Background: Activation of vascular endothelial cells (EC), as occurring for
example in organ transplantation, is characterized by shedding of heparan
sulfate (HS), which is an important regulator of intravascular coagulation
and inflammation. Soluble HS is known to activate dendritic cells (DC) via
Toll-like receptor 4 (TLR).
Hypothesis: Low molecular weight dextran sulfate (DXS, MW 5000) has
been reported to inhibit all three complement pathways as well as the
coagulation cascade. Furthermore, in vitro and in vivo work has shown,
that DXS acts as an EC protectant inhibiting complement-mediated
endothelial damage. We therefore hypothesized that DXS might be able to
interfere with antigen presentation by blocking DC maturation, and that
this effect may facilitate induction of immunological tolerance.
Methods and Results: Human DC were propagated from monocytes with
GM-CSF and IL-4 for 6 days. Immature DC were stimulated with different
exogenous (e.g. LPS or LAM) and endogenous ligands (e.g. HS) of TLR to
induce maturation. As shown by FACS analysis, addition of DXS during
promoted DC maturation was able to dose-dependently prevent upregulation
of molecules such as CD40, CD83, CD80/CD86 as well as ICAM-1. In the
case of CD86 for example, maturation induced by HS was totally inhibited
with 5 mg/ml DXS (MFI ± SD; 61.3 ± 7.2 mature DC versus 8.2 ± 1.5 for
DXS with 5 mg/ml; p<0.001; n=4). To exclude that the effect of HS was due
to a contamination with LPS, HS was pretreated with Limulus anti LPSfactor
coated silica beads. Mature DC function was examined by the ability
of the cells to stimulate autologous T cells. Treatment with DXS significantly
inhibits DC-mediated T cell proliferation. Binding of DXS to DC was
investigated using fluorescein labeled DXS. Furthermore, DXS does not
seem to influence differentiation of monocytes into immature DC analyzed
by the expression of the surface markers CD14 and CD1a.
Conclusions and Outlook: We have demonstrated that DXS is able to
prevent phenotypic and functional maturation of DC, which is necessary
to interact with T cells and generate acquired immune responses. DXS and
similar substances, which prevent maturation of DC, may thus be useful in
the field of organ transplantation. Follow-up experiments will investigate
if alterations of DXS treated DC are associated with a reduced nuclear
translocation of NF-kappaB.