Evgeniya Solodova01.12.08

Introduction:

Regulatory cytokine transforming growth factor-β (TGF-β):

- is a secreted protein that exists in three isoforms called TGF-β1, TGF-β2 and TGF-β3

- TGF-β1 is the founding and predominant member of this family

- controls proliferation, differentiation, and other functions in many cell types

- acts as a negative autocrine growth factor

- specific receptors for TGF-β activation trigger apoptosis when activated

- many cells synthesize TGF-β and almost all of them have specific receptors for this peptide

T lymphocytes are the key components of the adaptive immune system

- express T cell receptors (TCR) which recognize antigens in association with molecules of MHC

- selected in the thymus according to the affinity to self-antigens to prevent auto immune response

- differentiate upon infection into effector T cells – CD4+ helper T cells or CD8+ cytotoxic T cells – to combat the invading pathogen

Introduction:

All these crucial processes of T cell development, homeostasis, tolerance to self antigens and differentiation are highly dependent on TGF-β regulation

Understand the regulation of T cells by TGF-β

Synthesized in inactive form in association with latency-associated protein (LAP)Synthesized in inactive form in association with latency-associated protein (LAP)

Secreted as such Bind to latent-TGF-β-binding protein (LTBP) targeting TGF-β to ECM

cells that produce TGF-β activator can differ from those that secrete TGF-β integration of signals from multiple cell types to regulate cellular responses

- Binding to complex of TGF-β type I (TGF-βRI) and type II (TGF-βRII) receptors active signalling pathways

- Phosphrilation of transcriptional factorsSmad2 and 3 translocation to the nucleus with Smad4 or TIF1γ

- Binding to the regulatory sequences intarget genes regulation of gene expression

OR

- Activation of Smad-independent signalling pathways

The plasticity of Smad proteins in transcriptional regulation

and the diversity of Smad-independent pathways enable

TGF-β to exert its pleiotropic actions

TGF-β Regulates T Cell Development

Using different mice models (TGF-βRII- and TGF-βRI-deficient mice, TGF-βRII-deficient H-Y TCR transgenic mice) it was shown that TGF-β signalling in T cells :

- promotes CD8+ and CD1d-dependent natural killer (NKT) T cell differentiation

- reveals opposing functions on the CD4+Foxp3+ regulatory T (nTreg) cell development depending on the mice age

TGF-β regulates naive T cell homeostasis

• TGF-βRII-deficient OT-II cells (T cell TCRs have high binding affinity only to non-self MHC II antigen) undergo a high cell death and are largerly depleted in peripheral lymphoid organs

• Lack of TGF-β signalling in CD8+ cells in H-Y TCR-transgenic mice led to diminished mature T cell numbers in female mice

TGF-β signalling in T cells is essential for maintaince of peripheral T cell tolerance

- How TCR specificity modulates T cell responses in TGF-β-deficient mice or mice with T cell-specific inactivation of TGF-β receptors?

- What is the reason for naive T cell loss when TGF-β signalling is disrupted?

TGF-β regulates naive T cell homeostasis

In OT-II mice, deficient for Tgfbr2 gene, T cells actively differentiate into T helper 1 (Th1) or Th2 effector T cells, in contrast to normal polyclonal T cell population

TGF-β-deficient mice with other single nonself TCR affinities (TEα transgenic T cells and DO11.10 T cells)

Th1 cells secrete IFNγ and lymphotoxin to combat intracellular pathogens through activation of adaptive immune system

Th2 cells produce IL-4, IL-5 and IL-13 which direct antibody production to control extracellular pathogens

• TGF-β may have an essential role in promoting the survival of both CD4+ and CD8+ naïve T cells that interact with low

affinity to self-antigens

• Modulates immune tolerance by inhibiting high-affinity CD4+ and CD8+ T cell proliferation and differentiation into

Th1 and Th2 and cytotoxic T lymphocytes

• Active immune suppression by cytokine TGF-β1 or CD4+Foxp3+ Treg cells is a pivotal mechanism of peripheral T cell tolerance

• Mice lacking either TGF-β1 or Foxp3, the transcription factor required for Treg cell function, develop multifocal inflammatory disorders

What is the mechanism underlying TGF-β regulation of T cell tolerance?

