Attached
Introductions
Dengue viral infection in humans can manifest as asymptomatic or symptomatic infection, with a wide spectrum of
clinical manifestations ranging from undifferentiated fever to life threatening illness. The majority of the dengue
infections in humans are asymptomatic. Cells infected by dengue virus (DENV) are known to produce cytokines _nd other soluble mediators and increases in these factors are considered to contribute to disease pathogenesis.
These different cytokines have been shown to have associations with different degrees of disease severity in acute
DENV infections. One of the main cell types infected by DENV are monocytes, and virus infection induces the
production of various anti-viral, pro-inflammatory and anti-inflammatory cytokines from monocytes.
Methods
Twelve healthy individuals with two past dengue infections with which resulted in either asymptomatic infection or
dengue hemorrhagic fever (DHF) were recruited (6 people in each group). Monocytes were isolated with CD14
beads using MACS separating columns. Monocytes were then infected at a multiplicity of infection of one with
DENV serotype 2 (DENV-2) and DENV serotype 3 (DENV-3) and incubated for 24 hours. Culture supernatant was
assayed for levels of IFN- , IFN-~, TNF-, IL-l0, IL-8, IL-6, IL-12p70, IL-17 and IP-l 0 with luminex assays.
Results
As expected, monocytes from those who had past asymptomatic group produced significantly more IFN- when
infected with DENV-2 and DENV-3, compared to uninfected monocytes (DENV-2; p<O.OOO1, DENV-3; P=O.OOOl).
However, monocytes of those who had past DHF failed to produce significant levels of IFN when infected with
either DENV-2 or DENV-3 (DENV-2; p=0.2988, DENV-3; P=0.4435). Further monocytes from those with past DHF
spontaneously produced more than twice the amount of TNF- (p=O.Ol) and three times the amount of IL-8
"p<O.OOOl) compared to monocytes of those who had past asymptomatic infection. In addition, monocytes of those
with past DHF produced significantly more TNF (DENV-2, p=0.002; DENV-3: p=0.02) and IL-8 (DENV-2:
p=0.008; DENV-3: p=0.002) when infected with DENV-2 and DENV-3. Significant amounts of IP-l0 were
produced by DENV-2 and DENV-3 infected monocytes of individuals with both past asymptomatic infection and
those with past DHF. Production of IL-l0, IL-12p70 and IL-6 from infected monocytes was not significantly different
between asymptomatic and DHF groups. Neither uninfected nor infected monocytes produced IFN-~ in both
asymptomatic and symptomatic groups.
Conclusion
Failure to produce a significant amount of IFN- in response to the DENV by monocytes of those with past DHF, is
suggestive that they could be having impaired antiviral responses to the virus. In addition, since monocytes of those
with past DHF also spontaneously produced significantly higher levels of TNF and IL-8, an altered immune
response generated by their monocytes could contribute to severe clinical disease
