T-cells

Lecture 24.04.2019

• T-cell-mediated immunity

• T-cell regulation

• T-cell development

Monika Raulf

→ gd-T-cells

→ ab-T-cells = Main players of the cellular immune defence

→ killing (killer cells) somatic cells that are affected by a virus or malignant degenerated (e.g. tumour cells)

→ release messengers (cytokines)

Subgroups of T-cells due to gene expression patterns

Surface molecules

CD4-cells CD8-cells

Th1 Th2

Tasks of the T-cells

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TCR: ab-heterodimer

extracellular domain

⇒ Homologous to Immunglobulins

⇒ constant and variable region

TCR = defines the antigen specificity CD3 = is necessary for the transport of the whole complex to the cell surface as well as for the signal transduction after cell activation

Modell of TCR and the associated CD3-complex

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TCR rearrangement

TCR located on chromosome 14 (in humans) Locus: 70 Va + 61 Ja genes + 1 Ca-Gen more than 100 Kb

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Destiny of the thymocytes

Double negative T-cells rearrange their g-, d- and b-genes

g d

g:d TCR b

pTa

Prä-TCR

g:d TCR Prä-TCR

The g:d-T-cell receptor sends out signals, which switch off the b-chain-gene and allocate the cell to the g:d-cell line

g:d TCR

The g:d-T-Zelle maturates and moves in the periphery

g:d TCR Prä-TCR

The pre-T-receptor sends out signals, which switch off the g- and d-chain-genes and allocate the cell to the a:b-cell line

a:b TCR

Based on the gene rearrangement of the a-chains of the T-cell receptor the mature a:b-T-cell receptor arise

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T-cell development in the thymus

Origin: hematopoietic progenitor cell -multipotent-

DN1

multipotent flexible

Final aim: T-cell

DN2

TCR-genes of the d-, g- and

b-loci are restored

complete restored TCR-genes but only

1/3 of all rearrangements are productive

(+), i.e.

β + γδ β - γδ β + γδ β - γδ

DN3

DN4

in proteins adapted

b-chain + invariant pre T cell a-molecule + CD3-signal complex

CD4+ CD8+

TCR a-genes restore and express the mature ab-TCR

exists the thymus

Th1

Th2

peripheral lymphatic

organ

Leave the thymus without repertoire-selection

γδ are CD4

CD8 DN4

γδ

CD4+

CD8+

mature to

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T-cell-mediated immunity

Development of the T-cells in the thymus completed mature T-cells

in blood circulating

arrive at the peripheral lymph organs/ lymph tissues

naive T-cells

until they detect their specific antigen on APC-cell

proliferation and differentiation of the naive T-cell

Daughter cells = armed T-effector cells contribute to the disposal of the antigens

prim

ary

imm

une

resp

onse

can act on the target cell Monika Raulf 7

Cell contact with non-antigen specific interaction Requirement: complementary disposal of adherence molecules

Selectins, integrins and members of the immunoglobulin superfamily are important (see also movement of the monocytes/neutrophils)

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Movement, activation and effector function of the lymphocytes depend on the adherence molecules

Stabilisation of the connection between T-cell and APC via specific antigen recognition

LFA-1 = lymphocyte function-associated antigen-1

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The activation of T-cells modifies the expression of some cell surface molecules

Cell surface molecules

CD4- T-cell

L-selectin (CD62L) VLA-4 LFA-1 CD2 CD4 T-cell

receptor CD44 CD45RA CD45RO

inactive + - + + + + + + -

active - + ++ ++ + + ++ - +

from: „Immunologie“, Janeway et al.

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Co-stimulatory interaction between T-cell and APC

CD80 /CD86 belong to the B7-molecules; interact with CD28 and effect the clonal proliferation of the T-cells

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“immunological zip“ T-cell B-cell

Anergy – antigen recognition without co-stimulation

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from: „Immunologie“, Janeway et al.

