Prevention and treatment of experimental autoimmune encephalomyelitis by soluble CD83.

CD83 is up-regulated on the surface of dendritic cells (DCs) during maturation and has been widely used as a marker for mature DCs. Recently, we reported the recombinant expression of the extracellular immunoglobulin domain of human CD83 (hCD83ext). Using this soluble form of CD83, allogeneic as well as specific cytotoxic T lymphocyte proliferation could be blocked in vitro. Here we report the functional analysis of soluble CD83 in vivo, using murine experimental autoimmune encephalomyelitis (EAE) as a model. Strikingly, only three injections of soluble CD83 prevented the paralysis associated with EAE almost completely. In addition, even when the EAE was induced a second time, CD83-treated mice were protected, indicating a long-lasting suppressive effect. Furthermore, soluble CD83 strongly reduced the paralysis in different therapeutic settings. Most important, even when the treatment was delayed until the disease symptoms were fully established, soluble CD83 clearly reduced the paralyses. In addition, also when EAE was induced a second time, soluble CD83-treated animals showed reduced disease symptoms. Finally, hCD83ext treatment almost completely reduced leukocyte infiltration in the brain and in the spinal cord. In summary, this work strongly supports an immunosuppressive role of soluble CD83, thereby indicating its therapeutic potential in the regulation of immune disorders in vivo.

Determination of the inhibitory activity and biological half-live of soluble CD83: comparison of wild type and mutant isoforms.

A soluble form of CD83 ("sCD83") has been shown to block DC-mediated T cell stimulation in vitro and an immunosuppressive role has also been shown in vivo using an experimental-autoimmune-encephalomyelits (EAE) model. Using recombinant mutational analyses, recently, we could show that sCD83 forms a homo-dimer, whereby four cysteines are involved in the intra-molecular disulfide bonds and the fifth cysteine is responsible for the inter-molecular bridging of the two molecules. Further studies revealed that the two CD83-isoforms, i.e. the dimer and the monomer, have a similar inhibitory capacity when tested in vitro. Here we show that the biological (in vivo) half-life of the two sCD83 isoforms is comparable and was between 2 and 3h. In addition, using the EAE-model, we were able to show that a monomeric-mutant isoform of soluble CD83 has a similar inhibitory activity in vivo when compared with a dimeric-wildtype isoform.

Cloning and characterization of the promoter region of the human CD83 gene.

Human CD83 (hCD83) is a glycoprotein expressed predominantly on the surface of dendritic cells (DC). To get insight into the regulation of hCD83 expression, we cloned a 3037 bp fragment up-stream of the translation initiation codon. Deletion mutants were constructed revealing highest promoter activity in the -261 fragment containing four SP1 binding sites and one NF-kappaB element. Electrophoretic mobility shift assays demonstrated the specific interaction of NF-kappaB factors with the NF-kappaB element as well as specific binding of SP1 and SP3 to the SP1 binding site. The hCD83 promoter was inducible by TNF-alpha. This inducibility was strictly dependent on the intact NF-kappaB element.

Role of CD83 in the immunomodulation of dendritic cells.

Glycoprotein CD83 is one of the best-known maturation markers for human dendritic cells (DCs). The fact that CD83 is strongly upregulated together with co-stimulatory molecules such as CD80 and CD86 during DC maturation suggests it plays an important role in the induction of immune responses. Infection studies with herpes simplex virus type 1 (HSV-1) and the inhibition of the CD83 mRNA specific transport from the nucleus to the cytoplasm suggested a possible functional role for CD83. The first clear proof that CD83 is indeed important for DC biology came from recently performed studies using a soluble form of the extracellular CD83 domain. DC-mediated T cell proliferation could be completely inhibited using this recombinant molecule. Additional studies elucidated immunostimulatory as well as regulatory effects of the CD83 molecule. Furthermore, CD83-/- knockout mice revealed a block in CD4+ T cell generation, a new possible immunomodulatory function of CD83.