L01 Flashcards
what is a pathogen
an organism that causes disease e.g.
bacteria
viruses
fungi
parasites
worms
protozoa
what are the features of specific immunity
is induced by exposure to a particular infection
shows a high degree of specificity
exhibits “memory”
mediated by lymphocytes (B/T cells)
clonally distributed receptors
large repertoire: low frequency of cells specific for any antigen
response takes time to develop
memory cells produced
(work better and faster next time)
what is clonal selection theory
removal of potentially self reactive immature lymphocytes (Self antigen receptor cells are destroyed to avoid auto immune reactions)
creating a pool of mature naive lymphocytes that react to foreign antigens
which receptor is always membrane bound
TCR
what is BCR called when released after B cell activation
antibody
what does TCR do
recognizes peptide fragment
of antigen bound to MHC
expressed by APC
what do TCR only recognize
peptides
what is the variable region of an antibody
form 2 identical antigen binding sites from heavy and light chains
what is the constant regions of an antibody
regions responsible for the structure of the antibody and interacting with other molecules (FcR, Compliment system) and cells of innate system
—-> antibody effector functions
what type of bonds hold the light and heavy chains
covalent and non-covalent
what are the types of light chains
λ & κ
how many types of light chains is present in 1 antibody
1
Each chain in an antibody has a variable and a constant region
true
what does the antigen binding site consist of
VH and VL
what are the classes of antibodies (isotypes)
IgM, D, A, G and E
what determines the isotypes of antibodies
heavy chain (C region)
how many domains does the L chain have
2
how many domains does the H chain have
4 or 5
how long is each domain
110 amino acids
what does each domain comprise
two b sheets
what are the antibody domains linked by
disulphide bridge (S-S, C)
domains are paired –> folded units within the protein
True
how many hypervariable regions (CDRs) are there in in the VH and VL
3 in each
how many antigen binding sites does 1 antibody have
2
how many hypervariable loops are there in each Ag binding site
6
how many hypervariable loops are there in an antibody
12
what are the types of antibody/antigen interactions
linear (continuous) epitope
non-linear (structural/3D/
discontinuous) epitope
what type of molecules can antigens be
All protein, polysaccharide even nucleic acids), along with non-biological molecules e.g. chemicals, metals
what type of interactions do Ag and antibodies form
non-covalent interactions
CDRs present in antibody V regions determine the specificity and the affinity of an antibody for Ag
true
which parts of the antibody interact with the epitope
hypervariable regions (CDRs)
what is the epitope
the part of the antigen that is recognized by the antibody
TCR binds free antigen
false
antigen is presented to TCR in the cleft/binding “groove” of MHC class I or class II molecules
true
how many Ig-like domains does TCR have
4
TCR recognizes short peptide fragments (of Ags) bound to MHC molecules on other cells
True
TCRs are heterodimers. what chains do they have
α and β chain (sometimes γ and δ)
what are the regions of each chain of TCR
a V and a C region
which domain of TCR interact with the antigen (peptide bound to MHC molecule)
V domain
how many CDRs does each chain of TCR contribute to Ag binding
3
what chromosome contains the MHC gene (HLA in humans)
6
how many classes of MHC molecules are there
2
where is MHC class 1 expressed
all nucleated cells
MHC class 1 molecule is a heterodimer: a chain (43 kD). b2- microglobulin (12 kD)
True
what are the different MHC class 1 molecules in humans
HLA-A, HLA-B and HLA-C
HLA-A, B and C molecules are encoded by separate a chain genes. A single (non-MHC located) gene encodes b2-microglobulin which associates with HLA-A, HLA-B and HLA-C
True
a1 and a2 domains fold to form b-sheet structure known as peptide binding site (“groove, cleft”) in MHC 1 molecule
True
which domains of MHC 1 are very polymorphic
alpha 1 and alpha 2
a3 domain/b2-microglobulin fold into “Ig-like” domains in MHC 1
True
MHC 1 has 2 transmembrane domains
false
what are the features of MHC class 2 molecules
expression limited to APC (and cytokine-activated cells)
heterodimers, a and b chains
similar size (34 and 29 kD) and both transmembrane
In humans three different MHC class II molecules: HLA-DP,
HLA-DQ and HLA-DR
a and b chains encoded by separate genes encoded within MHC
both a2 and b2 domains
are Ig-like
what are the different MHC 2 molecules in humans
HLA-DP,
HLA-DQ
and HLA-DR
how many transmembrane domains does MHC 2 have
2
MHC 2 groove is more open than “groove” seen in MHC class I molecules, and binds longer peptides
True
what molecule does CD8 bind
MHC class 1
what domain does CD8 bind
MHC class I a1/a2domains stabilizing
TCR/MHC interaction
what molecule does CD4 bind
MHC class 2
what domains does CD4 bind
binds MHC class II a2/b2 domains stabilizing
TCR/MHC interaction