Microbial substances can cause a co-stimulating activity in macrophages

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CD4 & CD8 bind on MHC

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“The immunological zip”

Cytotoxic T-cell Helper T-cell

APC target cell

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Cell-cell adherence molecule - binds on MHC class II and

stabilizes the TCR/MHC complex

- binds on the β2 domain of the MHC protein

• CD4 transduces signals in the T-cell

• CD4 is a receptor for HIV

Helper T-cell

APC

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• Exists of two α-chains or of αβ-chains

• CD8 is an cell-cell adherence molecule

• CD8 transduces signals in the T-cell

Cytotoxic T-cell

target cell

The three most important T-effector cells synthesize different effector molecules

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The different stages of the activation of CD4-T-cells

TH1-cell TH2-cell

Activation of macrophages; B-cells produce antibodies of the

isotype IgG1

Activation of B-cells, they produce antibodies of IgE, IgG4; activation of

eosinophilic granulocytes

from: „Immunologie“, Janeway et al.

Naive CD4-T-cell (uncommitted)

Activated proliferating T-cell

Activated T-cell not determined (TH0)

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At least four different groups of CD4+ regulatory T-cells play, e.g. for asthma bronchial, a role

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“Adaptive Treg“

“Naturally occurring“ Treg

TH1 T-bet

STAT-4

TH2 GATA-3 STAT-6

TH17

RORγT

Treg

Foxp3

IL-6

IL-27

TGF-β IL-23 TNF

γ-IFN, TNF

IL-4

IL-17

TGF-β

TH

IL-4

IL-12

Differentiation and regulation of T-helper cells

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Functionally T-cell population

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Example how the Th1-/Th2-difference has an effect on the course of an infection

Lepra

tuberculoid lepra lepromatous lepra

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Lepra Mycobacterium leprae-infection

M leprae grows in macrophage vesicles; macrophages are activated by Th1-cells; just a few bacteria measurable, just a few antibodies; inflammation damages skin and peripheral nerves; patient survives mostly

Antibody-development by humorale reactions, activated by Th2-Zellen; antibodies cannot reach bacteria in the macrophages, can breed unimpeded; Result: widespread, most lethal tissue destruction

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Example how the Th1-/Th2-difference has an effect on the course of an infection

tuberculoid lepra lepromatous lepra

Cytokines

are the hormones of the immune system

they exert their effect through cytokine receptors

they are pleiotropic, meaning one cytokine is able to induce different effects; has different features

they mediate the most different processes in the immune system

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Cytokine-receptor

Cytokine

Production site of the cytokines and chemokines

APZ IFN-a, TNF-a, TGF-b, IL-1, IL-6, IL-8, IL-10, IL-12, MCP-1, MIP-1, GM-CSF, M-CSF

T-cells IL-2, IL-3, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13, IL-15, GM-CSF, IFN-g, TNF-b, MIP-1b, RANTES, TGF-b

B-cells Mast cell

TNF-b, MIP-1b IL-12

IL-4, IL-5, CD40-ligand

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Natural immunity

IFN-a, TNF-a, IL-1, IL-6, IL-8

APZ B-cell

Activation, growth, differentiation lymphocytes

IL-2, IL-4, TGF-b, IL-10

Eos

Activation inflammation cells

IFN-g, IL-5, IL-9, MIF

Activation hematopoiesis

IL-3, GM-CSF, M-CSF, IL-7

T-cell

Neut Native cell

Functional classification of cytokines

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CD4/Th1

CD40-ligand

cytokines others

IFN- g GM-CSF TNF-a

CD40-ligand Fas-ligand

IL-3 TNF-b (IL-2)

one reason: IFN-g inhibits the proliferation of Th2-cells

Cytokines, which are build in the early phases of an infection, influence the functional differentiation of CD4-T-cells

In presence of IFN-g and IL-12 promote the development of Th1-cells

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CD4/Th2

CD40-ligand

cytokines others IL-4 IL-5

CD40-ligand

IL-3 GM-CSF

Development of Th2-cells

IL-10, IL-4 and TGF-b inhibit the activation and proliferation of Th1-cells

In the presence of IL-4* and also IL-6 active CD4-cells develop to Th2-cells

* IL-4 originate potentially from NK1.1+-T-cells (subgroup of the CD4-positives)

CD4/Tr1**

** T regulatory 1 cells

IL-10 TGF-b

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Th2-cells activate, especially at primary reactions, highly effective B-cells. Th1-cells are in contrast crucial for the macrophage activation. Also at CD8-T-effector cells there are respective subpopulations (Tc1 or Tc2).

