Aberrant T-cell antigen expression in B lymphoblastic leukaemia.

B lymphoblastic leukaemia (B-ALL) cells are characterized by the expression of various B-cell antigens. Expression of T/Natural Killer-cell antigens, however, has rarely been reported in B-ALL (TAg+ B-ALL), and the significance of this aberrant antigen expression is unclear. We thus analysed the frequency of TAg+ B-ALL at our institution and investigated its significance in the context of immunophenotypes, cytogenetic/molecular findings, and prognosis. We reviewed 134 consecutive cases of B-ALL and found 18 cases (13·4%) of TAg+ B-ALL. The most common aberrant T-cell antigens expressed were CD2, CD5, and CD7 at equivalent rates (each in six cases), CD4 (two cases), and CD56 (three cases). Adverse cytogenetic abnormalities were seen in a significantly larger proportion of the TAg+ cases (72·2%) than the TAg- cases (32·2%; P = 0·003). Multivariate Cox-regression analysis showed that the risk of relapse over time was higher in the TAg+ cases, independent of high risk status (based on age and white blood cell count) and the presence of adverse cytogenetic abnormalities (hazard ratio = 2·256, P = 0·065). These findings suggest that T-cell antigen expression in B-ALL may be an independent predictor of poor prognosis, and a useful marker to identify patients at increased risk for relapse and for harbouring adverse cytogenetic abnormalities.

Platelet adhesion to human vascular endothelium is modulated by constitutive and cytokine induced nitric oxide.

OBJECTIVE: The aim was to study whether basal or cytokine stimulated generation of nitric oxide (NO) modulates platelet adhesion to human umbilical vein endothelial cells (HUVEC). METHODS: The adhesion of 111In labelled human platelets to transfected HUVEC (SGHEC-7) was measured either alone or after incubation of SGHEC-7 cells for 18 h with interleukin-1 beta (IL-1 beta) and/or tumour necrosis factor alpha (TNF alpha). The activity of NO synthase in these cells was measured by formation of citrulline. The effects of dexamethasone (0.3 microM) and NG-monomethyl-L-arginine (L-NMMA, 100 microM) on these two variables were determined. RESULTS: Stimulation of SGHEC-7 cells with IL-1 beta or TNF alpha (each at 1-30 ng.ml-1) caused them to express the inducible NO synthase, an effect that was prevented by dexamethasone. Platelet adhesion to unstimulated SGHEC-7 cells was < 0.1% (n = 3) and was increased to 0.7 (SEM 0.2)% by L-NMMA but was not affected by dexamethasone. Stimulation of the cells with IL-1 beta and TNF alpha increased platelet adhesion to a maximum of 2.2(0.4)%. This increase was enhanced by both dexamethasone and L-NMMA. The effect of L-NMMA was prevented by L-arginine. CONCLUSIONS: Inhibition of NO synthesis by L-NMMA potentiates platelet adhesion to unstimulated SGHEC-7 cells, showing that basally released NO regulates platelet adhesion. Stimulation of SGHEC-7 cells by cytokines increases their adhesive properties but at the same time causes them to express the inducible NO synthase. Nitric oxide generated by this enzyme contributes to the modulation of the adhesive properties of the endothelial cells. Thus both constitutive and inducible NO synthases modulate endothelial cell thrombogenicity.

Transcellular regulation of cell respiration by nitric oxide generated by activated macrophages.

A macrophage cell line (J774), activated with interferon-gamma and endotoxin to express the inducible form of NO synthase (iNOS), immediately inhibited the cellular respiration of co-incubated L-929 fibroblasts or non-activated J774 macrophages. The inhibition was potent, rapid and reversible when the NO was removed by adding oxyhaemoglobin or by inhibiting iNOS. Exogenously added NO also rapidly and reversibly inhibited cellular respiration over the same range of NO concentrations. This inhibition was competitive with oxygen and due to direct inhibition of cytochrome oxidase. Thus, NO generated by one cell can regulate the respiration of adjacent cells, supporting the hypothesis that NO may be a physiological and/or pathological regulator of cellular respiration, via its inhibition of cytochrome oxidase.

The role of nitric oxide in endothelial cell damage and its inhibition by glucocorticoids.

Incubation of vascular endothelial cells with S.typhosa endotoxin and interferon-gamma caused a time- and concentration-dependent reduction in the viability of the cells. The cytotoxic effect was inhibited in a concentration-dependent manner by NG-monomethyl-L-arginine, an inhibitor of nitric oxide (NO) synthesis, and by the glucocorticoids dexamethasone and hydrocortisone, two inhibitors of the induction of NO synthase. These findings indicate that in these cells the cytotoxic effect of endotoxin is mediated by the NO synthesized by an inducible NO synthase. This induction of NO synthase in vascular endothelial cells may represent a mechanism of local endothelial damage during endotoxin shock and other immunologically based conditions.

