Immunosuppressive Drugs up-Regulate the Immunoinhibitory Receptor Osteoactivin On Human Monocyte-Derived Dendritic Cells

Dendritic cells (DC) abundantly express the type I transmembrane glycoprotein Osteoactivin (OA) - also known as transmembrane glycoprotein NMB and DC-HIL - compared to low expression levels on monocytes. Antigen-presenting cells interact via OA with the type I transmembrane proteoglycan syndecan-4 (SD-4) on T cells which inhibits T cell activation. We previously reported on increased expression of OA upon exposure of monocyte-derived DC (moDC) to immunosuppressive drugs (e.g., Gutknecht et al ASH annual meeting 2011). Here we extended these analyses and comparatively analyzed the impact of various immunsuppressive drugs (ID) on moDC phenotype and function.

The moDC were generated from blood monocytes by plastic adherence and exposure to GM-CSF and IL-4. Clinically relevant concentrations of ID were added to the culture medium every second day starting with the first day of culture (cyclosporine A: 1μg/ml, prednisolone: 3.5μg/ml, tacrolimus: 10ng/ml, mycophenolat-mofetil 0.1μM, methotrexat 230ng/ml). Cells were harvested for immunophenotyping by flow cytometry, western-blotting and real-time PCR. Cytokine release by moDC was determined on day 7 by ELISA. Functional properties were determined by mixed lymphocyte reactions (MLR) on day 7 of culture.

Exposure of moDC to therapeutic concentrations of prednisolone resulted in significantly reduced expression of the costimulatory molecules CD83 and CD86 and increased levels of the monocyte marker CD14, indicative of impaired differentiation. Tacrolimus significantly increased CD14 expression and reduced CD83 expression, while the other ID did not cause significant alterations. All ID altered the release of the immunomodulatory cytokines IL-10, IL-6 and TGF-ß. Notably, all ID except cyclosporine A caused a substantial upregulation of the immunoinhibitory receptor OA in moDC. The extent of OA expression increased over time of exposure to ID during differentiation and resulted in reduced capacity of the moDC to stimulate allogenic T cells which could be restored by disruption of OA/SD-4 interaction using a blocking OA antibody.

Increased expression of OA on moDC upon exposure to ID contributes to inhibition of T-cell activation. The mechanisms underlying the differential effect of cyclosporine A are presently under study. Our results indicate that targeting OA/SD-4 interaction may hold promise for modulation of T cell responses in various pathophysiological conditions and immunotherapeutic strategies.

No relevant conflicts of interest to declare.