Melinda A. Borrello

Fibroblast heterogeneity in the healing wound

Although fibroblasts are traditionally described as static cells providing framework and support for tissues, there is an accumulating body of evidence showing that fibroblasts are a dynamic cell type which exist in functionally and morphologically heterogeneous subpopulations. Fibroblast subsets have been shown to play a critical role in the production and regulation of extracellular matrix components, in wound repair and regeneration, and have been implicated in the pathogenesis of fibrotic conditions. We have reviewed the evidence supporting heterogeneity of fibroblasts from pulmonary, periodontal, and dermal tissues. In addition, we will explore the role fibroblast subpopulations may play in the complex process of wound repair and regeneration.

Biphenotypic B / macrophage cells express COX‐1 and up‐regulate COX‐2 expression and prostaglandin E2 production in response to pro‐inflammatory signals

B / macrophage cells are biphenotypic leukocytes of unknown function that simultaneously express B lymphocyte (IgM, IgD, B220, CD5) and macrophage (phagocytosis, F4 / 80, Mac‐1) characteristics. B / macrophage cells can be generated from purified mouse B lymphocytes incubated in fibroblast‐conditioned medium. A potential role for B / macrophage cells in inflammation was shown by their ability to express prostaglandin H synthase‐1 (COX‐1) and prostaglandin H synthase‐2 (COX‐2) and by their production of prostaglandin (PG) E2. COX‐1 and COX‐2 mRNA expression is not observed in the precursor B lymphocytes and is not known to be a property of B lineage cells. In contrast, COX‐2 and the prostanoids PGE2, PGF2α and PGD2 are highly inducible in B / macrophage cells upon stimulation with lipopolysaccharide, CD40 ligand, or via engagement of surface IgM, supporting a role for these cells in inflammation. PGD2 and its metabolites are of interest because they activate the nuclear receptor PPARγ that regulates lipid metabolism. The B / macrophage represents the first instance of a normal B‐lineage cell capable of expressing COX‐2. Importantly, B / macrophage cells were identified in vivo, providing evidence that they may play a significant role in immune responses. Since PGE2 blunts IL‐12 production, its synthesis by B / macrophage cells may shift the balance of an immune response towards Th2 and humoral immunity.

C35 (C17orf37) is a novel tumor biomarker abundantly expressed in breast cancer

Identification of shared tumor-specific targets is useful in developing broadly applicable therapies. In a study designed to identify genes up-regulated in breast cancer, a cDNA clone corresponding to a novel gene C35 (C17orf37) was selected by representational difference analysis of tumor and normal human mammary cell lines. Abundant expression of C35 transcript in tumors was confirmed by Northern blot and real-time PCR. The C35 gene is located on chromosome 17q12, 505 nucleotides from the 3′ end of the ERBB2 oncogene, the antigenic target for trastuzumab (HerceptinTM) therapy. The chromosomal arrangement of the genes encoding C35 and ERBB2 is tail to tail. An open reading frame encodes a 12-kDa protein of unknown function. Immunohistochemical analysis detected robust and frequent expression of C35 protein, including 32% of grade 1 and 66% of grades 2 and 3 infiltrating ductal carcinomas of the breast (in contrast to 20% overexpressing HER-2/neu), 38% of infiltrating lobular carcinoma (typically HER-2/neu negative), as well as tumors arising in other tissues. C35 was not detected in 38 different normal human tissues, except Leydig cells in the testes and trace levels in a small percentage of normal breast tissue samples. The distinct and favorable expression profile of C35 spanning early through late stages of disease, including high frequency of overexpression in various breast carcinoma, abundant expression in distant metastases, and either absence or low level expression in normal human tissues, warrants further investigation of the relevance of C35 as a biomarker and/or a target for development of broadly applicable cancer-specific therapies. [Mol Cancer Ther 2006;5(11):2919–30]

Lethality-based selection of recombinant genes in mammalian cells: application to identifying tumor antigens.

Many biological processes result in either cell death or cessation of cell growth. However, plasmid- and retrovirus-based mammalian expression vectors in which it has been possible to construct representative cDNA libraries cannot be readily recovered from cells that are not actively dividing. This has limited the efficiency of selection of recombinant genes that mediate either lytic events or growth arrest. Examples include genes that encode the target antigens of cytotoxic T cells, genes that promote stem-cell differentiation and pro-apoptotic genes. We have successfully constructed representative cDNA libraries in a poxvirus-based vector that can be recovered from cells that have undergone lethality-based selection. This strategy has been applied to selection of a gene that encodes a cytotoxic T-cell target antigen common to several independently derived tumors.

The Relationship of CD5+ B Lymphocytes to Macrophages: Insights from Normal Biphenotypic B/Macrophage Cells

For decades, numerous investigators have reported derivation of macrophage-like cells from CD5+ pre-B cell lymphomas. Recently, it has become clear that biphenotypic CD5+ B/macrophage cells are not a spurious result of malignancy. Indeed, the existence of normal biphenotypic cells with CD5+ B lymphocyte and macrophage characteristics has been demonstrated in the mouse. This review considers normal B/macrophage cell function in an evolutionary context where a primitive, flexible cell type could perform dual roles in adaptive and innate immunity.

Proinflammatory Signals Upregulate COX-2 and Increase PGE2 Production in Biphenotypic B/Macrophage Cells

B-lymphocytes and macrophages are considered to be derived from separate lineages and to have specialized functions. However, it has been reported that certain malignant CD5+ B-lymphocytes are capable of differentiating to macrophage-like cells that express characteristics of both cell types.1 Differentiation to such biphenotypic cells has been termed lineage infidelity and has been found to be associated with a variety of diseases such as AIDS, Hodgkin’s lymphoma, and Sjögren’s syndrome.2 While all previous reports of cells exhibiting lineage infidelity had been confined to malignancies and other disease states, our lab has isolated a biphenotypic cell from normal mouse B-lymphocytes.3,4 These cells, called B/macrophage cells, are biphenotypic leukocytes generated from purified mouse B-lymphocytes incubated in mouse splenic fibroblast conditioned medium. B/Macrophage cells simultaneously express CD5+ B-lymphocyte (IgM, IgD, B220, CD5) and macrophage (phagocytosis, F4/80, Mac-1) characteristics. The function of these cells is unknown. The potential role of B/macrophage cells in inflammation and immune responses was explored by evaluating the expression of prostaglandin H synthase-1 (COX-1) and prostaglandin H synthase-2 (COX-2) and the production of PGE2. PGE2 is an important mediator in inflammatory responses. Synthesis of PGE2 is catalyzed by the cyclooxygenases, of which there are two isoforms, COX-1 and COX-2.5 COX-1 is constitutively expressed and is considered to be a housekeeping enzyme important for physiologic regulation. COX-2, on the other hand, is an inducible enzyme that can be upregulated after stimulation with certain cytokines, hormones, and lipid mediators. COX-1 and COX-2 expression are not detected in the starting population of B-lymphocytes. However, COX-1 and COX-2 mRNA are detectable after differentiation to the biphenotypic B/macrophage cells (FIG. 1). To confirm functional cyclooxygenase activity, PGE2 production was evaluated by immunoassay. B/Macrophage cells stimulated with LPS, anti-IgM, anti-IgM plus CD40L, and IFN-γ plus CD40L showed a significant increase in PGE2 production over the untreated sample (TABLE 1). To determine whether the PGE2 produced by these cells was synthesized mainly by COX-2, stimulated cultures were treated with