Identification of a subgroup of myelodysplastic patients with a neutrophil stimulation-signalling defect

Accumulation of an intron-retained mRNA for granulocyte macrophage-colony stimulating factor receptor common beta chain in neutrophils of myelodysplastic syndromes

We recently identified a reduction in the neutrophil surface expression of common beta chain (beta c) of the receptor for granulocyte macrophage-colony stimulating factor (GM-CSF) in the patients with myelodysplastic syndromes (MDS). To determine the etiology of the impaired beta c expression, beta c mRNA from neutrophilic granulocytes of MDS patients and healthy controls was analyzed by a combination of direct reverse transcriptase-polymerase chain reaction-based single-strand conformational polymorphism and sequencing. Nine different beta c transcripts were detected, but none was specific for MDS. However, one of the transcripts (beta c79) containing a 79-base intron insertion between exons V and VI was significantly increased in MDS. This 27-kd isoform consisted of the beta c N-terminal 182 amino acids followed by a new 84-amino-acid sequence. beta c79 was overexpressed in all MDS subtypes. No genomic mutations were detected within the intron or at the intron/exon boundaries. The isoform is predominantly located in the cytoplasm by Western blot analysis and was unable to generate high-affinity binding sites or transduce a signal for proliferation when coexpressed with the receptor for human GM-CSF alpha chain. Our study suggests that the accumulation of the abnormal beta c transcripts with intron V retention results in the reduction in cell-surface expression of beta c observed in MDS.

Cytokine priming of the granulocyte respiratory burst in myelodysplastic syndromes

Increased susceptibility to infections in patients with myelodysplastic syndromes (MDS) is thought to be due to neutropenia as well as functional abnormalities of neutrophils. In the present study we examined the effect of two different stimulants (fMLP, PMA) and three cytokines (alphaTNF, G-CSF and GM-CSF), both singly and in combination on granulocyte (RB) in 25 MDS patients compared to seven healthy controls. Single fMLP and PMA-stimulation showed similar results for both groups. Preincubation with cytokines enhanced fMLP-stimulated RB in most MDS patients and controls, but in patients to a significantly lesser extent when compared to the control group (p < or = 0,05). Combinations of alphaTNF + GM-CSF and alphaTNF + G-CSF were highly synergistic in priming fMLP-stimulated burst in both groups. But again, as with the single cytokine priming this effect was markedly reduced in MDS patients compared to controls (p < or = 0,05). A specific priming defect for one of the cytokines or a cytokine combination could not be demonstrated. Serum alphaTNF levels were measured in 18 and neutrophil alkaline phosphatase (NAP) index in 23 patients. Results did not correlate with variations of the RB in MDS patients. We conclude that reduced alphaTNF, GM-CSF and G-CSF priming of granulocyte RB is a frequent finding in MDS and may contribute to the enhanced susceptibility to bacterial infections.

Modulatory effects of the colonic milieu on neutrophil oxidative burst: a possible pathogenic mechanism of ulcerative colitis

An important hallmark of ulcerative colitis (UC) is mucosal neutrophil (PMN) infiltration associated with mucosal damage. This suggests that colonic chemoattractants such as bacterial products (e.g., N-formyl-methionyl-leucyl-phenylalanine (fMLP), lipopolysaccharide (LPS)) reach systemic circulation and attract PMNs to the colon. PMNs are then activated in the colonic mucosa and release their toxic oxidative metabolites. However, bacterial products are also present in the systemic circulation of healthy subjects. Thus we hypothesized that PMNs develop tolerance to colonic factors in the normal state and that this tolerance is absent in UC. We evaluated the PMN respiratory burst in response to stimulation with fMLP, LPS, or phorbol 12-myristate 13-acetate (PMA) by measuring the production of reactive oxygen species (ROS) with both luminol-enhanced chemiluminescence and a cytochrome C reduction assay. PMNs were obtained from control subjects, inactive UC patients, patients with UC who had undergone colectomies, and non-UC patients with colectomies. All three stimuli induced a significant rise in ROS. PMNs from non-UC colectomy subjects produced significantly higher ROS than PMNs from control subjects with intact colons in response to both fMLP and LPS. In contrast, PMNs from UC colectomy patients produced levels of ROS similar to those produced by PMNs from UC patients with intact colons in response to fMLP and LPS. Colectomy had no effect on PMA-induced ROS production in controls. The observed difference in fMLP-induced ROS production in control subjects with intact colons was not due to fMLP receptor down-regulation because a competition assay performed with the fMLP blocker BMLP showed a similar receptor apparent affinity in all four groups. We conclude the following: (1) the normal colonic milieu modulates the PMN respiratory burst, resulting in hyporesponsiveness of PMNs to "physiologic" but not "pharmacologic" stimulation. This effect is not due to receptor down-regulation. (2) UC colonic milieu does not appear to modulate PMN respiratory burst. This loss of PMN "tolerance" to colonic factors may have a pathogenic role in the sustained inflammation and tissue damage in UC.

