Immunology Exam 2
Antigen-binding site
The region of an antibody capable of interacting with antigens to initiate an immune response. Also known as complementarity determining region.
Pepsin
Proteolytic enzyme whose cleavage of immunoglobulin releases two F(ab')2 fragments and degrades the Fc region
IgM and mu heavy chains
An antibody class that serves as a receptor on naive B cells. Alse the first class of antibody to be secreted during the course of the immune response. When secreted, exists primarily in pentameric form.
Mature B cell
A B cell expressing both IgM and IgD
Heterokaryon or hybrid cell
A cell containing two or more genetically different nuclei; in immunology, hybridomas are used to produce monoclonal antibodies
Follicular dendritic cell
A cell with extensive dendritic extensions that is found in the follicles of lymph nodes. Although they do no express class II MHC molecules, they are richly endowed with receptors for complement and Fc receptors for antibody. they are of a lineage that is distinct from class II MHC-bearing dendritic cells.
Activated B cell
A mature B cell whose receptors have attached to an antigen and will respond to it
Frameshift mutation in Ig genes
A mutation that alters the reading frame of an Ig gene in some way; can be either productive or non-productive (the latter is more common). Examples include addition and deletion.
Open reading frame (ORF)
A part of a reading frame containing no stop codons
J-chain
A polypeptide that links the heavy chains of monomeric units of polymeric IgM and di-or trimeric IgA. The linkage is by disulfide bonds between the J chain and the carboxyl-terminal cysteines of IgM or IgA heavy chains.
Allelic exclusion
A process that permits expression of only one of the allelic forms of a gene
Papain
A proteolytic enzyme derived from papyas and pineapples. Papain cleavage of immunoglobulin releases two Fab and one Fc fragment per IgG
Framework regions of V region
A relatively conserved sequence of amino acids located on either side of the hypervariable regions in the variable domains of immunoglobulin heavy and light chains
Leader sequence on a nascent protein
A short hydrophobic sequence of amino acids at the N-terminus of newly synthesized immunoglobulins; it inserts into the lipid bilayer of the vesicles that transport Ig to the cell surface. The leader is removed from the ends of mature antibody molecules by proteolysis
Idiotypic determinants
A single antigenic determinant in the variable domains of an antibody or T-cell receptor; also call an idiotype. These are generated by the unique amino acid sequence specific for each antigen.
Ig superfamily
Know examples - any class of immunoglobulings, MHC cl I/II, CD4, CD8, FcR, poly IgR, TCR, CAMs Many are membrane bound
Cross-reactivity
Ability of a particular antibody to react with two or more antigens that possess a common epitope; used in research (Western blot, ELISA), but may cause false positives in clinical application
AID
Activation-induced cytidine deaminase; an enzyme that removes an amino group from deoxycytidine, forming deoxyuridine This is the first step in the process of both somatic hypermutation and class switch recombination.
Indirect ELISA
Adding antibody to well lined with antigen to measure level of antibody
DSBR enzymes used during DNA rearrangement
Aids in reforming double stranded DNA after rearrangement
Primary structure of a protein
Amino acid sequence
FcεR
An FcR specific for the Fc region of epsilon Ig molecules; present on cells responsible for releasing histamine and inducing an allergic response
Cysteine
An amino acid capable of binding to other molecules of the same type and forming strong disulfide bonds
Isotype
An antibody class that is determined by the constant-region sequence of the heavy chain. Five human isotypes are IgA, IgD, IgG, IgE, and IgM
Link between cross-reactivity and autoimmunity
An antibody that is able to recognize epitopes common to multiple proteins is more likely to recognize an epitope on a self protein that one that is specific to only one kind of protein
Allotypic determinants
An antigenic determinant that varies among members of a species or between different inbred strains of animals. The constant regions of antibodies possess allotypic determinants
Isotypic determinants
An antigenic determinant within the immunoglobulin constant regions that is characteristic of a species
Flow cytometry
Analysis of immune cells and their molecular markers based on presence/absence of those markers, which have been tagged with antibody
Anti-allotypic antibodies
Antibodies directed towards allotypic determinants
Anti-idiotypic antibodies
Antibodies directed towards antigenic determinants located in the antigen binding site of other antibodies
Anti-isotypic antibodies
Antibodies directed towards antigenic determinants located in the constant regions of antibodies that are shared among all members of a species
IgE and epsilon heavy chains
Antibodies responsible for the allergic response (formerly parasites, but because they are rare now, function against allergens)
Antigen (Ag)
Any substance (usually foreign) that binds specifically to an antibody or a T-cell receptor; often used as a synonym for immunogen
S-exon on Ig HC gene
Located to splice out different C isotype regions to alter expression of C segment
B cells versus activated B cells versus plasma cells
B cells - express immunoglobulin to detect immunogens Activated B cells - B cells that have been stimulated by an antigen Plasma cells - high affinity B cells that secrete different isotypes of antibodies during infection
Promoters and enhancers in Ig genes
Brought closer together by splicing and recombination to ensure expression only when rearrangement is completed
Antigenic specificity
Capacity or antibody and T-cell receptor to recognize and interact with a single, unique antigenic determinant or epitope
FcR
Cell-surface receptor specific for the Fc portion of certain classes of immunoglobulin. It is present on lymphocytes, mast cells, macrophages, and other accessory cells.
