Chapter 5: Cells and tissues of the immune system Flashcards Preview

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Flashcards in Chapter 5: Cells and tissues of the immune system Deck (61)
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1
Q

What are major components of the innate immune system?

A

Epithelial barriers, phagocytic cells (neutrophils and macrophages), dendritic cells, natural killer cells. But also plasma proteins, like proteins of the complement system.

2
Q

What’s the difference between naïve, effector and memory lymphocytes?

A

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.

3
Q

What two reactions can be provided by the innate immune system when triggered?

A

Inflammation and anti-viral defense.

4
Q

Antibodies provide protection against intracellular or extracellular pathogens?

A

Extracellular

5
Q

T lymphocytes provide protection against intracellular or extracellular pathogens?

A

Intracellular

6
Q

What are peripheral (secondary) lymphoid organs?

A

The lymph nodes, spleen and mucosal tissues.

7
Q

What is clonal selection (in short)?

A

Foreign antigens are concentrated in

these organs, where they bind to and activate the clones of lymphocytes that express receptors for those antigens.

8
Q

What do T cells recognise: whole antigens or peptide fragments?

A

They recognize peptide fragments of proteins displayed by MHC-molecules. Therefore they only recognise antigens presented by other cells.

9
Q

Describe the T-cell receptor (TCR).

A

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

10
Q

By which polypeptide chains is a TCR surrounded (or noncovalently linked)? What are its functions?

A

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.

11
Q

What other molecules are expressed by T cells and what do they bind to?

A

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.

12
Q

What’s the difference between CD4+ and CD8+ T cells?

A

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.

13
Q

What are regulatory T lymphocytes?

A

T cells that function to suppress immune responses.

14
Q

Just read

A

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.

15
Q

Just read

A

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.

16
Q

What is the function of MHC molecules?

A

To display peptides for recognition by CD4+ and CD8+ T lymphocytes.

17
Q

What is MHC restriction?

A

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).

18
Q

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.

A

(1) : all nucleated cells
(2) : A
(3) : B
(4) : C
(5) : cleft
(6) : foreign
(7) : 8
(8) : 8+

19
Q

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).

A

(1) : D
(2) : DP
(3) : DQ
(4) : DR
(5) : dendritic cells
(6) : macrophages
(7) : B cells
(8) : CD4

20
Q

What is an HLA haplotype and how does this occur?

A

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.

21
Q

What is the probability that two siblings will share the same two HLA haplotypes?

A

25%

22
Q

What’s the relation between HLA genes and immune respons to a donor organ?

A

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.

23
Q

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?

A

Because of minor histocompatibility loci

24
Q

Just read (because hopefully already obvious)

A

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.

25
Q

There are two molecules on the surface of B cells. Which are these?

A

An immunoglobulin (IgM) together with a signaling molecule (like CD21 which recognizes complement breakdwon product).

26
Q

What happens after stimulation of B cells?

A

They differentiate into plasma cells, which secrete large amounts of antibodies.

27
Q

What isotypes/classes of immunoglobulins are there?

A

IgG, IgM, IgA (constitute more than 95% of circulating antibodies), IgE and IgD.

28
Q

Where do IgA, IgE and IgD reside?

A

IgA in mucosal secretions, IgE present in circulation at low concentrations and is found attached to mast cells and IgD is expressed on the surfaces of B cells but is secreted at very low levels.

29
Q

True or false:
NK cells are lymphocytes that arise from the same common
lymphoid progenitor that gives rise to T lymphocytes and
B lymphocytes.

A

True

30
Q

Are NK cells part of the innate or specific immune system?

A

Innate, as they are functional without prior activation and
do not express highly variable and clonally distributed
receptors for antigens.

31
Q

What kind of receptors do NK cells express and when are these receptors expressed?

A

They express inhibitory and activating receptors.
Inhibitory receptors are expressed on all healthy cells and recognise self class I MHC molecules.
Activating receptors recognise molecules that are expressed when a cell is stressed or infected.

32
Q

Is there a balance between inhibitory and activating receptors of NK-cells? (When) does this change?

A

Normally, the effects of inhibitory receptors dominate over those of activating receptors, preventing spontaneous activation of NK cells. During infection/stress there’s reduced expression of class I MHC molecules and increased expression of proteins that engage activating receptors. Here NK cells ae activated and the infected/stressed cells are killed and eliminated.

33
Q

What do NK cells secrete and what is the function?

A

Cytokines such as interferon-γ (IFN-γ), which
activates macrophages to destroy ingested microbes, and
thus NK cells provide early defense against intracellular
microbial infections.

34
Q

What are innate lymphoid cells (ILCs)?

A

Populations of lymphocytes that lack TCRs but produce cytokines similar to those
that are made by T cells.

35
Q

Innate lymphoid cells are classified into three groups which produce three different cytokines. What are these cytokines?

