonal antibody (mAb)
Antibody derived from a single B cell clone (B cells only have 1 specificity for 1 epitope and they propagate via colonal selection)
Describe the structure of an antibody.
- comrised of 2 identical heavy and light chains that are held together by inter-chain disulphide bonds
- has variable and constant reigons
- has 2 Fab domains and 1 Fc domain
How many genes/alleles encode for the antibody and what are they called (if noted)
- 2 light chain genes (kappa and lambda; 4 alleles)
- 1 heavy chain gene (2 alleles, but 5 isotypes: IgM, IgG, IgE, IgA, and IgD)
Variable reigon
Area on the Ab that contains different antibody specificity and binds the antigen (heavy chain: VH; light chain:VL)
Constant regions
Area of the Ab that are important for the structure of the Ab and some parts (the C-terminal constant reigons) have effector function
What does each VH/VL and CH/CL form?
A conserved structure
What immune proetins have immunoglobulin domains?
TCR alpha and beta chains, CD4, CD8, MHC class 1 and 2
Describe the immunoglobulin domain.
- about 110 aa in size
- each domain consists of 2 beta sheets that form a beta sandwitch/barrel structure which is held togther b a disulfide bond and hydrophobic interactions between the sheets
- have complementary determining reigons
Complementary determining reigons (CDRs)
area in the heavy and light chain that form the antigen binding site and are highly varibale between antibodies of different specificities (there are CDRs in the TCR that also form the antigen binding site)
B cell receptor (BCR)
aka, mIg (membrane immunoglobulin) and sIg (surface immunoglobulin)
a modular receptor involved in antigen binding and signalling
What are the signaling subunits in the BCR?
Igalpha and Igbeta
What is BCR signalling critical for?
- B cell development
- mature and memory B cell activation
- survival of mature naive B cells (B cell that has not encountered an antigen)
ITAM
ask!!!
TCR (T cell receptor)
modular receptor of the T cell that has antigen binding subunits and signalling subunits
Antigen binding subunits of the TCR and their function
- alpha chain (similar to Ab light chain) and beta chain (similar to the Ab heavy chain)
- they bind specific MHC + peptide combinations (T cell antigen)
What MHC do CD4 cells bind? CD8?
CD4+: MHC II + peptide
CD8+: MHC I + peptide
Signalling subunits of the TCR and their function
- collectively called CD3
- Subunits possess ITAM motifs
What is TCR signalling critical for?
- T cell development
- Activation of mature/memory T cells
- T effector cell function
- Survival of mature and naive T cells
What are the functions of Antibodies?
- Neutralization of pathogens and toxins (prevents cell binding)
- Agglutination of partivulate antigens (prevents cell binding and enhances clearance)
- Opsinization (increases phagocytosis)
- Complement activation leading to pathogen lysis
- ADCC (Antibody-dependent cell mediated cytoxocity) which leads to NK cell induced apoptosis
- Degranulation of granulocytes (antibodies trigger this)
What determines the Ab function of a specific Ab?
Their isotype constant (Fc) reigons
Ab Isotype
- heavy chain contant reigons (this varies amoung different Ab)
How do Ab isotypes differ?
with respect to sequence and number of heavy chain Ig Domains (4-5 domains/heavy chain)
What are the 5 main isotypes in humans?
IgM, IgD, IgG, IgA, and IgE
Where do you find Ab’s?
They can be secreted by B cells or they are expressed on the surface of B cells
Which Ab(s) activate the classical complement pathways?
IgG1, IgG2, IgG3 and IgM
IgG3 and IgM do this the best
Which Ab(s) can cross the placenta?
IgG1, IgG2, IgG3, and IgG4
IgG1 and IgG4 do this the best
Which Ab(s) is/are present on the membrane of mature naive B cells?
IgM and IgD
Which Ab(s) bind to the Fc receptors of phagocytes?
IgG1, IgG2, IgG3, IgG4, IgA1, IgA2, and IgM
IgG1 and IgG3 do this the best
Which Ab(s) are involved with mucosal transport via the poly-Ig receptor?
IgA1, IgA2, and IgM
IgA1 and IgA2 do this the best
Which Ab(s) induce mast cell and/or basophil degranulation?
IgE and IgD
Match the Ab isotype with their heavy chain component.
(IgG1-4, IgA1-2, IgM, IgE, and IgD)
IgG1- gamma 1
IgG2- gamma 2
IgG3-gamma 3
IgG4- gamma 4
IgA1- alpha 1
IgA2- alpha 2
IgM- mu
IgE- epsilon
IgD- delta
Colonal Selection Theory
theoretical model to explain how pathogens select specific B cells to secrete Ab and how T cells are selected by Ag
What are the 4 postulates for the Colonal Selection Theory?
- Each B cell expresses on its surface an Ab with one specificity
- Ag selects specific B cell for activation
- Effector B cells (plasma cells and memory cells) have the same Ag specificity as the original B cell that was selected by Ag
- B cells that recodnize self Ag are removed from the repertoire during development
