041 – Depletion of myeloid-derived suppressor cells by gemcitabine does not break immune tolerance and protection against EAE induced by mannan-conjugated myelin autoantigens
Anastasia Dagkonaki (1) – Maria Avloniti (1) – Marilena Androutsou (2) – Theodore Tselios (3) – Lesley Probert (1)
Laboratory of Molecular Genetics, Hellenic Pasteur Institute, Athens, Greece (1) – Vianex SA, Athens, Greece (2) – Department of Chemistry, University of Patras, Patras, Greece (3)
Myelin autoantigens conjugated to an oxidized form of the polysaccharide mannan (OM) induce mechanisms that result in antigen-specific peripheral T cell tolerance and strongly protect mice against the development of EAE when administered with prophylactic and therapeutic protocols. Mannan-conjugated peptides activate innate and adaptive immune systems, but the mechanism of tolerance is not yet known. Protection is antigen-specific showing T cell specificity but is not associated with described mechanisms of T cell tolerance apart from some features of anergy. Mannan targets the mannose receptor which is present on myeloid lineage cells, and mannan-conjugated peptides induce maturation of in vitro differentiated mouse dendritic cells. In this study we investigated the possibility that mannan peptides induce the expansion of myeloid-derived suppressor cells (MDSC), a heterogenous population of myeloid cells characterized by their immature state and their ability to suppress immune responses, possibly in an antigen-specific manner. Groups of female C57BL/6 mice were injected i.d. with soluble OM-MOG (37 _g MOG equivalent), or vehicle, prior to immunization with MOG/adjuvant for T cell priming or the induction of EAE, and splenocytes were analyzed for MDSC expansion by FACS. Immunization with MOG/adjuvant induced the expansion of Cd11b-gated Ly6C+Ly6G-(monocyte MDSC) and Ly6CintLy6G+ (granulocyte MDSC) cells equally in the spleens of OM-MOG and vehicle-vaccinated mice. Interestingly, OM-MOG vaccinated mice showed equal proportions of both splenic MDSC cell types as vehicle-injected and nave mice, suggesting that OM-MOG is not sufficient to induce MDSC expansion. We next investigated the effects of MDSC depletion on the development of EAE in OM-MOG injected mice. Gemcitabine is a cytotoxic drug that targets MDSC, and gemcitabine administration (60 mg/Kg ip, days 14,16,18,20,22,24 post-immunization for induction of MOG-EAE) in mice OM-MOG-tolerized mice efficiently depleted monocytic, and to a lesser extent granulocytic MDSC, in peripheral blood during the development of EAE. However, gemcitabine administration did not significantly alter the protective effects of OM-MOG on the clinical symptoms of EAE suggesting that MDSC do not play a major role in immune tolerance induced by mannan peptides.