The role of suppressor of cytokine signaling 1 as a negative regulator for aberrant expansion of CD8α⁺ dendritic cell subset

The suppressor of cytokine signaling (SOCS) 1 is a negative regulator in multiple cytokine-related aspects to maintain immunological homeostasis. Here, we studied a role of SOCS1 on dendritic cell (DC) maturation in the mice lacking either TCRα chain or CD28 in SOCS1-deficient background, and found that the SOCS1 could restore acute phase of inflammatory response in SOCS1-deficient mice. The CD11c⁺ CD8^- DC population in freshly isolated splenic DCs from normal mice highly expressed SOCS1. However, in SOCS1-deficient environment, the proportion of CD8α⁺ DCs (CD8 DCs) noticeably increased without affecting the cell number of conventional and plasmacytoid DC populations. This population revealed the CD11c^dull CD8α⁺ CD11b^- CD45RA^- B220^- phenotype, which is a minor population in normal mice. Localization of the abnormal CD8 DCs in splenic microenvironments was mainly restricted to deep within red pulp. The CD8 DCs secrete a large amount of IFN-γ, IL-12 and B lymphocyte stimulator/B cell activation factor of the tumor necrosis factor family in response to LPS and CpG stimulation. This is responsible for the development of DC-mediated systemic autoimmunity in the old age of SOCS1-deficient mice. Moreover, the CD8 DC subsets expressed more indoleamine 2,3-dioxygenase and IL-10, and hence inhibit the allogeneic proliferative T cell response and antigen-induced T_h1 responses. Therefore, SOCS1 expression during DC maturation plays a role in surveillance in controlling the aberrant expansion of abnormal DC subset to maintain homeostasis of immune system.