Chapter 5: Cells and tissues of the immune system Flashcards
What are major components of the innate immune system?
Epithelial barriers, phagocytic cells (neutrophils and macrophages), dendritic cells, natural killer cells. But also plasma proteins, like proteins of the complement system.
What’s the difference between naïve, effector and memory lymphocytes?
Naïve lymphocytes express an antigen receptor but have not responded to antigens and do not serve any function.
Effector lymphocytes are induced by lymphocyte activation and perform the functions that eliminate microbes.
Memory lymphocytes, induced during activation, survive in a functionally silent state even after the antigen is eliminated and respond rapidly upon subsequent encounters with the antigen.
What two reactions can be provided by the innate immune system when triggered?
Inflammation and anti-viral defense.
Antibodies provide protection against intracellular or extracellular pathogens?
Extracellular
T lymphocytes provide protection against intracellular or extracellular pathogens?
Intracellular
What are peripheral (secondary) lymphoid organs?
The lymph nodes, spleen and mucosal tissues.
What is clonal selection (in short)?
Foreign antigens are concentrated in
these organs, where they bind to and activate the clones of lymphocytes that express receptors for those antigens.
What do T cells recognise: whole antigens or peptide fragments?
They recognize peptide fragments of proteins displayed by MHC-molecules. Therefore they only recognise antigens presented by other cells.
Describe the T-cell receptor (TCR).
It’s a heterodimer that is composed of (disulfide-linked) α and β protein chains. Each chain has a variable region that participates in binding a particular peptide antigen
and a constant region that interacts with associated signalling molecules
By which polypeptide chains is a TCR surrounded (or noncovalently linked)? What are its functions?
The TCR is surrounded by two CD3 proteins (composed of γ, δ, and ε proteins) and next to the TCR 2 ζ chains reside. They do not bind antigens, but initiate intracellular biochemical signals after TCR recognition of antigen.
CD28 is a receptor on T cells that can bind costimulators that are induced by APCs and binds adhesion molecules that strengthen the bond between the T cell and APC and control the migration of the T cells to different tissues.
What other molecules are expressed by T cells and what do they bind to?
T cells can also express CD4 or CD8, they act as co-receptors during T-cell activation. CD4 binds to invariant portions of class II MHC molecules. CD8 binds to class I MHC molecules.
What’s the difference between CD4+ and CD8+ T cells?
CD4+ T cells are called helper T cells, they secrete cytokines that help B cells to produce antibodies and also help macrophages to destroy phagocytosed microbes. CD8+ T cells are called cytotoxic T lymphocytes and also secrete cytokines, but their most important role is to directly kill
virus-infected cells and tumor cells.
What are regulatory T lymphocytes?
T cells that function to suppress immune responses.
Just read
While most T cells express TCRs composed of α and β
chains, a minority of peripheral blood T cells and many T
cells associated with mucosal surfaces (e.g., lung, gastrointestinal tract) express TCRs that are composed of γ and
δ chains, which are similar but not identical to α and β
chains. Such γδ T cells, which do not express CD4 or CD8,
recognize nonprotein molecules (e.g., bacterial lipoglycans), but their functional roles are not well understood.
Just read
Another small population of T cells expresses markers
of both T cells and NK cells. These so-called NKT cells
recognize microbial glycolipids and may play a role in
defense against some infections. The antigen receptors of
γδ T cells and NKT cells recognize antigens independently
of MHC molecules, and are much less diverse than the
receptors of the more abundant CD4+ and CD8+ T cells.
What is the function of MHC molecules?
To display peptides for recognition by CD4+ and CD8+ T lymphocytes.
What is MHC restriction?
A phenomenon where T cells only recognise peptides displayed by that person’s MHC molecules (the onlly MHC molecules that the T cells normally encounter).
Fill in (…. or /):
Class I MHC molecules are expressed on specific/all (1)(nucleated) cells, are encoded by thee closely linked loci, designated HLA-..(2), HLA-… (3) and HLA-… (4).
Each of these molecules consists of a polymorphic α chain noncovalently associated with an invariant β2-
microglobulin polypeptide (encoded by a separate gene
on chromosome 15). The extracellular portion of the α chain contains a … (5) where the polymorphic residues are located and where … (6) peptides bind to MHC molecules for presentation to T cells, and a conserved
region that binds CD…(7), ensuring that only CD…(8) T cells
can respond to peptides displayed by class I molecules.
(1) : all nucleated cells
(2) : A
(3) : B
(4) : C
(5) : cleft
(6) : foreign
(7) : 8
(8) : 8+
Fill in (…. or /):
Class II MHC molecules are encoded by genes in the HLA-…(1) region, which contains three subregions: …(2),
…(3), and …(4). Class II molecules are heterodimers of
noncovalently linked α and β subunits (see Fig. 5.6).
Expression of class II MHC molecules
is restricted to a few cell types, mainly APCs (notably,
….(5)), …(6), and …(7). The extracellular portion of class II MHC molecules contains a cleft
for the binding of antigenic peptides and a region that
binds …(8).
(1) : D
(2) : DP
(3) : DQ
(4) : DR
(5) : dendritic cells
(6) : macrophages
(7) : B cells
(8) : CD4
What is an HLA haplotype and how does this occur?
The HLA genes are closely linked on chromosome 6, so when passed from parent to offspring these genes will pass as a whole and behave like a single locus with respect to their inheritance patterns. Eacht set of maternal and paternal HLA genes is then referred to as an HLA haplotype.
What is the probability that two siblings will share the same two HLA haplotypes?
25%
What’s the relation between HLA genes and immune respons to a donor organ?
Because each person has HLA alleles that differ to some extent from those of every other unrelated individual, grafts from unrelated donors will elicit immune responses in the recipient and be rejected.
Why can an immune response still be elicited during transplantation even though the donor is the sibling from the recipient and has the same HLA halpotype?
Because of minor histocompatibility loci
Just read (because hopefully already obvious)
Whereas T
cells recognize only MHC-associated peptides, B cells recognize and respond to many more chemical structures,
including soluble or cell-associated proteins, lipids, polysaccharides, nucleic acids, and small chemicals, without a
requirement for the MHC.