Functional evidence for nitrergic neurotransmission in a human clitoral corpus cavernosum: a case study.

Although the presence of neuronal nitric oxide synthase (nNOS) has been demonstrated in human clitoral corpus cavernosum, functional evidence for the nitrergic neurotransmission as a nonadrenergic noncholinergic (NANC) transmitter has been limited to animal studies. Here we show that electrical field stimulation elicited reproducible NANC relaxation responses in a clitoral corpus cavernosum, obtained from a 38-y-old woman undergoing clitoral reduction surgery. These relaxation responses were abolished by an inhibitor of NO synthase or tetrodotoxin proving that they were nitrergic in nature and neuronal in origin. Large and small calibre nitrergic nerves were demonstrated with immunohistochemistry using nNOS antibody, which were also immunostained with cholinergic nerve markers. nNOS expression was confirmed using Western blotting. This is the first report to show that NO produced by nNOS within the cholinergic-nitrergic nerves is responsible for the NANC relaxation responses in a human clitoral corpus cavernosum.

Spectrum of childhood Epstein-Barr virus-associated T-cell proliferations and bone marrow findings.

Systemic Epstein-Barr virus-positive (EBV+) T-cell lymphoproliferative disorder of childhood is a recently described entity. The majority of such cases have been reported from Asia, which suggests an underlying genetic predisposition. We analyzed the clinicopathologic characteristics of 5 children with EBV+ T-cell lymphoid proliferations evaluated and treated at our institute over a 2-year period. There were 3 males and 2 females of Latino (n  =  4) or Caucasian (n  =  1) heritage with a median age of 5 years (age range 2-18 years). All patients presented with EBV infection (acute, n  =  4) with elevated serum EBV viral loads at the time of diagnosis and had systemic manifestations, including fever, hepatosplenomegaly, and pancytopenia. The bone marrow biopsies showed EBV+/CD8+ T-cell lymphocytosis in all patients, with variable degrees of histiocytosis, plasmacytosis, and hemophagocytosis. Interestingly, there was marked and consistent depletion of mature and precursor B cells in the marrow (<1% of total marrow cellularity) in all patients. Three of the patients died of disease-associated complications 2 to 12 weeks after initial diagnosis. Our study describes the detailed bone marrow findings, contributes to the growing number of cases of systemic EBV+ T-cell lymphoproliferative disorder of childhood occurring in the Western hemisphere, and documents this disorder in patients from the Caribbean countries.

Hematogones: a review and update.

Our knowledge regarding the nature and function of 'hematogones' has evolved considerably, since the initial description more than 70 years ago. Once considered the 'mystery cells' of the bone marrow, major advances in immunology and flow cytometry have enabled us to better characterize these cells and recognize them as physiologic precursors of B-cells. In this review, we describe the morphologic and phenotypic characteristics and clinical relevance of hematogones, and report recent advances in our understanding and knowledge of these cells as they relate to physiologic and different pathologic conditions.

FISH analysis in addition to G-band karyotyping: utility in evaluation of myelodysplastic syndromes?

Cytogenetic analysis provides important diagnostic and prognostic information for patients with myelodysplastic syndromes (MDS). Prior studies, mostly comprised of small sample sizes, have reported conflicting results while evaluating the usefulness of FISH in addition to G-band karyotyping in MDS. In the current study, the utility of performing a tailored FISH panel, in addition to G-band karyotyping was evaluated in a series of 110 MDS patients diagnosed at our institute. Using our FISH panel, clonal cytogenetic abnormalities were detected in 3/8 (38%) of MDS cases with karyotype failure and in 5/54 (9%) cases with normal G-band karyotypes, all the latter had intermediate or high grade MDS. Of the cases with abnormal G-band karyotypes, 6/48 (13%) showed discrepancies between FISH and G-band results, however, FISH analysis only lead to reassignment of karyotypic abnormalities to different chromosomes, MDS cytogenetic risk stratification was not altered. Our findings suggest that FISH testing is informative only in MDS cases with karyotype failure and intermediate-high grade MDS cases with normal G-band karyotype and has limited utility in cases that have normal G-band karyotypes and morphologic features of low grade MDS or in cases with abnormal G-band karyotypes.

Hematogones are markedly reduced in pediatric acquired aplastic anemia: multiparametric flow cytometric analysis.

Acquired aplastic anemia (AA) and myelodysplastic syndromes (MDS) are bone marrow (BM) failure syndromes with overlapping clinical features, and at least a subset appears to share common pathophysiologic mechanisms. Recent studies of MDS have shown down-regulation of genes involved in B-cell development and decreased B-cell precursors (hematogones). We explored the possibility that AA, similar to MDS, might also be associated with defects in development of lymphoid cells, especially B-cells, by using flow cytometry to assess the presence of hematogones and mature lymphocytes in BM samples from 25 children with AA and 41 age-matched controls. We observed that the percentage of total and early (stage I) hematogones were significantly decreased in AA compared to controls, and they returned to normal numbers after hematopoietic stem-cell transplant. This demonstrates early B-cell lineage involvement in AA, similar to recent findings in MDS. Our findings suggest dysfunction of an early multilineage progenitor in the pathogenesis of AA.

