Cellular and Molecular Immunology

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Cellular and Molecular Immunology Peripheral B
and T cell differentiation Christoph Mueller
Institute of Pathology christoph.mueller_at_pathology
.unibe.ch

• General principles
• - functional subsets
• - plasticity vs. stability of phenotype
•   Molecular basis of lymphocyte differentiation
• transcription factors
• Soluble factors and cognate interactions
  involved in
• the differentiation of lymphoid cells
• Experimental approaches to study B/T cell
  differentiation
•    Consequences of impaired T and B cell
  differentiation

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RAG-1, 2

• RAG1 and RAG2 (Recombination Activation
  Genes) are essential for the rearrangement of
  the Ig and TCR genes
• Mice deficient for either RAG1 and/or RAG2 are
  deficient for both T and B cells (but may still
  have some NK cells)
• to prevent the later generation of autoreactive
  T and B cells, the expression of these two
  genes needs to be tightly regulated

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Regulation of T cell receptor gene
rearrangement Experimental approach for
determining the regulation of RAG gene
expression
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Experimental set-up

• Mouse, transgenic for TCRab, recognizing the LCMV
  peptide gp33 in the context of H-2 Db
• In a C57BL/6 (H-2b) genetic background positive
  selection of TCRab tg T cells, tg TCRab expressed
  on thymocytes)
• - In a BALB/c (H-2d) background (no positive
  selection of TCRab tg T cells no tg TCRab
  expressed on thymocytes)

Working hypothesis recognition of a MHC/Ag
complex via a positively selecting TCRab
down-regulates RAG expression in the
differentiating T cells, and thus, terminates
TCRab rearrangements
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Cortex
Medulla
In situ hybridisation for the detection of RAG-1
mRNA Thymus, wild type mouse (C57Bl/6 mouse)
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Medulla
Cortex
Murine Thymus, TCRab tg mouse with a positively
selecting MHC haplotype transcription of RAG1
gene is suppressed
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Cortex
Medulla
Murine Thymus, TCRab tg mouse with a non -
selecting MHC haplotype transcription of RAG1
gene is still active in the cortex
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CD8 T cell differentiation
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Functional Heterogeneity of CD4 T Lymphocytes

• naive CD4 T Cell

Th0
Th2
Th1
ThO IL2, IL3, IL4, IL5, IL6, IL9, IL10,
IFN? Th1 IL2, IFN? , TNF????lymphotoxin Th2 IL
4, IL5, IL6, IL9, IL10
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Naïve CD4
IL 12
IL 4
IFN g
Th 1
Th 2
Grogan Locksley Curr Opinion Immunol 14
366-72 2002
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Leprosy

• Chronic - progressive infectious disease,
  affecting the skin, peripheral nerves and
  occasionally the respiratory tract
• Infectious agent Mycobacterium leprae
• Globally, approx. 10-20 million patients
  infected, endemic in tropical areas (e.g.
  Southeast Asia India, South America, Subsaharan
  Africa)

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Leprosy Prevalence
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Leprosy different clinical forms of the disease

• Lepromatous Leprosy
• Multiple, nodular lesions of the skin, in
  particular, of the face (lion face").
• Persistent bacteriemia, foamy cell-like lesions
  with numerous M. leprae present
• Tuberculoid Leprosy
• Singular, small macular lesions of the skin.
• Peripheral nerves (e.g. N. ulnaris, peronealis,
  N. auricularis) are often affected
  sensory neuropathy.
• Granuloma are frequent (with only low numbers of
• M. leprae present)

