Biology Reference
In-Depth Information
Within minutes of TCR stimulation, the TCR/CD3 signaling cascade
activates several intracellular enzymes, including calcineurin, which causes
the dephosphorylation of NFAT. This is implicated in the regulation of sev-
eral T-cell activation-associated genes. To monitor both NFAT activation and
T-cell trafficking simultaneously, they constructed a dual bioluminescence
reporter construct where
Gaussia
luciferase was expressed constitutively for
cell trafficking, and click beetle luciferase was linked to NFAT expression.
Transduced stem cells with the construct were used to generate chimeric
mice from which they isolated T-cell progenitors
[82]
. NFAT activation was
first observed 11-14 days after transfer of the T-cell precursors. The localiza-
tion of the NFAT positive T cells was performed by bioluminescence tomog-
raphy (BLT) super-imposed over a subsequently acquired X-ray computed
tomography image set (
Figure 4.1
E). This technology, which can provide
accurate tissue localization and timing of NFAT activation, could provide
new insights into a variety of immunological processes.
Advances in imaging technology
Although optical, nuclear and magnetic resonance imaging technologies
have been used in many small animal imaging studies involving hemato-
poietic stem cell transplantation, there are many new technologies in devel-
opment that will undoubtedly find use in preclinical models and clinics in
the future.
75
Acoustical imaging
Acoustical imaging (ultrasound) works by transmitting high frequency
(1-4 MHz) sound pulses into an animal which are then reflected or
absorbed by internal structures in the body and detected by a probe. It is
a commonly used imaging technology in the clinic as it is inexpensive and
safe. Since most tissues are not very echogenic and have a flat background,
contrast agents (i.e. microbubbles) are needed to differentiate a tissue of
interest from surrounding tissues. Generally ultrasound will detect typi-
cal, non-specific signs of GVHD such as excessive fluid in the bowel lumen,
bowel dilation and bowel wall thickening - features which are also detected
by CT and MRI (reviewed in Schreyer et al.
[117]
). However, by using a
second-generation blood pool contrast medium (SonoVue), which consists
of gas bubbles of non-toxic sulphur-hexafluoride, and color-coded Dop-
pler sonography, it was demonstrated that penetration of microbubbles
within the fluid-filled bowel lumen could be clearly measured in patients
with GVHD, but not in healthy volunteers or patients with chronic bowel
inflammation
[117]
.
Photoacoustic and thermoacoustic imaging
Photoacoustic imaging is a hybrid imaging technology based on the pho-
toacoustic effect. When non-ionizing laser pulses are delivered to tissues,
some of the energy is converted to heat, which causes a rapid thermoelastic
expansion and the generation of an ultrasonic wave. These waves can then
be detected with the same equipment used in ultrasound imaging. Ther-
moacoustic imaging is an extension of photoacoustic imaging, except that
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