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Species and amount of the antigen peptides can also influence the differentiation of CD4-T-cells

Low affinity

naive T-cell Th2

Minor density of peptides on the surface of APC induce Th2-response, also peptides, which bind just weak on the TCR

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High affinity

naive T-cell Th1

High density of peptides on the surface of APC induce Th1-response, also peptides, which interact intensive with the TCR.

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Nomenclature and functions of well characterised T-cell cytokines I

Cytokine T-cells (source)

Effect on Effect of the gene-knock-

out B-cells T-cells Macro-phages

Haemato-poietic cells

Other somatic

cells

Interleukin-2 (IL-2)

TH0, TH1, some CTL

stimulates growth and synthesis of

the J-chain Growth __ stimulates growth

of the NK-cells __ ↓ T-cell-responses, IBD*

Interferon-g (IFN-g) TH1, CTL Differentiation;

IgG2a-synthesis

inhibits the growth of TH2-cells

Activation, ↑ MHC-class I and

MHC-class II activates NK-cells

anti viral; ↑ MHC-class I and

MHC-class II

susceptible to mycobacteria

Lymphotoxin (LT, TNF-b)

TH1, some CTL inhibits kills

activates, induces NO-production

activates neutrophils

kills fibroblasts and tumour cells

Lymph nodes are missing, spleen

structure abnormal

Interleukin-4 (IL-4) TH2

Activation, growth, IgG1, IgE, ↑

induction of the MHC-class II

Growth, survival

inhibits macrophage-

activation

↑ Growth of mast cells __

no TH2

Interleukin-5 (IL-5)

TH2

Differentiation, IgA-synthesis

__

__

↑ Growth and differentiation

__

__

Interleukin-10 (IL-10) TH2 ↑ MHC-class II inhibits TH1 Inhibits release

of cytokines

co-stimulates the growth of mast

cells

__

IBD

from: „Immunologie“, Janeway et al. *IBD = inflammatory bowl disease

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Cytokine T-cells (source)

Effect on Effect of the gene-knock-

out B-cells T-cells Macrophages Haemato-poietic cells

Other somatic cells

Interleukin-3 (IL-3)

TH1, TH2, some CTL

__

__

__

Growth factor for precursor

haematopoietic cells (multi-CSF)

__ __

Tumour necrosis-factor-a (TNF-a )

TH1, some TH2

and CTL

__

__

activates, induces NO-production

__

activates micro-vascular

endothelia

Resistance against gram-

negative sepsis pathogens

Granulocyte-macrophage-colony stimulating factor (GM-CSF)

TH1, some TH2

and CTL

Differentiation inhibits growth

Activation, differentiation to dendritic cells

↑ Development of granulocytes and

macrophages (myelopoiesis) and

dendritic cells

__

__

Transformation of the growth factor b (TGF-b )

CD4-T-cells

inhibits growth; factor for the IgA-class switching

__

inhibits activation activates neutrophils

inhibits/ stimulates cell

growth

Death after approximately

ten weeks

from: „Immunologie“, Janeway et al.

