increase the avidity by circulating DENV with a consequent
increase in the rate of infection. This result was similar to
that found by Plazolles et al.,
21
who demonstrated increased
CMV infection in the presence of recombinant sDC-SIGN.
When they performed CMV infection testing on monocyte-
derived Dendritic Cells (moDC) with MOI = 1, for 24 to 48 h in
the presence of decreasing amounts of soluble isoforms 6
(sDC-SIGN1A type I) and 8 (sDC-SIGN1A type III) (400 to
12.5 ng/mL), they observed about double the infected DCs
than in infection control, with a concentration between
100 ng/mL and 50 ng/mL of protein. Concentrations greater
than 100 ng/mL and less than 50 ng/mL of the sDC-SIGN1A
type I recombinant isoform 6 showed no difference in infec-
tion rate.
Other studies have shown blockade of
S. aureus
and HIV
infection in the presence of soluble DC-SIGN isoforms. Kwon
et al.
19
and Navarro-Sanchez et al.
35
suggested DC-SIGN pro-
tein increases viral HIV and DENV infection only when
expressed in the cell membrane. In both studies, there was
blockade of infection by sDC-SIGN with MOI variable from 5
to 10; however, only CRD was produced and considered as sol-
uble DC-SIGN. Kwon et al. further demonstrated that mDC-
SIGN with the truncated cytoplasmic domain region is capa-
ble of capturing circulating viruses but is unable to internalize
them with low MOI.
19
This corroborates the highlighted
importance in our study that isoforms be fully studied, as
they exist
in vivo
, because all portions of the protein perform
functions that are still being discovered.
Another possible justi
fi
cation for the results found in the
present work is that at high concentration (100 ng/mL) there
is bioavailability of sDC-SIGN that complexes rapidly but
inef
fi
ciently to circulating viral particles acting as opsonins
rather than infection blockers. Thus, soluble isoforms at
high concentrations could lead to a high number of immobi-
lized viral particles to capture and internalize by iDCs, favor-
ingfavouring infection. As already described by Mikloska et
al.,
36
this hypothesis presents th
e need for another receptor
that favors iDC opsonization, such as CD11b has been shown
to facilitate HIV opsonization by iDC mDC-SIGN-depen-
dence. It is also possible that these aggregates (virus + sDC-
SIGN) may associate with mDC-SIGN and somehow facilitate
viral penetration into cells. These data indicate that the
virus
‘
opsonized
’
by sDC-SIGN is more effectively captured
by iDCs than free viruses. sDC-SIGN molecules capable of
interacting with infectious agents at high serum concentra-
tions could potentiate the severity of diseases such as Den-
gue, since infection itself can alter the expression pattern of
isoforms.
21
,
36
DC-SIGN molecules in tetramers are known to bind to
better af
fi
nity N-glycan residues, with the neck region of the
protein essential in this oligomerization.
3
,
14
Although iso-
form 8 has unchanged CRD, its neck region is altered and it
is well demonstrated that it is through this region that inter-
action with other soluble and membrane isoforms occurs.
14
Even so, in our results a signi
fi
cant increase in infection was
also found in the trials with the presence of this isoform
(
Table 1
). One possible explanation for this is that remaining
amino acid residues in the neck region of isoform 8 (three
and a half tandem repeats) are suf
fi
cient to promote interac-
tion with other neck regions of membrane isoforms also
forming the multimers responsible for the increase of avid-
ity for DENV-2 and, consequently, increasing the infection
rate. Moreover, because it is a smaller molecule than the
complete isoform, isoform 8 linked to DENV could be more
easily internalized.
The second hypothesis was that recombinant soluble iso-
forms capable of binding to DENV could interact with each
other to form stable multimers that could neutralize circulat-
ing viral particles and, consequently, the binding, internaliza-
tion, and infection of iDCs. This hypothesis was discarded in
experiments with isoforms 8 and 10 at 100 ng/mL.
Besides the possibility of observing this process
in vitro
assays, these events could also occur with circulating sDC-
SIGN, naturally or via therapeutic administration, neutraliz-
ing the infection, and therefore, it is important to observe the
necessary concentrations of circulating isoforms to provide
blockade. Schmid and Harris
37
proposed that the skin is an
important site for therapeutic actions or even for intradermal
vaccination, since DCs and macrophages are the primary tar-
get of DENV infection with additional monocyte recruitment
for further differentiation into iDCs susceptible to infection
and subsequent antigen presentation.
DENV causes a diverse spectrum of disease ranging from
asymptomatic infection and mild febrile illness to more seri-
ous complications, including hemorrhage and shock. The
associations between host genetics, DENV infection and clini-
cal outcome are complex and may involve more than one fac-
tor such as age, ethnicity, primary or secondary infection,
patient
’
s metabolic conditions and even genetic factors that
lead to the expression of proteins involved in the process. of
infection.
38
,
39
Studies demonstrate the relationship between the severity
of the disease and the different polymorphism pro
fi
les of
genes that express proteins associated with DENV infection,
such as DC-SIGN.
40
,
41
This demonstrates the importance of
the protein structure of receptors for viral infection. There-
fore, therapeutic strategies targeting protein structures
involved in the DENV infection process, associated with a
higher degree of infection, as observed in the present study
for DC-SIGN isoforms 8 and 10, are promising.
Infection experiments in the presence of soluble isoform
12 presented different results from other isoforms. This iso-
form does not appear to interact with circulating viral par-
ticles at any concentration, neither increasing nor decreasing
the infection rate compared to the infection control. The
results obtained were statistically similar to those found in
viral control. This result is in agreement with those found in
the mannose column binding experiments which demon-
strated the inability of this soluble isoform to bind to these
residues.
23
Thus, isoform 12 would be unable to bind to DENV
glycoprotein E, apparently not interfering in any way with the
infection process.
Unlike isoforms 8 and 10, isoform 12 has an altered CRD
region, which is essential for the binding and internalization
of DENV in the cell.
9
Therefore, it can be inferred that the
absence of this region prevents the interaction of the virus
with isoform 12, maintaining infection levels similar to those
of the viral control.
Finally, an important aspect to be analysed in new stud-
ies is the relationship between viral infection and variation
braz j infect dis.
2024;
28(6)
:103873
7