Adaptive immune response Flashcards
B Lymphocytes
Are the source of circulating antibodies
T Lymphocytes
recognize peptides from pathogens presented by MCH molecules on infected cells or antigen-presenting cells
Antibody structure
composed of two identical heavy chain and two identical light chain polypeptides, where the variable region combine and form an antigen-binding site that dertermines antigen specificity.
Draining lymph notes
Periphereal lymphoid organs in which the free antigen and antigen-bearing dendritic cells activate antigen-specific lymphocytes, which leads to proliferation and differentiation whereafter most antibodies leave as effectors
M cells
specialized epthelial cells, collect antigens from the epithelial surfaces of the gastrointestinal tract
Paratope
region of antibody that recognizes and binds to the epitope of an antigen. Paratope are produced by the complementary binding of light and heavy chains that create a three-dimensional structure.
Idiotope
The antigenic determinants (epitopes) that are unique to a particular immunoglobulin, one that is directed against a particular antigen and is produced by a clone of cells, or unique to a T-cell receptor
Haptens
small antigens that can only stimulate production of anti-hapten antibodies when linked to a protein
Avidity
describes the measure of overall or accumulated strength of a protein-protein complex, i.e. The total strength of all the non-covalent interactions between an antibody binding to its ligand/s
MHC class I antigen
Resides on the surface of cells and recognizes peptides, 8-10 amino acids long. It is recognized by CD8 cytotoxic T-cells
MHC class II antigen
Resides in endosomes inside the cell and recognizes peptides 13 amino acids or longer. It then travels to the cell surface and is recognized by CD4 T-cells, which activates other cells
Antigenicity
the capacity of viruses to bind to specific antibody molecules
TCR co-receptors
CD4 and CD8 are important in the activation of T cells, primarily because of their ability to interact with the proteins of the MHC, enhancing recognition of the MHC–peptide complex by the T cell receptor (TCR)
CDRs
Hypervariable regions that interact with antigen (V-type)
RSS (recombination signal sequences)
Noncoding DNA sequences, that are found adjacant to the point at which recombination takes place of the antigen receptor loci and designate them for use by the RAGs
RAG-1 and RAG2
Proteins encoded by the recombination-activating genes RAG-1 and RAG-2, which form a dimer that initiates V(D)J recombination
Somatic hypermutation
Mutations in V-region DNA of rearranged immunoglobin genes that produce variant immunoglobins, for higher affinity binding to antigen. Affacts somatic cells exclusively
Class Switch
Somatic gene recombination in activated B-cells that replace one heavy-chain constant region with a different isotype, switching the isotype from IgM to the production of IgA, IgG and IgE (changes antibody effector)
V-region assembly
the variable region is a complete light-chain exon constructed from a variable (V) and a joining (J) gene segment in the genomic DNA.
Junctional diversity
Variability in sequence present in antigen-specific receptors that is created during the process of joining V, D and J gene segments, due to imprecise joining and insertion of nontemplated nucleotides at the joins between segments
Transcriptional activation
required to turn on the expression of genes in a eukaryotic cell. Activators bound to the enhancer can facilitate either the recruitment of RNA polymerase II to the promoter or its elongation
12/23 rule
Gene segment flanked by an RSS with a 12-bp spacer typically can be joined only to one flanked by a 23-bp spacer RSS
Class switch recombination
nonhomologous DNA recombination that is guided by stretches of repetitive DNA known as switch regions (lie in the intron between Jh gene segments and Cmhy gene. changes isotype.
Membrane vs secreted form (IgG’s)
membrane-bound form of Igs function as a BCR controlling maturation, activation, and differentiation of B cells, whereas the soluble secreted Igs, also known as Abs, contribute to the body’s immune surveillance mechanism through pathogen recognition and organization of immune reactions
IgM, IgD expression on surface
All naive B cells
VDJ recombination
Recombination og different gene segments into sequences encoding complete protein chains of immunoglobins and T-cell receptors
Self-antigen
Potential antigen on the tissue of an individual against which an immune response is not usually made except in the case of autoimmunity
AID (activation-induced cytidine deaminase)
Enzyme that initiates somatic hypermutation and isotype switching by deaminating DNA directly at cytosine in immunoglobin V regions or switch regions.
Ku70/Ku80
DNA repair protein required for immunoglobin and T-cell receptor gene rearrangement (double-strand break repair)
four main processes that generate the diversity in the lymphocyte repertoire.
1) Different combinations of V, D and J
2) Different combination of assembly of heavy and light chain, beta and alpha
3) P and N nucleotides, the P nucleotide arise from the cut of the artemis in the proximity of the hairpin structure (palindrome).
4) Somatic hypermutation (B-cell only)
Gene conversion
specific type of homologous recombination that involves the unidirectional transfer in the expressed rearranged V-region gene are replaced with sequences from an upstream V gene segment pseudogene
secondary diversification
- Somatic hypermutation and gene conversion, higher affinity and specificity
- Class switching recombination changes the effector function
Cyclic reentry model
explanation of B-cell behavior in lymphoid follicles, where B-cells in germinal centers lose and gain expression of chemokine receptor CXCR4 and move from light and dark zones
MAIT cells
gammadelta T-cells with limited diversity present in mucosal immune system, that responds to bacterially derived folate derivates presented by nonclassical MHC class Ib molecule MR1
Cross-presentation
Process by which proteins taken up by dendritic cells gives rise to peptides presented by MHC class I molecules. Enables antigens from extracellular sources to activate CD8 T cells
antigen processing
Intracellular degradation of foreign proteins into peptides that can bind MHC molecules for presentation to T-cells