The immune system maintains health by avoiding the dangers of over-
and under-responses. People with immune systems that do not efficiently
fight off pathogens, like viruses or bacteria, will become sick. On the
other hand, an immune system that is too robust may develop autoimmune
In research published in the prestigious journal Immunity
Saint Louis University researcher reports new findings that help
understand how the immune system's dendritic cells direct other immune
cells called T lymphocytes to continue to learn tolerance for the body's
‘How the immune system's dendritic cells direct other immune cells called T lymphocytes to continue to learn tolerance for the body's own cells has been demonstrated in a new study.’
Daniel Hawiger, associate professor of molecular
microbiology and immunology at SLU, studies a type of immune cell called
dendritic cells which serve as the conductors of the immune system's
"They are the music directors, telling other lymphocytes such as T
cells what to do and how to do it. Their most important role is to
govern immune responses. T cells are the immune system's fighters," Hawiger said. "Dendritic
cells help train T cells to distinguish between self and non-self."
During an infection, dendritic cells direct a battle hymn telling T
cells which entities are pathogens and instructing the T cells to fight
At other moments, they direct a lullaby, instructing T cells not to
fight. Dendritic cells teach self-reactive T cells to leave the body's
own cells and proteins unharmed, creating tolerance toward self.
Usually dendritic cells make the correct decision, playing a rousing call-to-arms or soothing melody, as appropriate.
Sometimes, however, dendritic cells fail to appropriately
down-regulate the immune response. On the other hand, an indiscriminate
tolerance induced by dendritic cells could cause a problem by
unnecessarily dampening the immune response.
While scientists understood the role of dendritic cells, the way in which they accomplish this remained unclear.
Hawiger wanted to learn more about how dendritic cells teach tolerance to T cells.
In research published last year, Hawiger and his team discovered a
previously unknown mechanism that the T cells use to maintain tolerance.
With the current study, they've built on that finding to discover
more about how this T cell mechanism is governed by the functions of
specialized dendritic cells. Specifically, the team reports two key
First, in contrast to what was previously believed, the presentation
of antigens to T cells by all dendritic cells under non-infection,
non-inflammation conditions does not lead to the induction of tolerance.
It also does not lead to immunity. Rather, it causes short term
activation of T cells but no long term effects.
Second, the researchers discovered that tolerance can be induced
only when antigens are acquired and then presented to T cells by a
specialized group of dendritic cells that give specific signals to T
cells. It is only under these special circumstances, using the
mechanisms that Hawiger's team identified, that tolerance occurs.
This improved understanding of how the immune system works offers a
chance to develop new ways to control the body's immune response.
"I hope this new information may help us more precisely regulate the
immune response," Hawiger said. "In the case of an illness like
multiple sclerosis, where the immune response is causing damage, we may
be able to develop a therapy that will dampen that response.
"Perhaps we can harness these functions and learn to turn the volume
up or down, in response to the needs of those with a variety of health
concerns, and in particular, autoimmune diseases."