NanoSight, world-leading manufacturers of unique
nanoparticle characterization technology reports that the School of Medicine at
the University of St Andrews is using nanoparticle tracking analysis, NTA, to
characterize exosome behaviour.
Dr Simon Powis and his colleagues at the University of St Andrews are working
to understand how a set of molecules involved in the immune system's defence
against intracellular pathogens function. These molecules are called major
histocompatibility complex (MHC) class I molecules, and they are expressed on
almost every cell in the body. Their relevance to medicine is most commonly
known because they are one of the key sets of genes that have to be closely
matched when an organ transplant is made, otherwise the transplant can be
rejected. It is now known that their precise role in the normal immune system
is to bind small fragments of degraded viral proteins which they display to T
lymphocytes of the immune system. This allows the specific detection of
'foreign' proteins, i.e. from potential pathogens, and allows the immune system
to specifically detect and kill infected cells, whilst leaving a neighbouring
uninfected cell alone. In addition, there is one fascinating autoimmune disease
closely associated with a particular type of MHC class I molecule. Over 90% of
patients with a type of inflammatory arthritis called ankylosing spondylitis
which affects the spine, expresses one specific type of MHC class I molecule
called HLA-B27. The link between this arthritic condition and HLA-B27 has been
known for almost 40 years, but the disease mechanism and how HLA-B27 is
involved is yet to be understood.
Whilst the Powis group were studying MHC class I molecules expressed on
exosomes, it was discovered that they can express a novel type of structure.
The tail region of the MHC class I molecule, which sits inside the exosome, can
frequently form a disulfide-bond linkage to another MHC class I molecule, thus
bringing two molecules closely together in a dimeric structure. This normally does
not happen on cells because the cytoplasm has a reducing environment,
preventing disulfide bonds from forming. However, in exosomes the capacity to
maintain a reducing environment seems to have been lost. The group is now
studying whether cells of the immune system see these MHC class I dimers
structures on exosomes and respond to them. Another key question is what
peptides are found bound to MHC class I molecules on exosomes. The exosome
production pathway is not the normal route for MHC class I molecules to get to
the cell surface, so the possibility that different peptides are found in this
subset of exosomal MHC class I molecules is a real possibility. To be able to
study these exosomes from a variety of immune cells, it is necessary to detect
their presence and size in cultures. This is the reason for the team choosing
the NanoSight NTA approach with the LM10 system.
Prior to using NanoSight, flow cytometry had proved a valuable tool in the
preliminary characterisation of the exosomes released by immune cells. Dr Powis
says "The NanoSight approach allows a more accurate determination of size and
relative concentration both before and after purification. This allows us to
monitor the release of exosomes in the range 30-150nm after activation with a
variety of immune stimuli relevant to both normal and aberrant immune responses
in a way not previously visible with flow cytometry."
To learn more about nanoparticle characterization using Nanoparticle Tracking
Analysis, NTA, please visit the
company website (
www.nanosight.com)
and register for the latest issue of NanoTrail, the company's electronic
newsletter.
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