Myeloid-derived suppressor cells regulate T cell and B cell responses during autoimmune disease.

MDSCs are a heterogeneous group of myeloid cells that suppress T cell activity in cancer and autoimmune disease. The effect of MDSCs on B cell function is not clear. Using the CIA model of autoimmune disease, we found an increase in M-MDSCs in the periphery of WT mice with CIA compared with naïve mice. These MDSCs were absent from the periphery of CCR2(-/-) mice that developed exacerbated disease. M-MDSCs, isolated from immunized mice, inhibited autologous CD4(+) T cell proliferation. The M-MDSC-mediated suppression of T cell proliferation was NO and IFN-γ dependent but IL-17 independent. Furthermore, we demonstrated for the first time that M-MDSCs from CIA mice also inhibited autologous B cell proliferation and antibody production. The suppression of B cells by M-MDSCs was dependent on the production of NO and PGE2 and required cell-cell contact. Administration of M-MDSCs rescued CCR2(-/-) mice from the exacerbated CIA phenotype and ameliorated disease in WT mice. Furthermore, adoptive transfer of M-MDSCs reduced autoantibody production by CCR2(-/-) and WT mice. In summary, M-MDSCs inhibit T cell and B cell function in CIA and may serve as a therapeutic approach in the treatment of autoimmune arthritis.

Modulation of innate immune signaling by the secreted form of the West Nile virus NS1 glycoprotein.

West Nile virus (WNV) employs several different strategies to escape the innate immune response. We have previously demonstrated that the WNV NS1 protein interferes with signal transduction from Toll-like receptor 3 (TLR3). NS1 is a glycoprotein that can be found intracellularly or associated with the plasma membrane. In addition, NS1 is secreted to high levels during flavivirus infections. We investigated whether the secreted form of NS1 inhibits innate immune signaling pathways in uninfected cells. Secreted NS1 (sNS1) was purified from supernatants of cells engineered to express the protein. Purified sNS1 associated with and repressed TLR3-induced cytokine production by HeLa cells, and inhibited signaling from TLR3 and other TLRs in bone marrow-derived macrophages and dendritic cells. Footpad administration of sNS1 showed the protein associated predominantly with macrophages and dendritic cells in the draining lymph node. Additionally, sNS1 significantly reduced TLR3 signaling and WNV replicon particle-mediated cytokine transcription in popliteal lymph nodes.

Role of myeloid-derived suppressor cells in autoimmune disease.

Myeloid-derived suppressor cells (MDSCs) represent an important class of immunoregulatory cells that can be activated to suppress T cell functions. These MDSCs can inhibit T cell functions through cell surface interactions and the release of soluble mediators. MDSCs accumulate in the inflamed tissues and lymphoid organs of patients with autoimmune diseases. Much of our knowledge of MDSC function has come from studies involving cancer models, however many recent studies have helped to characterize MDSC involvement in autoimmune diseases. MDSCs are a heterogeneous group of immature myeloid cells with a number of different functions for the suppression of T cell responses. However, we have yet to fully understand their contributions to the development and regulation of autoimmune diseases. A number of studies have described beneficial functions of MDSCs during autoimmune diseases, and thus there appears to be a potential role for MDSCs in the treatment of these diseases. Nevertheless, many questions remain as to the activation, differentiation, and inhibitory functions of MDSCs. This review aims to summarize our current knowledge of MDSC subsets and suppressive functions in tissue-specific autoimmune disorders. We also describe the potential of MDSC-based cell therapy for the treatment of autoimmune diseases and note some of hurdles facing the implementation of this therapy.