TNF-? is a pleiotropic cytokine involved in the regulation of various biological effects, including cell survival and proliferation, cell differentiation, and cell death. Moreover, TNF-? triggers proinflammatory responses, essentially through its ability to promote the expression of various proinflammatory genes. Most of the biological effects initiated by TNF-? rely on its ability to bind to and activate TNF-R1. As a consequence, molecular complexes are being formed, resulting from the recruitment of multiple adaptor proteins to the intracellular TNF-R1 DD. The adaptor protein FAN constitutively binds to a proximal membrane domain of TNF-R1 called NSD. Herein, the role of FAN in TNF-?-induced cell signaling and biological responses is discussed.
Factor associated with neutral sphingomyelinase activation (FAN) is an adaptor protein that constitutively binds to TNF-R1. Microarray analysis was performed in fibroblasts derived from wild-type or FAN knockout mouse embryos to evaluate the role of FAN in TNF-induced gene expression. Approximately 70% of TNF-induced genes exhibited lower expression levels in FAN-deficient than in wild-type fibroblasts. Of particular interest, TNF-induced expression of cytokines/chemokines, such as IL-6 and CXCL-2, was impaired in FAN-deficient cells. This was confirmed by real time RT-PCR and ELISA. Upon i.p. TNF or thioglycollate injection, neutrophil recruitment into the peritoneal cavity was reduced by more than 50% in FAN-deficient mice. Nevertheless, FAN-deficient animals did not exhibit an increased susceptibility to different microorganisms including bacteria and parasites, indicating that FAN is not essential for pathogen clearance. Specific Ab response to BSA was substantially impaired in FAN-deficient mice and this was associated with a reduced content of leukocytes in the spleen of BSA-challenged FAN-deficient mice as compared with their wild-type counterparts. Altogether, our results indicate the involvement of FAN in TNF-induced gene expression and leukocyte recruitment, contributing to the establishment of the specific immune response.
B regulatory cells are a newly described subpopulation of B cells that appear to play important roles in autoimmunity and more recently, in cancer. In this review we summarize our current knowledge of B regulatory cells, as well as the body of evidence pointing towards a role for B cells in general, and B regulatory cells in particular, in promoting tumor growth.
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