A

IFN-γ, IL-5 and IL-17.

36
Q

Fill in the gap:

NK cells are related to group … innate lymphoid cells (ILCs) based on their production of …

A

1, IFN-γ

37
Q

Innate lymphoid cells (ILCs) mostly reside in tissues. What does this say about their function?

A

They probably provide early defense against infections in tissues, before T cells are activated and can migrate
into tissues.

38
Q

Dendritic cells are located at the right place to capture antigens. What places are the right place for this?

A

Under epithelia and in the intestitia of all tissues.

39
Q

What are Langerhans cells?

A

Dendritic cells in the epidermis.

40
Q

What kind of receptors for capturing and responding to microbes do dendritic cells have?

A

Receptors like TLRs and C-type lectin receptors.

41
Q

What are plasmacytoid dendritic cells?

A

Dendritic cells that resemble plasma cells. These cells are present in the blood and lymphoid organs and are major sources of the anti-viral cytokine type I interferon.

42
Q

Where are follicular dendritic cells (FDCs) located and what kind of receptors do they have?

A

They are present in the germinal center of lymphoid follicles in the spleen and lymph nodes. FDCs have a Fc receptor for IgG and receptor for C3b.

43
Q

What is the function of follicular dendritic cells?

A

They can trap antigens bound to antibodies or complement proteins. They display antigens to B lymphocytes in lymphoid follicles and promote antibody responses.

44
Q

What is concentrated in the peripheral lymphoid organs?

A

Antigens, APCs and lymphocytes.

45
Q

As APCs reside in lymph nodes, how are they able to recognise antigens?

A

Because of the fact that lymph passes through lymph nodes, resident APCs are then able to sample antigens that are carried to the lymph node in lymph fluid derived from interstitial fluids of tissues.

46
Q

What’s the role of the spleen in immune responses?

A

As blood enters the spleen it flows through a network of sinusoids which enables the trapping of bloodborne antigens by resident DCs and macrophages. The spleen is therefore important in the immune respons to bloodborne antigens.

47
Q

What is the function of the cutaneous and mucosal lymphoid systems?

A

They are located under the epithelia of the skin and the gastrointestinal
and respiratory tracts. They respond to antigens that enter through breaches in the epithelium.

48
Q

B cells are concentrated in follicles (located around the cortex of a lymph node). What happens if the B cell has come in contact with an antigen?

A

The follicle develops a central pale-staining region called the germinal center.

49
Q

Where are T lymphocytes concentrated in lymphoid nodes?

A

In the parafollicular cortex

50
Q

What kind of APCs reside in the follicles of the germinal center and in the paracortex?

A

The follicles of the germinal center contain follicular dendritic cells that are involved in B cell activation and the paracortex contains dendritic cells that present antigens to T lymphocytes.

51
Q

Where are T and B cells located in the spleen?

A

T cells are concentrated in the periarteriolar lymphoid sheats surrounding small arterioles and B cells reside in the follicles.

52
Q

What type of lymphocytes constantly circulate through peripheral lymphoid organs in order to bind antigens?

A

Naive lymphocytes.

53
Q

Why do effector T cells need to move to the site of infection in order to be able to help, but plasma cells don’t?

A

Plasma cells do not need to
migrate to sites of infection because they secrete antibodies
that are transported via the blood and lymph to distant
tissues.

54
Q

Why are cytokines also called interleukines?

A

Because they have an important role in communication between leukocytes.

55
Q

For what function (and in what manner) are cytokines produced during innate immune response?

A

Cytokines are produced rapidly after microbes and other stimuli are encountered and function to induce inflammation and inhibit virus replication.

56
Q

What are the major sources of cytokine production for the innate immune respons? Name cytokines that ‘belong’ here.

A

Macrophages, DCs, ILCs and NK cells (but endothelial and epithelial cells also), produce TNF, IL-1, IL-12, type IFNs, IFN-γ and chemokines.

57
Q

For what function (and in what manner) are cytokines produced during adaptive immune response?

A

CD4+ T lymphocytes activated by antigens and other signals, produce cytokines and function to promote lymphocyte proliferation and differentiation and to activate effector cells.

58
Q

Name cytokines that ‘belong’ to the adaptive immune response.

A

IL-2, IL-4, IL-5, IL-17 and IFN-γ. (Also TGF-β and IL-10 but they terminate reactions).

59
Q

What are colony-stimulating factors?

A

Cytokines that stimulate hematopoiesis (they stimulate formation of blood cell colonies from bone marrow progenitors).

60
Q

What is the function of colony-stimulating factors?

A

To increase leukocyte numbers during immune and inflammatory responses and to replace leukocytes that are consumed during such responses.

61
Q

By which cells are colony-stimulating factors produced and what are examples?

A

They are produced by marrow stromal cells, T lymphocytes, macrophages etcetera. Examples include GM-CSF and IL-7.