Biomedical Engineering Reference
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like receptor 9)
20
expressed in endosomal compartments, they can stimulate
the immune system eficiently. In fact CpG motifs induce B-cell proliferation
and antibody secretion, and they activate APCs to express co-stimulatory
molecules and secrete cytokines, including IL-12 and TNF-
α
.
21,22
. In the
immunostimulatory process by ODN-CpG, the entrance of such DNA sequences
inside the cell and their interaction with endosomal receptors are crucial.
This interaction is usually hampered by the low cellular uptake of ODN-CpGs.
That is why the use of functionalised CNTs has been recently suggested to
increase the ODN-CpG's immunological properties. CNTs bearing positive
charges could represent a valuable tool that can interact with negatively
charged ODN-CpGs. In another study
23
the same research group demonstrated
that it is possible to assess the formation of the supramolecular complexes
between CNTs and DNA through transmission electron microscopy (TEM)
(Fig. 4.6): CNTs were presented in bundles of different diameters, on which
the DNA portion was condensed by forming toroidal clusters, or globular and
supercoiled structures.
For immunisation purposes, a constant amount of ODN-CpGs (0.05 μg/
culture) was initially conjugated to different concentrations of two types of CNTs
Figure 4.6
TEM image of functionalised CNTs (compound
2
): DNA complexes.
Reproduced from Pantarotto
et al.
23
with permission.
Kinetic analyses revealed that the association rate constant (
k
on
) was
higher for compound
4
than for compound
2
. Correspondingly, compound
2
demonstrated a slightly faster dissociation process (
k
off
) compared with
compound
4
. This could be due to the avidity factor of the bivalent ligand
4
.
However, there were no major differences in the binding afinity (
k
d
) of ODN-
CpG motifs to either functionalised
CNTs.
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