Streptococcal erythrogenic toxins induce neopterin formation in human peripheral blood mononuclear cells but not in the human myelomonocytoma cell line THP-1

Inflammatory biomarker, neopterin, predominantly enhances myelopoiesis, which suppresses erythropoiesis via activated stromal cells

Neopterin is produced by monocytes and is a useful biomarker for inflammation. We found previously that neopterin enhanced myelopoiesis but suppressed B-lymphopoiesis triggered by the positive and negative regulations of cytokines produced by stromal cells in mice. The effects of neopterin on erythropoiesis during the enhancement of myelopoiesis were determined in the present study using C57BL/6J mice. The intravenous injection of neopterin into mice resulted in a prolonged decrease in the number of femoral erythroid progenitor cells (BFU-Es and CFU-Es), whereas the number of femoral myeloid progenitor cells (CFU-GMs) was increased. Interestingly, the oscillatory changes in the number of erythroid progenitor cells were reciprocal to those of myeloid progenitor cells. The expression of Cdc42, a regulator of the balance between erythropoiesis and myelopoiesis, was down-regulated, implying that the suppression of erythropoiesis is due to myelopoietic predominance. Furthermore, the expression of SDF-1 in stromal cells, a negative regulator of erythropoiesis, was up-regulated. These results suggest that neopterin facilitates myelopoiesis in the bone marrow by suppressing erythropoiesis, thereby contributing to the potential up-regulation of inflammatory process.

Inflammatory biomarker, neopterin, enlarges splenic mast-cell-progenitor pool: Prominent impairment of responses in age-related stromal cell-impairment mouse SCI/SAM

Neopterin is produced by monocytes and is a useful biomarker of inflammatory responses. We found that neopterin enhances granulopoiesis, but suppresses B-lymphopoiesis triggered by the positive and negative regulations of cytokines produced by stromal cells in mice. In this study, neopterin was found to regulate mast cell development, which was confirmed in the mouse model of senescent stromal-cell impairment (SCI). In non-SCI mice (=less senescent stage of SCI mice), neopterin decreased the number of colonies of IL-3-dependent mast-cell progenitor cells (CFU-mast) from unfractionated bone-marrow cells, but not that from the lineage-negative bone-marrow cell population without stromal cells in a semisolid in vitro system. Neopterin increased the gene expression and protein production of TGF-beta, a negative regulator of CFU-mast, in cultured stromal cells, indicating that neopterin suppressed CFU-mast colony formation by inducing TGF-beta in stromal cells. In contrast to this in vitro study, in vivo treatment with neopterin did not significantly up-regulate TGF-beta. The intravenous injection of neopterin into mice decreased the number of femoral CFU-mast and the expression level of the gene for stem cell factor (SCF), a positive regulator of CFU-mast, whereas the number of splenic CFU-mast and SCF gene expression level increased. In SCI mice, the in vivo and in vitro responses of mast cell development and cytokine gene expression level to neopterin treatment were less marked than those in non-SCI mice. These results suggest that, firstly, neopterin augments the splenic pool of CFU-mast by the production of SCF, and secondly, such neopterin function becomes impaired during senescence because of an impaired stromal-cell function, resulting in the down-modulation of host-defense mechanisms.

Interferon-gamma-primed monocytoid cell lines: optimizing their use for in vitro detection of bacterial pyrogens

In order to reduce animal testing for quality control of pharmaceutical agents intended for parenteral use, the Limulus amebocyte lysate (LAL) assay is now being accepted in many cases as an alternative to measuring pyrogenic activity of samples in rabbits. However, since the LAL test is specific for cell wall components from Gram-negative bacteria and is sometimes difficult to perform in samples containing large amounts of protein, this alternative still leaves a considerable diagnostic gap. Here, we have optimized a previously established test based on assessing the formation of neopterin or nitrite in interferon-gamma-treated human (THP-1) or murine (J774A.1, RAW264.7) monocytoid cell lines, respectively, in response to bacterial pyrogens. Optimal results were obtained either with THP-1 cells in serum-containing media and using a high concentration of interferon-gamma (IFN-gamma) or with RAW264.7 cells in serum-free media and independent of the IFN-gamma dose. Results were significantly correlated with those obtained by another cell-culture-based assay in which formation of tumor necrosis factor-alpha by THP-1 1G3 cells was assessed. Also in RAW264.7 murine monocytoid cells, formation of nitrite and of tumor necrosis factor-alpha in response to a variety of samples was correlated. Samples shown to be pyrogenic in rabbits in a previous study were unambiguously detected with the test presented here. As expected, the LAL test was negative with cell-free supernatants from Staphylococcus aureus66 kDa). Taken together, these results indicate that the use of monocytoid cell lines and the detection of metabolites which are triggered in the course of immunostimulation could fill the gap left by the LAL test and help to further reduce animal testing for pyrogens.

Neopterin: a review

Neopterin was discovered in bee larvae, in worker bees and in royal jelly. The compound was termed "neopterin" to denote that it might start a new (Greek, neo) epoch in pteridine research. Increased concentrations of neopterin were reported in patients with viral infections, suggesting that increased neopterin may originate from the immune response of patients to the infections. In vitro studies revealed that human monocytes/macrophages produce neopterin when stimulated by interferon-gamma. Neopterin can easily be detected in serum and urine. The most important clinical applications for the determination of neopterin are prognostic indicator of malignant diseases, follow-up control of chronic infections, monitoring of immune-stimulatory therapy, differential diagnosis of acute viral and bacterial infections, prognostic indicator in HIV infections and early indications of complications in allograft recipients. In recent years new physiological functions of neopterin have been discovered such as inducing or enhancing cytotoxicity, inducing apoptosis and the role of a chain breaking antioxidant. This review will focus on the immunological and physiological properties of neopterin.