Monocytes contribute to the atherosclerotic cap by transformation into fibrocytes.

AIM: The stability of an atherosclerotic plaque is a key-determining factor in the clinical outcome of cardiovascular disease. In this respect, smooth muscle (SM) alfa actin positive cells play an important role in maintaining plaque stability through formation of a fibrous cap. Recent evidence suggests that circulating progenitors may be a source of these cells. We hypothesized that they may be fibrocytes bone-marrow derived cells that acquire SM-like characteristics, including the expression of SM alfa actin. METHODS: We examined human carotid endarterectomy specimens for the presence of fibrocytes by immunohistochemistry staining for CD34/procollagen I and leukocyte specific protein-1/procollagen I) and examined fibrocyte differentiation in vitro. RESULTS: Fibrocytes were found in regions of plaque growth/healing. They possessed a SM-like spindle shape, produced collagen, and consistent with being fibrocytes they co-localized with transformation growth factor beta, but not serum amyloid P factors, known to promote and inhibit their formation, respectively. While fibrocytes were detected in regions of new growth in 35/40 specimens, only 1/3 of the specimens expressed the SM cell marker calponin, and smoothelin was absent, in these regions. CONCLUSION: Our results demonstrate that fibrocytes contribute to formation of the fibrous cap. With fibrocytes being a monocyte derived cell, we suggest that monocytes may play a more crucial role in the clinical outcome of atherosclerosis than previously realized as they not only contribute directly to plaque instability (through foam cell formation), but also promote plaque stability by transformation into a fibrocyte.

Lack of increased expression of cell surface markers for circulating fibrocyte progenitors in limited scleroderma.

The aetiology and pathogenesis of scleroderma is incompletely understood. Recently, a cell called the fibrocyte has been shown to be derived from circulating monocytes with the ability to produce collagen. The aim of this study was to evaluate differences in the cell surface characteristics of circulating fibrocyte progenitors (monocytes) in patients with limited scleroderma compared to controls. A case-control study was performed in eight patients with limited scleroderma, which were matched with eight controls. Three-colour flow cytometry was used to assess the relative expression of cell surface markers. Statistical analysis then compared the relative expression between the two groups. In this preliminary study, there were no significant differences in the expression of circulating monocyte surface molecules involved with cell transformation, function, or migration presumed to give rise to fibrocytes, in a population of patients with limited scleroderma. Various explanations for the results are discussed.

The role of the fibrocyte in intimal hyperplasia.

BACKGROUND: Experimental animal studies have shown that the intimal hyperplasia (IH) responsible for occlusion after successful revascularization procedures may be partially caused by a bone marrow-derived cell that migrates to the site of vascular injury. Concurrent studies have demonstrated an extensive role in wound healing for the circulating fibrocyte. OBJECTIVES: We aimed to trace the path of the circulating cell that contributes to IH and determine if it is the fibrocyte. METHODS AND RESULTS: We established an in vitro model whereby purified monocytes from six healthy human volunteers were cultured into fibrocytes. These cells were morphometrically similar to the vascular smooth muscle cell (VSMC) found in IH and expressed alpha-smooth muscle actin (alpha-SMA) as well as CD34, CD45 and Collagen I (Col I), markers indicative of the fibrocyte. In an in vivo ovine carotid artery synthetic patch graft model, carboxyfluorescein diacetate, succinimidyl ester (CFSE) labeled circulating leukocytes were observed throughout the graft as well as in the neointima in 18 sheep. These cells were shown to produce collagen and alpha-SMA at 1, 2 and 4 weeks. These cells then underwent immunohistochemical analysis and were found to express a set of markers unique to the fibrocyte (CD34, CD45, Vimentin and alpha-SMA) and also to double stain for CD34 and alpha-SMA. CONCLUSIONS: IH in an ovine carotid artery patch graft model is partially derived from a hematopoietic circulating progenitor cell that acquires mesenchymal features as it matures at the site of injury.

A two-phase pathogenesis of graft-versus-host disease in mice.

Activation of donor T cells is required for the development of graft-versus-host disease (GVHD), a major complication of bone marrow transplantation. We investigated a murine model of GVHD across major and minor histocompatibility barriers. BALB/c recipients were lethally irradiated and transplanted with 10(7) bone marrow and 5 x 10(6) spleen cells from C57BL/6 donors. There were two separate phases of clinical disease. The first phase was most severe on day 7 after transplant. Weight and condition improved until day 12 and then a second phase of clinical GVHD commenced, which persisted until euthanasia. IL-2 mRNA expression, as a measure of T cell activation, was determined by quantitative PCR. The two phases of clinical GVHD were preceded by two separate peaks of IL-2 mRNA in the spleen. Host MHC class II(+) cells became undetectable by flow cytometry 7 days after transplantation, whereas donor MHC class II(+) cells increased during the first 9 days after transplantation. Removal of donor MHC class II(+) cells from the graft had no effect on the first phase. Possible roles for host and donor antigen-presenting cells (APC) in the two phases of the disease are discussed.

