How does the Immune System Recognise Pathogens? Flashcards
what is an immunogen?
what is an epitope?
immunogen: anything that elicits an immune response - most (but not all) antigens are immunogens
epitope: portion of antigen that is recognised and bound by a receptor on an immune cell
what is v basic overview of how antigen recognition occurs?
what is the capacity of innate immune cells, compared to adaptive immune cells, in no. of antigens recognised?
- *innate**: recognise a few common microbrial structures that are present in microbes but not humans = few antigens can be recognised.
- *adaptive (**lymphocytes - T/B cells): recognise millions of antigens. each individual T/B cell in body recognises different antigens - will be specific for single antigen
how do innate immune cells recognise antigens?
how do u describe innate immune cells’ response to self?
have Pattern Recognition Receptors (PRRs) recognise Pathogen Associated Molecular patterns (PAMPs) (structures found in microbes but not people - limited no. of structures)
- can be on surface, in lysosomes or cytoplasm
inherent lack of response to self (tolerance) - antigens arent present
what are Toll like receptors?
which TLR recognise flagella and LPS?
what happens as a response to TLR engagement?
- *Toll-like receptors: examples of PRRs:**
- TLR-5: recognises flagella
- TLR-4: recognises LPS (on gram-negavtive bacteria)
get both them on plasma membranes and in lysosomes.
- *TLR engagement:**
- dimerization of receptor
- activation of kinases
- activation of TF
- causes production of cytokines
wha
how do `T and B cells recognise antigens? - what does this mean with specificity?
- each new lymphocyte only expreses one type of receptor and recognises only one type of antigen: means specificity is rare
- *antigen introduced:**
- only activates lymphocytes with correct receptor
- lymphocytes clonal expansion -> expresssing same receptor
- causes lots of daughters cells
how do B cells recognise antigens?
- B-cells have recognition molecules called immunoglobins (Ig): often the eptiope is conformational
- B-cells recognise antigens directly (without help of other cells)
- activated B cells differentiate into plasma cells: secrete immunglogulin (‘antibody’)
what is the structure of an antibody?
- *constant region:** same between different antibody molecules
- *variable region:** differentates between the antibodies.
what are different classes of antibody?
what is specif
- B-cells –> plasma cells: can make different classes of antibody (isotopes):
- each antibody class can mediate different biological functions:
- *antibodies**:
- IgM
- IgG
- IgE
- IgA
the specificity of these are identical (still recognise the antigen that was bound to B-cell), but the constant parts vary:mediating different biological functions
- B cell always initially makes IgM - made in first in immune response but then swtiches to making IgG
- IgG decreases but then increasees massively when have secondary response
- antibody specificity remains constant - whilst biological effector functions are varied
how is the great number of receptor diversity generated on antibodies?
- each developing B cells expresses a distinct receptor
- not different genes for millions of different receptors
- INSTEAD: diversity is generated by mixing and matching gene segements within the heavy and light chain loci:
- Immunglobin heavy chain has:
a) V segments (40); b) D segments (25); c) J segments (6)
- get splicing of each of ^ to make lots of different genes: combinatorial diversity
- also: additional nucleotides can be added at the joints of ^^ to make more variation: junctional diversity
THEN:
any of immunoheavy chain stuff can associate with any of the light chains: more diversity: combinatorial diversity
how do t cells recognise antigens? what are the distinguishable features?
- use **TCR - T cell receptor
- T cells are presented antigens byantigen presenting cells (APCs):recogniselinear antigens
- **The APC presents the antigen to the T cell using the major histocompatability complex (MHC)
how does antigen recognition differ between T cells and B cells?
- T cells: use APCs, B cells do not
- T cells recognise short, linear peptide antigens, B cells recognise conformational epitopes
what is the structure of T cell receptor like?
- two chains: alpha and beta chains
- both chains have a constant (same between all TCR) and a variable region (different: recognises different antigens)
- antigen recognition with the peptide and MHC happens at the top
how do we get such a wide variety of TCR diversity?
somatic DNA recombination (like in B cells)
get multiple variable regions (see slide) and get variable splicing
what are the two types of MHC cells? which cells express each type?
- *MHC Class 1:** expresed by all cells. made from:
- alpha chain with 3 domains
- peptide-binding cleft between a1 and 2 (see slide)
- alpha chain is encoded by MHC.
- alpha chain associates with B2 microglobulin
- *MHC Class 2:** expressed by APC cells only
- alpha and beta chains (both formed by cell)
- peptide-binding cleft: formed from B1 and alpha1
Both have peptide-binding cleft: but the fit between the amino acid side chains inthe peptide and the grove of MHC molecule determine binding