Actin polymerization in neutrophils from patients affected by myelodysplastic syndromes--a flow cytometric study

In this study F-actin polymerization in neutrophils from 21 patients affected by myelodysplastic syndromes (MDS) was evaluated by means of a flow cytometric assay. Neutrophils were stimulated with formyl-methionyl-leucyl-phenylanaline (fMLP; 10(-8) M final concentration) for 15, 30, 60 and 120 sec, and F-actin content was determined using fluorescein-isothiocyanate phallacidin as a specific probe. Eight normal subjects were studied as controls. We found that F-actin polymerization was defective in ten patients, with very impaired values after 60 and 120 sec of stimulation with fMLP. The remaining 11 patients showed a prevalent neutrophil population with normal F-actin polymerization and neutrophil sub-populations with either defective or undetectable F-actin polymerization. In the first group, patients with very poor prognosis (refractory anemia with excess blasts, refractory anemia with excess blasts in leukemic transformation, trisomy 8, multiple karyotypic abnormalities) were present, although patients with aberrations of karyotype were present in the second group. It is possible that defects in neutrophil F-actin polymerization may be responsible for neutrophil dysfunction, which has frequently been observed in MDS.

Luminol-enhanced, whole blood chemiluminescence of human neutrophils evaluated by means of an automated, computer-assisted, and high-sensitivity luminescence analyzer

Luminol-enhanced whole blood chemiluminescence of human neutrophils was studied using opsonized zymosan as a stimulus. Heparinized blood (0.5 microliters) was used, and the chemiluminescence signals were recorded by a very sensitive, automated, and computer-assisted luminometer (LB 950, Berthold, Wildbad, Germany). The following parameters were provided: integral values over the total measuring time, peak values, the time to reach maximum value, and the time to reach half maximum value. Normal subjects, neutropenic patients, subjects with total or partial myeloperoxidase deficiency, patients with recurrent infections, phagocytic defects, thrombocythemic patients and those with non-Hodgkin's lymphomas undergoing therapy with recombinant human granulocyte colony-stimulating factor were studied. The integral response of chemiluminescence and the time of reach half maximal value were useful indicators of chemiluminescence defects; the assay, was able to detect chemiluminescence responses in neutropenic subjects with neutrophil levels as low as 0.6 x 10(9)/l; differences between cellular and plasma defects could be identified; the quenching effect exerted by erythrocytes was negligible.

Impaired activation of phospholipase D in polycythaemia vera-implications for the pathogenesis of the disease?

A series of studies have demonstrated a stimulus-specific defect in PMN oxidative metabolism after stimulation with surface receptor dependent stimuli such as fMLP, leukotriene B4 and platelet activating factor (PAF), whereas the response to phorbol myristate acetate was normal. Having discovered this defect, studies of the stimulus response coupling for oxidative responses were performed showing a normal interaction of fMLP with it's receptor, as well as an intact activation of phospholipase C, as measured by the generation of 1,4,5-inositoltrisphosphate, and the subsequent rise of intracellular calcium. In contrast, the formation of diacylglycerol and phosphatidylethanol was decreased in PV PMN, denoting an impaired activation of phospholipase D (PLD). It was shown by flow cytometry analyses that the hampered oxidative response was present both in single PMN and monocytes. Moreover, platelets from PV patients, whose PMN exhibit a lower oxidative response to PAF, also have a diminished aggregatory response to PAF. Thus three different cell lineages in PV have been revealed to respond abnormally to surface receptor dependent stimuli, indicating that the proposed impairment of PLD might be relevant for changes in the malignant stem cell clone. Since phosphatidic acid, produced as a result of PLD activation, may be implicated in the regulation of several oncogenes, perturbations of the PLD system could theoretically be important for the development of PV.