On the mechanism by which vascular endothelial cells regulate their oxygen consumption.

Two enzymes, soluble guanylyl cyclase and cytochrome c oxidase, have been shown to be exquisitely sensitive to nitric oxide (NO) at low physiological concentrations. Activation of the soluble guanylyl cyclase by endogenous NO and the consequent increase in the second messenger cyclic GMP are now known to control a variety of biological functions. Cytochrome c oxidase, the terminal enzyme of the mitochondrial respiratory chain, is inhibited by NO. However, it is not clear whether NO produced by the constitutive NO synthase interacts with cytochrome c oxidase, nor is it known what the biological consequences of such an interaction might be. We now show that NO generated by vascular endothelial cells under basal and stimulated conditions modulates the respiration of these cells in response to acute changes in oxygen concentration. This action occurs at the cytochrome c oxidase and depends on influx of calcium. Thus, NO plays a physiological role in adjusting the capacity of this enzyme to use oxygen, allowing endothelial cells to adapt to acute changes in their environment.

Glucocorticoids do not affect the induction of a novel calcium-dependent nitric oxide synthase in rabbit chondrocytes.

Incubation of rabbit articular chondrocytes with interleukin-1 beta caused time-dependent expression of NO synthase, determined as nitrite, after a lag period of 6h. The synthesis of nitrite was concentration-dependent and was inhibited by cycloheximide and NG-monomethyl-L-arginine, but not by dexamethasone or hydrocortisone. The synthesis of NO in the 100,000g supernatant of activated chondrocytes was inhibited by EGTA, but not by the calmodulin inhibitors W-13 or trifluoperazine. The synthesis of NO was half-maximal at approximately 20nM free Ca2+. Endotoxin also induced the expression of this NO synthase. Thus, rabbit articular chondrocytes express a novel inducible NO synthase which is Ca(2+)-dependent, and whose induction is not prevented by glucocorticoids.

Visualisation of nitric oxide generated by activated murine macrophages.

We have visualised the release and approximate diffusion profile of nitric oxide (NO) from activated murine macrophages using a high transmission microscope coupled to a high sensitivity photon counting camera. The images generated by NO were cell-associated and spread over an area of approximately 175 micrometers from the activated macrophage. The signals obtained were dependent on the presence of exogenous L-arginine in the medium and followed a time course similar to that previously described for the generation of NO by the inducible form of NO synthase. The light signal was attenuated by the inhibitor of NO synthase, N omega-nitro-L-arginine methyl ester. Studies using superoxide-deficient macrophages further confirmed that the signals detected were generated by NO rather than reactive oxygen intermediates.

A lethal role for lipid A in Salmonella infections.

Salmonella infections in naturally susceptible mice grow rapidly, with death occurring only after bacterial numbers in vivo have reached a high threshold level, commonly called the lethal load. Despite much speculation, no direct evidence has been available to substantiate a role for any candidate bacterial components in causing death. One of the most likely candidates for the lethal toxin in salmonellosis is endotoxin, specifically the lipid A domain of the lipopolysaccharide (LPS) molecule. Consequently, we have constructed a Salmonella mutant with a deletion-insertion in its waaN gene, which encodes the enzyme that catalyses one of the two secondary acylation reactions that complete lipid A biosynthesis. The mutant biosynthesizes a lipid A molecule lacking a single fatty acyl chain and is consequently less able to induce cytokine and inducible nitric oxide synthase (iNOS) responses both in vivo and in vitro. The mutant bacteria appear healthy, are not sensitive to increased growth temperature and synthesize a full-length O-antigen-containing LPS molecule lacking only the expected secondary acyl chain. On intravenous inoculation into susceptible BALB/c mice, wild-type salmonellae grew at the expected rate of approximately 10-fold per day in livers and spleens and caused the death of the infected mice when lethal loads of approximately 10(8) were attained in these organs. Somewhat unexpectedly, waaN mutant bacteria grew at exactly the same rate as wild-type bacteria in BALB/c mice but, when counts reached 10(8) per organ, mice infected with mutant bacteria survived. Bacterial growth continued until unprecedentedly high counts of 10(9) per organ were attained, when approximately 10% of the mice died. Most of the animals carrying these high bacterial loads survived, and the bacteria were slowly cleared from the organs. These experiments provide the first direct evidence that death in a mouse typhoid infection is directly dependent on the toxicity of lipid A and suggest that this may be mediated via pro-inflammatory cytokine and/or iNOS responses.