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Nomenclature and functions of well characterised T-cell cytokines II

Cytokine receptors belong to several families of receptor proteins, which have each different structures

Cytokine receptors of class I (family of the erythropoietin receptors)

Receptors for erythropoietin, growth hormone and IL-3

Receptors for IL-3, IL-5 and GM-CSF have the same chain, CD131 or bc (same b-chain)

Receptors for IL-2, IL-4, IL-7, IL-9 and IL-15 have the same CD132- or gc-chain (same g-chain); IL-2-receptors have besides a third chain, a high affinity IL-2Ra-(CD25-) subunit

Cytokine receptors of class II

Interferon-a, -b- and -g-receptors, IL-10-receptor

Family of the TNF-receptors

Receptors I and II for the tumour necrosis factor (TNF); CD40, Fas (Apo1), CD30, CD27, receptor for the nerve growth factor

Family of the chemokine receptors

CCR1-5, CXCR1-4

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Th0

Th2

Th1 Monocyte

IL-12 IFN-g

+

+

Mast/Baso

IL-4

IL-4 / IL-10 IL-12 / IFN-g

-

Allergens

Infections

Lectine

Genes

IL-3, IL-4, IL-5 IL-13, GM-CSF TGF-b

IL-2, IFN-g, TNF-a, GM-CSF

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The immune response against intracellular bacteria is coordinated by activated TH1-cells

activated TH1-cell

IFN-g and CD40- ligand

activates macrophages to eliminate absorbed bacteria

Fas-ligand or TNF-b

kills chronic infected cells; bacteria are

released to be eliminated by

new macrophages

IL-2

Induces a proliferation of T-cells,

whereby the amount of

effector cells increases

IL-3 + GM-CSF

induces in bone marrow

the differentiation of macropha-

ges

TNF-a + TNF-b

activates the endothelia that macro-phages bind

on it and leave the

blood vessel at the site of

infection

MCP-I

Motivates macrophages to accumulate at the site of

infection

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T-effector cells regulate effectively all known effector mechanisms of the

acquired immune response

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Immune protection is ensured both by existing reactants and immunological memory

First immune reaction

Protective immunity

Immunological memory

First infection Symptomless re-infection Easily

proceeding or symptomless re-

infection

Day 1 to 42 Year 1 to 4

T-cells and antibodies

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Immunological processes of an infection Adhesion to the

epithelia Local infection, transition of the

epithelia

Local infection of the tissue

Proliferation in the lymph system

Adaptive immune response

Normal flora Local chemical

factors Phagocytosis

(especially in the lung)

Wound healing Anti bacterial proteins and

peptides Phagocyte g-d T-cells

Complement (alternative way),

Phagocytes, Cytokines, NK-cells,

Activation of macrophages

Phagocytes, Capture of antigens, NK-cells

Specific antibodies,

T-cell-dependent activation of the macrophages,

cytotoxic T-cells

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The broad spectrum of different pathogens has led to the evolutionary development of two key features of adaptive immunity:

A) Development of an even greater variety of B and T cell receptors

B) According to the different living environments and lifecycles of pathogens, a whole range of different effector mechanisms has developed

If every host were killed quickly after being infected by a pathogen, it would not be as beneficial for the survival of the pathogen in the long term as its rapid destruction by the immune system, even before it could multiply (Modus Vivendi).

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After the removal of the infection most of the effector cells die (the antibody levels decrease in parallel) (negative feedback) and memory cells occur.

Apoptosis of most of the effector cells.

Nevertheless, some cells survive and deliver the raw material for memory cells and the reactions of the B-cells

Immunological memory = ability of the immune system to react faster and more effectively to pathogens it has previously encountered (e.g. vaccination)

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Immunological memory It is most likely to be sustained by long-lived antigen-specific lymphocytes, which are activated by the first contact and are maintained until they encounter the pathogen a second time.

It is believed that most memory cells are in an inactive state, but a small percentage undergoes division at certain times; IL-15 could be a stimulus

T memory cells have different surface proteins compared to armed T effector cells (e.g., they do not express CD69, but larger amounts of the Bcl-2 protein, which promotes cell survival, increases the expression of CD44 on the surface).

CD4-cells can differ into two types of memory cells:

a) Effector-memory cell (CCR7-neg.), b) Central memory cell (CCR7-pos)

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