Administration of mycophenolate mofetil in a murine model of acute graft-versus-host disease after bone marrow transplantation.

BACKGROUND: Graft-versus-host disease (GVHD) remains the most significant obstacle to the use of allogeneic bone marrow transplantation as a treatment for leukemia and other hematological malignancies. Because current GVHD treatment regimens such as cyclosporine and methotrexate are only partially effective, there is a need for new immunosuppressive drugs for the treatment of this condition. METHODS: A recently developed immunosuppressive drug, mycophenolate mofetil (MM), was tested in a fully mismatched (C57BL/6 donors to BALB/c recipients) murine model of acute GVHD after bone marrow transplantation. RESULTS: A dose regimen of 30 mg/kg/day given by oral gavage and begun at 1 day before transplant had no positive effect on survival and was found to retard the rate of marrow engraftment as measured by absolute blood neutrophil counts. In all subsequent experiments, treatment was begun on day 5 after transplant. Three different doses (30, 60, and 90 mg/kg/day) were tested, but no significant improvement in mean survival time (MST) was observed for the first two doses (P=0.412 and 0.100, respectively). The highest dose (90 mg/kg/day) reduced MST (P=0.059), and no further dose increases were attempted. MM in combination with cyclosporine also failed to improve MST compared with animals treated with cyclosporine alone or controls. CONCLUSIONS: These results suggest that MM given orally is not effective in this murine model of GVHD and may not have a role in the treatment and prevention of acute GVHD arising from bone marrow transplantation in the clinical setting.

Effect of in vivo administration of IL-3 and IL-6, alone and in combination with G-CSF, GM-CSF or IL-1, on haematopoiesis, graft-versus-host disease and survival after murine haematopoietic stem cell transplantation.

We have explored the effect of IL-3 and IL-6, each alone and in combination with G-CSF, GM-CSF or IL-1, on neutrophil and platelet recovery in BALB/c mice (H-2d) given 10 Gy total body irradiation followed by 10(7) bone marrow cells and 10(6) spleen cells from C57BL6 donors (H-2b), as well as the effect of IL-3 alone and IL-6 alone on graft-versus-host disease (GVHD) and survival. Neither IL-3 alone nor IL-6 alone significantly increased the circulating absolute neutrophil count (ANC) at day 6 post transplant when compared with mice given saline injections (ANC 0.31 x 10(9)/l). G-CSF and IL-1, each alone, significantly raised the day-6 ANC (0.58 x 10(9)/l, p = 0.02; 0.67 x 10(9)/l, p = 0.007 respectively). However, IL-3, 200 ng twice daily, significantly increased the day-6 ANC when used in combination with GM-CSF (0.49 x 10(9)/l, p = 0.003) or with IL-6 (0.66 x 10(9)/l, p = 0.004), as well as with G-CSF (0.62 x 10(9)/l, p = 0.007) or with IL-1 (0.49 x 10(9)/l, p = 0.003). Apart from the combination with IL-3, IL-6 significantly raised the day-6 ANC only in combination with G-CSF (0.79 x 10(9)/l, p = 0.007). When used alone, both IL-6 and G-CSF raised the day-6 platelet count (312 x 10(9)/l, p = 0.02 and 309 x 10(9)/l, p = 0.01 respectively) compared with control mice (216 x 19(9)/l). IL-3 alone resulted in a platelet count of 303 x 10(9)/l (p = 0.06). In combination, only IL-3 with G-CSF significantly increased the value over that of saline control mice (328 x 10(9)/l, p = 0.02). IL-3 200 ng alone twice daily and IL-6 200 ng alone twice daily for 14 days post transplant resulted in survival not different from that of mice given saline injections. However, IL-3 500 ng twice daily for 14 days resulted in impaired survival and accelerated weight loss. In summary, while neither IL-3 nor IL-6 (nor GM-CSF) used alone accelerated neutrophil recovery post transplant, the combinations of IL-3 plus IL-6 and IL-3 plus GM-CSF did so. IL-6 (and G-CSF) accelerated platelet recovery post transplant, but combining IL-3 or IL-6 with the other cytokines was generally unsuccessful in this regard. Higher-dosage IL-3 appeared to accelerate graft-versus-host disease and impair survival, thus providing indirect evidence of the involvement of this cytokine in the mediation of GVHD.

A quantitative polymerase chain reaction assay for interleukin 5 messenger RNA.

