Biomedical Engineering Reference
In-Depth Information
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Figure
8.5
The complex composition dependence (CpG; 0.5 mM) of IL-12
production from the thio-Mws after incubation for 24 h (n 5 3); N.D.
5 not detectable.
[dA] 5 2. At [mG]/[dA] 5 5, the complex induced about seven-fold
(5.2 ng mL
21
) higher production than that of naked CpG-dA60, and the
production decreased with further increase of the amount of SPG.
Interestingly, between [mG]/[dA] 5 1 and 5 there was a significant difference
in the IL-12 production from cells, while the amount of CpG-dA60 taken up
by the cells differed only slightly among them (data not shown). In addition,
this drastic increase did not occur when the mixture of CpG-dA60 and SPG,
but not the complex, was treated. When multiple CpG DNAs are conjugated
on one substrate and this substrate is taken up by macrophages, the cytokine
production is dramatically (or allosterically) induced.
50-53
This is explained by
the observation that the multiple DNAs increase local concentrations of CpG
sequences in endolysosomes and, subsequently, TLR9 recognition of CpG
DNA and further signals are enhanced. The allostericity is probably related to
the fact that dimerization of TLR9 is necessary for its activation.
54
In addition,
our recent study has shown that the flexibility of the polymer containing CpG
DNA is a key to induce the large amount of IL-12.
55
Once one CpG branch
binds to one TLR9 dimer, the polymer is locked adjacently to the vesicle
surface where other TLR9 dimers are present. When the structure is flexible
enough to turn, the second binding can easily occur, and the adjacent second
binding seems to be critical for the allosteric effect. At [mG]/[dA] , 2in
Figure 8.5, the complex is considered to have the maximum number of CpG-
dA
60
due to the DNA-rich composition. On the other hand, at [mG]/[dA] . 2,
most of the complexes have fewer CpG-dA
60
than at [mG]/[dA] , 2 due to the
SPG-rich composition. With increasing [mG]/[dA], the flexibility of the
complex is considered to increase. The complex with a rigid structure could
only access the adjacent TLR9 dimers with difficulty, while the complex with a
flexible structure could access them easily. Therefore, the cytokine secretion
drastically increased at [mG]/[dA] . 2 because of the easy accessibility of the
