The suppressor of cytokine signaling (SOCS) family of negative regulatory proteins is up-regulated in response to several cytokines and pathogen-associated molecular patterns (PAMP) and suppresses cellular signaling responses by binding receptor phosphotyrosine residues. Exposure of bone marrow-derived dendritic cells (BMDC) to 1D8 cells, a murine model of ovarian carcinoma, suppresses their ability to express CD40 and stimulate antigen-specific responses in response to PAMPs and, in particular, to polyinosinic acid:poly-CMP (polyI:C) with the up-regulated SOCS3 transcript and protein levels. The ectopic expression of SOCS3 in both the macrophage cell line RAW264.7 and BMDCs decreased signaling in response to both polyI:C and IFNalpha. Further, knockdown of SOCS3 transcripts significantly enhanced the responses of RAW264.7 and BMDCs to both polyI:C and IFNalpha. Immunoprecipitation and pull-down studies show that SOCS3 binds to the IFNalpha receptor tyrosine kinase 2 (TYK2). Because polyI:C triggers autocrine IFNalpha signaling, binding of SOCS3 to TYK2 may thereby suppress the activation of BMDCs by polyI:C and IFNalpha. Thus, elevated levels of SOCS3 in tumor-associated DCs may potentially resist the signals induced by Toll-like receptor 3 ligands and type I IFN to decrease DC activation via binding with IFNalpha receptor TYK2.