The quantitation of low abundance messenger (m)RNA species such as that for interleukin 5 (IL-5) cannot be achieved by Northern blotting. Polymerase chain reaction (PCR) technology can be used to overcome this paucity of target molecules, but in its standard format it is semiquantitative. We describe the synthesis, purification, and use of a synthetic IL-5 mRNA (cRNA) molecule which, when included in the PCR reaction, enabled the amplification of IL-5 mRNA molecules from clinical samples to be made quantitative. A stringent protocol involving analysis of the purified transcript by PCR (to ensure its freedom from template molecules) is required. Preliminary experiments indicate that IL-5 mRNA levels are elevated in asthmatics.

In vivo administration of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF, interleukin-1 (IL-1), and IL-4, alone and in combination, after allogeneic murine hematopoietic stem cell transplantation.

BALB/c mice (H-2d) given 10 Gy total body irradiation (TBI) followed by 10(7) bone marrow (BM) and 10(6) spleen cells from C57BL/6 (H-2b) donor mice received recombinant cytokines intraperitoneally (IP) twice daily. The effect on neutrophil recovery rate, graft-v-host disease (GVHD), and survival was assessed. Four reagents were used: granulocyte-colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), interleukin-1 (IL-1) and IL-4, both alone and in combination. The most effective combination for increasing the circulating absolute neutrophil account (ANC) above the control value at day 7 posttransplant was the combination of G-CSF and IL-1 (mean ANC 2.4 +/- 1.6 x 10(9)/L as compared with control value of 0.07 +/- 0.05, P less than .02), followed by G-CSF alone (mean ANC 1.1 +/- 0.2, P less than .0001), the combination of GM-CSF plus IL-1 (mean ANC 0.8 +/- 0.3, P less than .002), and the combination of G-CSF plus GM-CSF (mean ANC 0.8 +/- 0.3, p less than .005). At day 10 posttransplant, the most effective combination in raising the ANC was the combination of G-CSF plus GM-CSF (mean ANC 7.5 +/- 2.3 as compared with control value of 3.5 +/- 1.1, P less than .01), followed by G-CSF alone (mean ANC 6.9 +/- 2.1, P less than .02). At the doses used, neither G-CSF nor GM-CSF had a deleterious effect on the incidence or severity of GVHD; indeed, GM-CSF was associated with improved survival. In contrast, IL-1 at doses greater than or equal to 100 ng twice daily caused marked early mortality, and there was a suggestion that IL-4 at doses of 500 ng twice daily resulted in increased late mortality, possibly owing to exacerbation of GVHD. This model appears to be of value for exploring the use of hematopoietic growth factors before they are used clinically in marrow allograft recipients.

Lymphocyte migration patterns in autoimmune MRL-lpr/lpr mice: relationship to age, disease manifestations and lymphocyte homing receptor expression.

We have previously reported that lymphoid cells from systemic lupus erythematosus (SLE) mice with established disease migrate aberrantly. This study evaluates the abnormal lymphocyte migration patterns found in MRL-lpr/lpr (MRL/l) mice in relation to age, disease manifestations and the expression of lymphocyte homing receptors. 51chromium-labelled lymph node cells from MRL/l and from normal histocompatible CBA mice of different ages were injected i.v. into age and sex-matched CBA recipients. Diminished lymph node and increased hepatic uptake of MRL/l compared to CBA cells was evident as early as 6 weeks of age. Abnormalities in lymphocyte migration antedated the appearance of elevated antihistone antibody (AHA) levels but not the development of lymphadenopathy. Using the monoclonal antibody MEL-14, no differences in the expression of lymphocyte homing receptors between MRL/l and CBA lymph node cells were found at any age. Thus abnormalities in lymphocyte migration in MRL/l mice appear as early as six weeks and are not related to changes in homing receptor expression.

Vasoconstrictor effects of uridine and its nucleotides and their inhibition by adenosine.

Uridine, uridine monophosphate (UMP) and uridine diphosphate (UDP) increased blood pressure when infused into intact anaesthetized rats and had similar effects on the perfusion pressure in the rat isolated perfused kidney. In an isolated vascular preparation, the everted rat portal vein, uridine was without effect while UMP and UDP caused log dose-related increases in contractile work. Adenosine infused at a dose of 200 nmol/kg per min blocked the response to uridine in the intact rat, converting it to a depressor response at higher doses, and reduced the response to UMP. Uridine may need to be phosphorylated to UMP to act on blood vessels. The two compounds are effective at similar dose ranges and suppress renin secretion in the isolated kidney, while UDP, which is effective at lower doses and stimulates renin secretion, may act by a different mechanism. Adenosine competes for membrane transport with uridine but its inhibition of the effects of UMP is consistent with activity at intracellular sites as well.