The adaptive Immune

response

22. May 2019, Ruhr-Universität Bochum

Marcus Peters, marcus.peters@rub.de

Activated Lymphocyte in blood

All T-lymphocytes are derived from

hematopoethic stem cells from the

bone marrow

Rearrangement of TCR genes in the genome

b-chain a-chain

V-segments 52 70

D-segments 2 0

J-segments 13 61

Combinatorial diversity 5,7 x 106

Total diversity 1016

Diversity of T-cell receptors

Which strategies exist to avoid

recognition of self-antigens?

Selection of T-lymphocytes in the Thymus---Central Tolerance

Negative selection of T-lymphocytes binding to self antigens with high affinity

Cells binding to self antigens die by apoptosis

Positive selection on ability of binding to MHCI and MHCII molecules

Cells with no affinity to MHC die by apoptosis

Immature DCs are specialized in engulfment of

antigens and present peptides of the digested

proteins on MHC molecules

Presentation of antigen by dendritic cells

MHC class I MHC class II

Expression by cell type all nucleated cells on antigen presenting

cells

Interaction with T-cell

subsets

CD8 cytotoxic T-cells CD4 T-helper cell

Molecular structure a-chain associated with

b2-microglobulin

a-chain associated with

b-chain

Peptides presented 8-10 amino acids larger than 13AA

Intracellular Location Endoplasmatic Reticulum Endosomes

Characteristics of MHC molecules

On MHC class I peptides were presented that are

derived from intracellularly synthesized proteins

Virus infecting

cell

Presentation of peptides on MHC I to T-

Lymphocytes

Peptide

Cell membrane

Cell membrane

Extracellular Proteins

engulfed by antigen

Presenting cell

APC

On MHC class II peptides were presented that are

derived from extracellular sources

Presentation of peptides on MHC II to T-

Lymphocytes

Peptide

Cell membrane

Cell membrane

Anergy: Recognition of antigen without costimulation

Peripheral Tolerance 1

APC APC

T-helper-cell Cytotoxic T-cell

Interaction between LFA-1 and ICAM-1 leads to

stabilization of interaction between T-cells and

Antigen Presenting Cell (APC)

Interaction between CD4 and MHCII or CD8 and MHCI

amplifies the signal given by interaction of the MHC-Peptide

complex with the TCR

Interaction of Co-stimulatory molecule

CD80/86 with CD28 is essential for optimal

activation of effector T-cells

Effector mechanisms of activated T-lymphocytes

Th0

Th2

Th1

+

Mast/Baso

IL-4

DC

IL-12

+

IL-4

IFN-g

Differentiation of Th1 or Th2 lymphocytes

Th0

Th2

Th1

+

Mast/Baso

IL-4

DC

IL-12

+

IL-4

IFN-g

-

-

Negative Feedback Regulation

The immune response to cells infected with bacteria

is coordinated by Th1 Lymphocytes

activated TH1-cell

IFN-g

Activation of

macrophages

leading fusion

of lysosomes

and

phagosomes

Fas-Ligand

oder TNF-b

Killing of

infected cells

by apoptosis

IL-2

Autocrine

mechanism

proliferation

of T-cells

IL-3 + GM-

CSF

Generation of

macrophages

and DCs in

bone marrow

TNF-a

Activation of

endothelium

to attract

macrophages

TH2-cells are important for amplification of B-cell responses

and involved in defense against parasites

activated TH2-cell

Autocrine

stimulation of

T-cell

proliferation,

paracrine

stimulation of

B-

lymphocytes

IL-4

Activation of

B-lymphocytes

Isotype switch

to IgG4 and

IgE, triggering

of Th2

immunity while

suppression of

Th1 immunity

Proliferation

and activation

of eosinophilic

granulocytes

Regulation of

immune

response

IL-2 IL-5 IL-10 IL-13

Activation and

proliferation of

B-lymphocytes

But in the last years several new

subpopulations of T-helper cells were

described….

Th0 Th17 IL-17+

IL-6

TGFb

IL-23

IL-8IL-6

Neutrophilic

Granulocytes

Th17 cells are important for elimination of

fungal infections

Fibroblast IL17R

Th0 TregIL-10

TGF-b

+

IL-10

Regulatory T-helper cells are important for

down regulation of the immune response

Peripheral Tolerance 2

Inflammation ↓

T-cells ↓

O´Shea&Paul 2010. SCIENCE 327:1098

23

• B-cells develop continuously in the

bone marrow, they derive from

lymphatic progenitor cells

B-cell development

• The environment (stromal cells of the

marrow) delivers the necessary

milieu (surface molecules and

cytokines) for the development

• The immunoglobulin genes are

rearranged

24

Somatic recombination

Combinatorial diversity:

Light chain : 40 VL-segments

5 JL-segments

40 x 5 = 200

25

Combinatorial diversity:

Heavy chain:

51 VH-segments

27 DH-segments

6 JH-segments

51 x 27 x 6 = 8262

8262 heavy chains

Somatic recombination

26

200 light chains x 8.262 heavy chains = 1,6 x 106

Somatic recombination

27

Junctional diversity

At the junction of the gene segments

nucleotides are introduced by the

enzyme Terminal deoxynucleotidyl

transferase TdT (N-nucleotides).

Due to this process there is a high chance

for the induction of frame shift mutation!

During VDJ recombination the

enzyme recombination activating

gene (RAG1&2) induces palindromic

nucleotides (P-nucleotides)

28

Somatic hypermutation

Affinity maturing of the antigen binding sites takes place in the

secondary lymphatic organs (only in activated B-cells).

Mutations occur in the whole variable region of the antibody.

Mutations appear in certain regions (hot spots).

The mechanism of the somatic hypermutation is mostly

unknown.

B cells become apoptotic when somatic hypermutation

resulted in reduced binding affinity of the antibody (during

affinity maturation)

29

Summary

Antibodies can be raised against almost every molecule

The antibody diversity is based on three different

mechanisms:

1) Combinatorial diversity

(Somatic recombination)

2) Junctional diversity

(Inaccurate junction)

3) Somatic hypermutation

(Affinity maturation in germinal centres)