Ig-fold
Characteristic structure in immunoglobulins that consists of a domain of 100 to 110 amino acids folded into two beta-pleated sheet, each containing three or four antiparallel beta strands and stabilized by an intrachain disulfide bond
Ab affinity
Combined strength of all non-covalent interactions between a single antigen binding site on an antibody and a single B-cell epitope on the antigen
CTL
Cytotoxic T lymphocytes; an effector T cell that can mediate the lysis of target cells bearing antigenic peptides complesed with a class I MHC molecule
Humanized monoclonal antibodies for clinical applications
Increases the half life of Ab because the humanized portion of the heavy chain is less likely to be degraded; the entire process of hybridoma formation cannot be done with humans because we require our spleens to be intact
Booster shot (immunization)
Inoculation given to stimulate and strengthen an immunological memory response
Pro-B cell
Earliest distinct cell of the B-cell lineage
Conformational determinants
Epitopes of a protein that are composed of amino acids that are close together in the three-dimensional structure of the protein but may not be near each other in the amino acid sequence
Immature B cell
Express a fully-formed IgM receptor on their cell surface. Contact with antigen at this stage of B cell development results in tolerance induction rather than activation. Express lower levels of IgD and higher levels of IgM than mature B cells. Also have lower levels of anti-apoptotic molecules and higher levels of Fas than mature B cells, reflective of their short-half lives.
IgD and delta heavy chains
Expressed in mature, naive B cells
FACS-analysis and flow cytometry
Fluorescence activated cell sorter; used to analyze and sort individual ceells from complex cell suspension. Each cell is analyzed based on presence/absence of molecular markers, which have been tagged with antibody
Germ-line DNA versus rearranged DNA at Ig-loci
Germ line DNA contains all of the possibilities of Ig proteins; rearranged DNA has been spliced to only produce one specific molecule
Coding segments (V, D, J)
Heavy chain - V, D, J Light chain - V, J DNA segments that are recombined to make contact with each other and be expressed together; this recombination serves to increase diversity within B cells and antibodies
Role of disulfide bonds in formation of Ig molecule
Helps to stabilize and strengthen bonds
Recombination signal sequences (RSS)
Highly conserved heptamer and nonamer nucleotide sequences that serve as signals for the gene rearrangement process and flank each germ line V, D, and J segment
Cell-mediated immunity
Host defenses that are medicated by antigen-specific T cells. It protects against intracellular bacteria, viruses, and cancer and is responsible for graft rejection. Transfer of primed T cells confers this type of immunity of the recipient.
in-frame and out-of-frame joining of segments
In-frame - maintains proper reading frame Out-of-frame - introduces early stop codon to prevent complete function of protein
Ig classes and subclasses (isotypes)
IgM IgG - IgG1, IgG2, IgG3, IgG4 IgA - IgA1, IgA2 IgE IgD
One turn/two turn RSS
Immunoglobulin gene-recombination signal sequences are separated by an intervening sequence of 12 base pairs
Light chains
Immunoglobulin polypeptides of the lambda or kappa type that join with heavy chain polypeptides to form the antibody heterodimer
Antibody (Ab)
Immunoglobulin proteins consisting of two identical heavy chains and two identical light chains, that recognize a particular epitope on an antigen and facilitates clearance of that antigen. Membrane-bound Ab is expressed by B cells that have not encountered antigen; secreted Ab is produced by plasma cells. Some Abs are multiples of the basic four-chain structure.
Monoclonal versus polyclonal antibodies
Monoclonal - deriving from a single clone of dividing cells (only one type of antibody) Polyclonal - a mixture of antibodies produces by a variety of B-cell clones that have recognized the same antigen, although all of the antibodies react with the immunizing antigen, they differ from each other in amino acid sequence
IgG and gamma heavy chains
Most important antibody for immunization; 2nd most important for immune response/memory; 4 subclasses; can cross placenta
Productive versus non-productive rearrangements
Non-productive - introduce stop codon early in nucleotide sequence and prevent continued expression Productive - introduce diversity into genome without introducing new stop codon
Immunoglobulin protein fragments formed by pepsin versus papain
Pepsin - F(ab')2 (cuts below disulfide bond on heavy chain Papain - Fab (cuts Ag above disulfide bond)
Example 2 of alternative RNA splicing in Ig genes
Polyadenylation RNA splicing
Primary versus secondary antibodies and use in Western blot and ELISA
Primary antibodies - specific to the antigen of interest Secondary antibodies - directed against isotypic determinants on primary antibody Use of secondary antibodies - amplification
Cell differentiation
Process by which unspecialized or less specialized cells become more specialized
RAG-1 and RAG-2
Recombinases; only expressed when needed for rearrangement; only in B and T lymphocytes
Effect of chemical reduction on the structure of Ig molecule (eg. beta-mercaptoethanol)
Reduction of disulfide bonds can disconnect heavy and light chains of Ig and creates single strands of amino acids
Immunodominant epitope
Referring to antigenic determinants that produce a more pronounced immune response than others under the same condition
Fab fragment
Region at the N-terminus of the antibody molecule that interact with antigen. This antibody fragment, consisting of one light chain and part of one heavy chain, linked by an interchain disulfide bond, is obtained by brief papain digestion
Fc fragment
Regions at the C terminus of the antibody molecule that interacts with Fc receptors on other cells and with components of the complement system. This crystallizable antibody fragment consists of the carboxyl-terminal portions of both heavy chains and is obtained by brief papain digestion.
