Cluster 1: Immune tolerance

Cluster 1: Immune tolerance

Immune regulation: Dr Benedict Seddon

Ben Seddon intro A

What does homeostasis of T cells mean and why is it important to understand how it works?

Ben Seddon A01

What does homeostasis of T cells mean and why is it important to understand how it works?

Ben Seddon A02

The composition of the T cell compartment is heterogenous both in terms of different types of T cells and in their states of differentiation. What is remarkable is that this composition is relatively stable throughout life suggesting that:
1. there must be specific homeostatic mechanisms controlling this composition, and
2. that this is an optimal configuration for effective immunity

Ben Seddon A03

Characterising the mechanisms of T cell homeostasis is important for understanding how the immune system functions normally and how dysfunction results in disease. The key questions my research  programme is addressing are:
1. How are T cells generated in sufficient numbers and in an optimally functional state?
2. How are T cells kept alive and functional between infections?

Ben Seddon A04

Numbers of mature T cells are maintained by balancing cell production, division and death.
We are specifically interested in the role that TCR signals and cytokines play in these processes since they are required throughout a T cell life.

Ben Seddon A05

The key questions my programme is addressing are:
1. How are T cells generated in sufficient numbers and in an optimally functional state?
2. How are T cells kept alive and functional between infections?


Ben Seddon intro B

NF-κB is a transcription factor active in almost all cells of the body. It is required for the normal function of mature T cells.
We have identified an unexpected function for NF-κB signalling during development of new T cells.

Ben Seddon B01

NF-κB is a transcription factor active in almost all cells of the body. It is required for the normal function of mature T cells.
We have identified an unexpected function for NF-κB signalling during development of new T cells.

Ben Seddon B02

We are interested in how homeostatic signalling is transmitted in T cells. The NF-κB family of transcription factors are expressed by most cells of the body and are critical for their survival.

NF-κB is essential for normal immunity, but its functions in T cells are not fully understood.

Ben Seddon B03

Conventionally, it is thought that NF-kB activation in T cells, typically downstream of TCR, regulates cell survival by control expression of pro-survival Bcl2 family members, and production of inflammatory cytokines.

Ben Seddon B04

It is also well recognised that new T cells require maturation in the periphery for many days before they can become fully functional. How this occurs and what signalling pathways are involved is completely unknown.
We have now identified a novel role for NF-κB signalling in the maturation of new T cells, so called ‘recent thymic emigrants’ (RTE).

Ben Seddon B05

We manipulated NF-κB signalling by deleting IKK2, a key component of the IKK complex, causing a partial block in canonical NF-κB signalling.

Ben Seddon B06

We asked when T cells needed IKK2 signalling, by deleting it at different times in development:
– in the thymus, specifically after selection (1)
– or in fully mature peripheral T cells (2)
and then assessed the homeostatic function of mature T cells

Ben Seddon B07

When IKK2 was deleted after T cells had left the thymus and were fully mature (2), their survival and proliferation was normal. IKK2 is not required to transmit survival of proliferation signals to T cells.

Ben Seddon B08


When IKK2 was deleted after T cells had left the thymus and were fully mature (2), their survival and proliferation was normal. IKK2 is not required to transmit survival of proliferation signals to T cells.

Ben Seddon B09

One of the hallmark changes in RTE as they mature is their upregulation of IL-7R. IL-7R is required for normal T cell homeostasis. When IKK2 was deleted in the thymus (1), mature T cells failed to express IL-7R normally.

However, deleting IKK2 in fully mature T cells did not effect IL-7R expression (2). IKK2 signalling is required to switch on IL-7R but not needed to keep it on.

Ben Seddon B10

NF-κB signalling is essential for normal maturation of new T cells. Our work now aims to identify the receptors required to activate NF-κB during development, and whether there are other genes regulated by this signalling.


Ben Seddon intro C

It is becoming easier to generate large volumes of complex data. How can we get the most information out of such datasets?
We have been using mathematical models to help organise data, generate and test hypotheses.

Ben Seddon C01

It is becoming easier to generate large volumes of complex data. How can we get the most information out of such datasets?
We have been using mathematical models to help organise data, generate and test hypotheses. 

Ben Seddon C02

The interplay of cell death, division and differentiation processes that mediate homeostasis within the T cell compartment can result in highly complex cellular behaviour.
To better understand these processes at a System’s level, we work with Mathematicians to develop
models that formalise and test our understanding.

Ben Seddon C03

On successful application of mathematical modelling has been our investigation of why T cell development generates more CD4 than CD8 lineage T cells.

Ben Seddon C04

T cells develop in1the thymus through a number of well defined developmental stages.
CD4 CD8 double positive thymocytes undergo positive selection which matches TCR restriction to CD4 or CD8 lineage.

Ben Seddon C05

The different developmental stages of thymic selection can be captured by a five compartment mathematical model.
Death within, and transit between compartments can be captured by rate parameters. Equations then use these rates to describe population dynamics with time.

Ben Seddon C06

To help identify model parameters, we take advantage of Zap70-/- mice in which T cell development is arrested. Switching on an antibiotic inducible Zap70 transgene in vivo restores selection.
The kinetics with which different compartments are restored is rich in information that the mathematical model can unlock.

Ben Seddon C07

We identify values for the model parameters that give the best fit (in red) to experimentally observed data (black).

Ben Seddon C08

The model predicts7death rates in the different compartments (top).
Measuring survival of different populations in vivo validates the findings of the model. Survival mirrors the predicted death rates, and reveals an unexpectedly high death rate in DP2 thymocytes.

Ben Seddon C09

Identifying rates of maturation and death provides unique insights into the dynamics of development. Although more CD8 lineage cells start selection, their development is very inefficient, which >80% cells dying at DP2 stage. Fewer CD4 lineage cells die during development. Understanding how apoptosis is regulated in developing thymocytes will be an important 9% question in the future.

Page last modified on 05 feb 15 16:46