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Immunological Spectrum of Leprosy
Tuberculoid leprosy Lepromatous
leprosy Granuloma formation Persistence of
M. leprae Tissue damage may ensue Disfiguring
disorder
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Tuberkuloid leprosy
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Type IV Hypersensitivity reactions
Fig. 5-11 Kumar 6th edition
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Pathogens may influence the resulting adaptive
immune response
Science 302 993-4 2003
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Figure 1 Stimulating the Th1 or Th2 response. In
both pathways, dendritic cells internalize the
pathogen. They present its antigens to T cells,
which recognize antigens through their T-cell
receptors (TCR). a, Organisms such as
intracellular bacteria or viruses are recognized
by the Toll-like receptors on dendritic cells
the resulting signals induce the secretion of
interleukin-12 (IL-12) and differentiation of CD4
T cells into the Th1 lineage that produces gamma
interferon (IFN-). b, How dendritic cells
recognize larger pathogens, such as parasitic
worms, is not known. But the end result is
differentiation of Th2 effector cells regulated
by T-cell-produced interleukin-4 (IL-4).
Information1, 2 on the link between dendritic
cells and T cells suggests that the former
express different Notch ligands Delta or Jagged
under different conditions. Jagged is
specifically induced by stimuli known to induce
Th2 differentiation. Notch signals (Notch-IC) can
induce transcription of IL-4 through direct
binding of RBPJ to the IL-4 promoter1 Nature 430,
150 - 151 (08 July 2004)
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Publications on Suppressor T cells and Regulatory
T cells
1974 1976 1978 1980 1982 1984 1986
1988 1990 1992 1994 1996 1998 2000
2002
300
Suppressor T cells
250
200
150
Publications per Year (PubMed)
100
50
0
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Rregulatory T cell subsets
Natural regulatory T cells express the
cell-surface marker CD25 and the transcriptional
repressor FOXP3 (forkhead box P3). These cells
mature and migrate from the thymus and constitute
510 of peripheral T cells in normal mice. Other
populations of antigen-specific regulatory T
cells can be induced from naive CD4CD25- or
CD8CD25- T cells in the periphery under the
influence of semi-mature dendritic cells,
interleukin-10 (IL-10), transforming growth
factor- (TGF-) and possibly interferon- (IFN-).
The inducible populations of regulatory T cells
include distinct subtypes of CD4 T cell T
regulatory 1 (TR1) cells, which secrete high
levels of IL-10, no IL-4 and no or low levels of
IFN- and T helper 3 (TH3) cells, which secrete
high levels of TGF-. Although CD8 T cells are
normally associated with cytotoxic T-lymphocyte
function and IFN- production, these cells or a
subtype of these cells can secrete IL-10 and have
been called CD8 regulatory T cells.
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Mechanism(s) of suppression. Various molecular
and cellular events have been described to
explain how Treg can suppress immune responses.
They include IL-2 gene expression inhibition,
modulation of costimulatory molecules on APCs and
interaction of LAG3 with MHC class II molecules
(a), immunosuppressive cytokine secretion (b),
induction of tryptophan catabolism through CTLA-4
(c) and cytotoxicity (d). However, none of those
mechanisms can explain all aspects of
suppression. It is probable that various
combinations of several mechanisms are operating,
depending on the milieu and the type of immune
responses. It is also possible that there might
be a single key mechanism that has not been found
yet (e). Abbreviations APC, antigen presenting
cell TCR, T cell receptor.
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Peripheral naive CD4 T cell precursor cells
(THp) can differentiate into three subsets of
effector T cells (TH1, TH2 and TH-17) and several
subsets of Treg cells, including induced Treg
cells (iTreg), Tr1 cells and TH3 cells. Naturally
occurring Treg cells (nTreg) are generated from
CD4 thymic T cell precursors. The
differentiation of these subsets is governed by
selective cytokines and transcription factors,
and each subset accomplishes specialized
functions.
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CD4 T cell differentiation (for beginners)
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CD4 T cell differentiation (for
specialists) (Keiji Hirota, Bruno Martin and
Marc Veldhoen, 2010)
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B cells .
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CD4 T-Zelle
2.Signal Quervernetzung der Ig durch Antigen
oder Aktivierung durch CD40L
T-Zell-Hilfe durch Zytokine
CD40L
CD40
A
1. Signal Bindung des Antigen an Ig
A
A
2. Signal
kein 2. Signal
naive B - Zelle
B-Gedächtniszelle
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Program of my next lectures

• Molecular mechanisms of immune tolerance
• Central tolerance induction in the B cell and T
  cell compartment
• Immune tolerance in the periphery
• Immunopathology vs. Autoimmunity
• Immune tolerance vs. Immune privilege vs. Immune
  ignorance