M1 and M2 exons on Ig-gene
Required for membrane binding of Ig molecules
ELISA
Sandwich - Measures the level of an antigen/protein using Ab coated well Indirect - Measures level of an antibody using Ag coated well
Example 1 of alternative RNA splicing in Ig genes
Secreted versus nonsecreted (membrane) Ig
IgA and alpha heavy chains
Seen in areas in close contact with the outside world; exists as monomer, dimer, or tetramer; j-chain holds multiple IgA molecules together; contains secretory component which allows transportation of IgA from site of formation to lumen where it will function
Germ-line model
States that all Ig molecule segments are encoded by all different genes; this would take up 15% of the genome, which is highly unlikely
Immunofluorescence
Technique of staining cells or tissues with fluorescent antibody and visualizing them under a fluorescent microscope.
C regions: CH and CL
The 3' coding of a rearranged immunoglobulin gene. There are multiple C gene segments in germ-line DNA, but as a result of gene rearrangement and, in some cases, RNA processing, only one segment is expressed in a given protein. CH- on the heavy chain; CL - on the light chain
Agglutination
The aggregation or clumping of cells or particles; in particular, a hemagglutinin (HA) causes clumping of red blood cells
DNA-rearrangement or recombination
The alteration of germ line DNA to permanently alter its structure and ensure the expression of a single protein type; ex. the rearrangement of the VDJ region of a heavy chain
Plasma cell
The antibody-secreting effector cell of the B lineage
Class switching
The generation of antibody genes for heavy chain isotypes other than mu or delta by DNA recombination
Affinity maturation
The increase in average antibody affinity for an antigen that occurs during the course of an immune response or in subsequent exposures to the same antigen
Heavy chains
The larger polypeptide of an antibody molecule; it is composed of one variable domain VH and three or four constant domains (CH1, CH2, etc.). there are five major classes of heavy chains in humans, which determine the isotype of an antibody.
Constant region domains
The nearly invariant portion of the immunoglobulin molecule that does not contain antigen-binding domains. The sequence of amino acids in the constant region determines that isotype of heavy chains and the type of light chains
Coding joint
The nucleotide sequences at the point of union of coding sequences during V(D)J rearrangement to form rearranged antibody or T-cell receptor genes
B cell epitopes
The portion of an antigen that is bound by an antibody; also known as an antigenic determinant
Epitopes or antigenic determinants
The portion of an antigen that is recognized and bound by an antibody or TCR-MHC combination
Complementarity determining region (CDR) or hypervariable region (HVR)
The same thing! Those parts of the variable regions of the BCR and TCR that exhibit the most sequence variability and interact with the antigen.
Pre-B cell
The stage of B-cell development that follows the pro-B stage. Produce cytoplasmic mu heavy chains and most display the pre-B cell receptor
Alternative RNA splicing in Ig genes
The variable splicing of mRNA transcripts from DNA to create variation in Ig gene products
Gene-segment model
Theory stating that Ig genes are encoded by multiple gene segments and vary due to random rearrangement at the genomic level
HVR1, 2, and 3
Those parts of the variable regions of the BCR and TCR that exhibit the most sequence variability and interact with the antigen.
Ig domains - structure and function
Three dimensional structures characteristic of immunoglobulin and related proteins including T cell receptors, MHC proteins, and adhesion molecules. Consists of a domain of 100 - 110 amino acids folded into two beta-pleated sheets, each containing three or four antiparallel beta strands and stabilized by an intrachain disulfide bond.
F(ab')2 fragment
Two Fab units linked by disulfide bridges between fragments of the heavy chain. They are obtained by digestion of antibody with pepsin.
HAT selection
Unmerged myeloma cells that do not form hybridomas with lymphocytes cannot survive in HAT medium, which results in their death
One-turn-two-turn joining rule
Upon rearrangement, one-turn RSS's can only join with 2-turn RSS's
Hapten-carrier conjugate
Use in hybridomas; used to select for multiple different antibodies specific for different B cell epitopes
ELISPOT
Used to detect percent of secreting cells in a heterogeneous cell/tissue sample
Ig gene segments (V, D, J)
V - variable region of the gene D - diversity region; only in heavy chain J - joining segment
Hybridomas
What are they used for? Production of monoclonal antibodies How are they generated? Fusion of myeloma cells with lymphocytes (from mice/other animal)
