Foxp3+ regulatory T (TR) cells limit pathogenic immune responses to self and foreign antigens. An essential role for microRNA (miRNA) in the maintenance and function of TR cells, revealed by the TR-specific Dicer ablation, raised a question as to a specific miRNA contribution. We found that Foxp3 controls the elevated miR155 expression required for maintaining TR proliferative activity and numbers under non-lymphopenic conditions. Moreover, miR155 deficiency in TR cells results in increased SOCS1 expression accompanied by impaired STAT5 activation in response to limiting amounts of IL-2. Our studies suggest Foxp3-dependent regulation of miR155 maintains competitive fitness of TR subset by targeting SOCS1, and provide an experimental support for a proposed role for miRNAs in ensuring the robustness of cellular phenotypes.

Bacterial lipopolysaccharide (LPS) triggers innate immune responses through Toll-like receptor (TLR) 4. We show here that the suppressor of cytokine-signaling-1 (SOCS1/JAB) is rapidly induced by LPS and negatively regulates LPS signaling. SOCS1(+/-) mice or SOCS1(-/-) mice with interferon-gamma (IFNgamma)-deficient background were more sensitive to LPS-induced lethal effects than were wild-type littermates. LPS-induced NO(2)(-) synthesis and TNFalpha production were augmented in SOCS1(-/-) macrophages. Furthermore, LPS tolerance, a protection mechanism against endotoxin shock, was also strikingly reduced in SOCS1(-/-) cells. LPS-induced I-kappaB and p38 phosphorylation was upregulated in SOCS1(-/-) macrophages, and forced expression of SOCS1 suppressed LPS-induced NF-kappaB activation. Thus, SOCS1 directly suppresses TLR4 signaling and modulates innate immunity.

The suppressors of cytokine signaling (SOCS) and cytokine-inducible SH2 protein are key physiological regulators of the immune system. Principally, SOCS1 and SOCS3 regulate T cells as well as antigen-presenting cells, including macrophages and dendritic cells. Here we review the function of SOCS1 and SOCS3 in innate and adaptive immunity, with particular emphasis on the relationship between immune regulation and SOCS.

NetPath, a novel community resource of curated human signaling pathways is presented and its utility demonstrated using immune signaling data.