TGF-βRII-, TGF-β1-deficient mice, bone marrow chimera and T cell transfer experiments

Lack of TGF-β signalling leads to:

-Reduction of nTreg cell -More activated and differentiated phenotype of T cell populations

T cells

thymic nTreg cells

Foxp3 expression

TGF-β• recruiment of downstream transcriptional factor Smad3 to aFoxp3 enhancer element

• T cell produced IL-2 activates STAT5 for binding to Foxp3 promoter

Differentiation of iTreg cells

induced Treg (iTreg) cells in periphery

T cells

thymic nTreg cellsthymic nTreg cells

Foxp3 expression

TGF-β• recruitment of downstream transcriptional factor Smad3 to aFoxp3 enhancer element

• T cell produced IL-2 activates STAT5 for binding to Foxp3 promoter

Differentiation of iTreg cells

RORγt expression

induced Treg (iTreg) cells in periphery Th17 cells

• IL-6 activates STAT3 induction of ROPγt expression

Differentiation of Th17 cells

Th17 cells secrete IL-17A, IL-17F, IL-22, that act on a broad range of innate immune and nonhematopoietic cells to protect the host from extracellular pathogensRORγt - - transcription factor that orchestrates the differentiation of Th17 lineage

• Foxp3 interacts with ROPγt and suppresses its functionmechanism for reciprocal differentiation of iTreg and Th17 cells

TGF-β

TGF-β i inhibits Th1, Th2 and CTL proliferation and differentiation

• Block of TCR-induced Tec kinase Itk activation and Ca2+ influx in T cells

• Downregulation of NFAT, T-bet and GATA-3 expression

• Inhibition of IL-2, IFNγ and granzyme B transcription viaassociation of TGF-β with Smad2/3 complexes

Inhibition of Th1, Th2 and CTL cell proliferation and differentiation

Itk kinase - Interleukin-2 inducible T-cell protein tyrosine kinaseNFAT - Nuclear factor of activated T-cells Th1 - specific T box transcription factor granzyme B - granzyme 2, cytotoxic T-lymphocyte-associated serine esterase 1

TGF-β engages multiple signalling pathways to control T cell development

A Three-Cell Model for TGF-β1-Dependent Regulation of T cells

• Antigen recognition and Antigen recognition and presentation by DCspresentation by DCs

• Activation of Treg cellsActivation of Treg cells

• Production of latent form of TGF-Production of latent form of TGF-β1β1

• Association with LAP (and LTBP)Association with LAP (and LTBP)

• Activation and release of TGFActivation and release of TGF-β1-β1

• Inhibition of CD4+ T cell Inhibition of CD4+ T cell differentiation into Th1 and Th2 cellsdifferentiation into Th1 and Th2 cells

• Promotion of CD4+ T cell Promotion of CD4+ T cell differentiation into iTreg or Th17 cellsdifferentiation into iTreg or Th17 cells

• Low production of TGF-β1 by activated CD4+ T cells that potentially regulates T cell Low production of TGF-β1 by activated CD4+ T cells that potentially regulates T cell differentiation through an autocrine routedifferentiation through an autocrine route

Summary and Future Perspectives

regulates thymic T cell development and peripheral T cell survival, proliferation and differentiation

ensures the maintenance of divers and self-tolerant T cell repertoire and the initiation of appropriate T cell responses essential for an effective adaptive immune system

may have an important role in more ancient biological processes such as embryonic development and carcinogenesis

New insights into the control of T cell responses by TGF-β will help to illuminate the fundamental principles of T cell regulation and facilitate the employment of TGF-β to treat a variety of immune-related disorders

TGF-β:

Thank you for your attention!Thank you for your attention!