No abstract

We have generated mice carrying a homozygous null mutation in the granulocyte colony-stimulating factor receptor (G-CSFR) gene. G-CSFR-deficient mice have decreased numbers of phenotypically normal circulating neutrophils. Hematopoietic progenitors are decreased in the bone marrow, and the expansion and terminal differentiation of these progenitors into granulocytes is impaired. Neutrophils isolated from G-CSFR-deficient mice have an increased susceptibility to apoptosis, suggesting that the G-CSFR may also regulate neutrophil survival. These data confirm a role for the G-CSFR as a major regulator of granulopoiesis in vivo and provide evidence that the G-CSFR may regulate granulopoiesis by several mechanisms. However, the data also suggest that G-CSFR-independent mechanisms of granulopoiesis must exist.

Macrophages secrete a variety of proteinases that are thought to participate in remodeling of the extracellular matrix associated with inflammatory processes. We have eliminated expression of the macrophage metalloelastase (MME) gene by targeted disruption to assess the role of this protein in macrophage-mediated proteolysis. We found that the macrophages of MME-deficient (MME -/-) mice have a markedly diminished capacity to degrade extracellular matrix components. In addition, MME -/-macrophages are essentially unable to penetrate reconstituted basement membranes in vitro and in vivo. MME is therefore required for macrophage-mediated extracellular matrix proteolysis and tissue invasion.Macrophages produce a variety of cysteine, serine, and metalloproteinases that are involved with the physiologic tissue remodeling associated with inflammation and wound repair. However, proteolytic activity released by macrophages can also lead to pathologic tissue destruction. Metalloproteinases constitute a family of structurally related matrix-degrading proteinases including the collagenases, stromelysins, gelatinases, matrilysin, membrane-type metalloproteinases, and macrophage metalloelastase. These enzymes require zinc for catalytic activity and are inhibited by the tissue inhibitors of metalloproteinases (1, 2). Macrophage metalloelastase (MME) is characterized by macrophage-specific expression and the capacity to hydrolyze a broad spectrum of substrates (3,4). To determine the contribution of metalloelastase to macrophage-mediated proteolysis, we generated mice deficient in metalloelastase (MME -/-) by targeted mutagenesis. MATERIALS AND METHODSGeneration of the Targeting Construct. A genomic clone encoding MME was isolated from a mouse 129/SvJ library (Stratagene) by using the cDNA as a probe. The

T cell hybridomas require the immediate-early gene NGFI-B (nur77) for T cell receptor (TCR)-mediated apoptosis, a model for negative selection of self-reactive T cells. TCR-mediated death was examined in mice bearing an NGFI-B loss-of-function mutation, either by administration of antibodies to CD3 (anti-CD3) or in two well-characterized transgenic models expressing self-reactive TCRs. Both the extent and the rate of thymocyte death were unimpaired. Anti-CD3-induced death was normal in CD4+ peripheral T cells, in which death is mediated predominantly by the Fas signaling pathway. Thus, no unique requirement for NGFI-B is observed for thymic or peripheral T cell death.