Hematopoietic stem cells rarely contribute to hepatic regeneration, however, the mechanisms governing their homing to the liver, which is a crucial first step, are poorly understood. The chemokine stromal cell-derived factor-1 (SDF-1), which attracts human and murine progenitors, is expressed by liver bile duct epithelium. Neutralization of the SDF-1 receptor CXCR4 abolished homing and engraftment of the murine liver by human CD34 + hematopoietic progenitors, while local injection of human SDF-1 increased their homing. Engrafted human cells were localized in clusters surrounding the bile ducts, in close proximity to SDF-1-expressing epithelial cells, and differentiated into albumin-producing cells. Irradiation or inflammation increased SDF-1 levels and hepatic injury induced MMP-9 activity, leading to both increased CXCR4 expression and SDF-1-mediated recruitment of hematopoietic progenitors to the liver. Unexpectedly, HGF, which is increased following liver injury, promoted protrusion formation, CXCR4 upregulation, and SDF-1-mediated directional migration by human CD34 + progenitors, and synergized with stem cell factor. Thus, stress-induced signals, such as increased expression of SDF-1, MMP-9, and HGF, recruit human CD34 + progenitors with hematopoietic and/or hepatic-like potential to the liver of NOD/SCID mice. Our results suggest the potential of hematopoietic CD34 + /CXCR4 + cells to respond to stress signals from nonhematopoietic injured organs as an important mechanism for tissue targeting and repair.

Hematopoietic stem cells rarely contribute to hepatic regeneration, however, the mechanisms governing their homing to the liver, which is a crucial first step, are poorly understood. The chemokine stromal cell–derived factor-1 (SDF-1), which attracts human and murine progenitors, is expressed by liver bile duct epithelium. Neutralization of the SDF-1 receptor CXCR4 abolished homing and engraftment of the murine liver by human CD34+ hematopoietic progenitors, while local injection of human SDF-1 increased their homing. Engrafted human cells were localized in clusters surrounding the bile ducts, in close proximity to SDF-1–expressing epithelial cells, and differentiated into albumin-producing cells. Irradiation or inflammation increased SDF-1 levels and hepatic injury induced MMP-9 activity, leading to both increased CXCR4 expression and SDF-1–mediated recruitment of hematopoietic progenitors to the liver. Unexpectedly, HGF, which is increased following liver injury, promoted protrusion formation, CXCR4 upregulation, and SDF-1–mediated directional migration by human CD34+ progenitors, and synergized with stem cell factor. Thus, stress-induced signals, such as increased expression of SDF-1, MMP-9, and HGF, recruit human CD34+ progenitors with hematopoietic and/or hepatic-like potential to the liver of NOD/SCID mice. Our results suggest the potential of hematopoietic CD34+/CXCR4+cells to respond to stress signals from nonhematopoietic injured organs as an important mechanism for tissue targeting and repair

Induced human fibroblasts produce several mRNAs encoding interferon (IFN) activity. We previously cloned cDNA for a 1.3‐kb RNA designated IFN‐beta 2 and distinct from the 0.9‐kb IFN‐beta 1 mRNA. In vitro transcription‐‐translation mapping of the full‐length IFN‐beta 2 cDNA sequence, shows that it encodes a 23.7‐kd protein of 212 amino acids. This cDNA, fused to the SV40 early gene promoter, was transfected and amplified in Chinese hamster ovary cells and clones were obtained which constitutively produce human interferon activity. Two IFN‐beta 2 genomic clones were isolated and their expression in hamster and mouse cells also produces biologically active rIFN‐beta 2. Specific immunoassays show that IFN‐beta 2 secreted by DNA‐transformed rodent cells is a processed 21‐kd protein, whose activity is cross‐neutralized by antibodies to human IFN‐beta 1 but not to IFN‐alpha or gamma. The immunoassay also demonstrates the induction of IFN‐beta 2 secretion by fibroblasts in response to growth‐regulatory cytokines, such as interleukin‐1 and tumor necrosis factor. The function of this IFN‐beta 2 as an autoregulatory inhibitor of cell growth is discussed.

A set of five clinical characteristics can be used in randomized studies to select lower back pain that will be well relieved by facet joint anesthesia. These characteristics should not, however, be considered as definite diagnostic criteria of lower back pain originating from facet joints.

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