Interactions between platelets and neutrophils in essential thrombocythaemia. Effects on neutrophil chemiluminescence and superoxide anion generation.

Essential thrombocythaemia (ET) is frequently associated with neutrophil and platelet dysfunction, and with increased incidence of vascular complications (thrombosis, haemorrhage). Several interactions between platelets and neutrophils have been reported, and the reciprocal actions between these cells may have an important role both in thromboregulation and in diseases such as those caused by uncontrolled neutrophil activation. In the current paper the authors studied 15 patients affected by ET and 10 normal subjects as controls. Circulating neutrophils and platelets were purified and were recombined in constant ratios (50:1, 100:1 and 200:1) and the individual platelet to neutrophil ratio. Superoxide anion (O2-) generation and luminol-enhanced chemiluminescence (CL) were studied after neutrophil stimulation with fMLP. In normal subjects both O2- generation and CL were inhibited by autologous platelets in a dose-dependent manner. In ET patients, on the contrary, platelet-dependent inhibition of O2- generation did not occur, while a dose-dependent inhibition of CL was observed. Two groups of ET patients were found: patients with neutrophil O2- generation and CL within the normal range, and patients with significantly reduced neutrophil respiratory burst. However, no differences were found between these two groups of patients in terms of platelet effects towards fMLP-stimulated neutrophils. Therefore, platelets from ET patients were not able to exert the homeostatic control towards neutrophil O2- generation shown by platelets from normal subjects, and this phenomenon may have a role in the clinical setting. In fact, O2- has been shown to be a very strong direct platelet activator, is able to inactivate nitric oxide (which is a powerful inhibitor of platelet aggregation and adhesion to endothelium), and is directly involved in neutrophil-mediated tissue damage.

Platelet-neutrophil interactions in uremic patients: effects on neutrophil superoxide anion production and chemiluminescence.

Isolated resting platelets are able to limit neutrophil activation and then can control the tissue-damaging potential of activated neutrophils. In the present study, platelet-neutrophil interactions have been evaluated in 10 uremic patients; the blood samples have been collected before the hemodialysis session. Twelve normal subjects served as controls. Platelets and neutrophils have been isolated and recombined in an autologous ex vivo system. Anion superoxide production and chemiluminescence (which is related to hypochlorous acid production) have been evaluated after stimulation with N-formyl-methionyl-leucyl-phenylalanine. Coincubation of platelets from normal subjects with autologous neutrophils led to a dose-dependent inhibition of both superoxide anion generation induced by N-formyl-methionyl-leucyl-phenylalanine and chemiluminescence. Instead, platelets from uremic patients have not affected superoxide anion production by autologous neutrophils. The chemiluminescence was reduced by coincubation with autologous platelets only at the highest platelet-neutrophil ratio (100:1). In conclusion, the modulation exerted by platelets towards neutrophil activation can be impaired in chronic uremia. Therefore, the tissue-damaging potential of circulating neutrophils, due to toxicity by superoxide anion and hypochlorous acid, may be increased.

Neutrophil functions in essential thrombocythemia.

Chronic myeloproliferative diseases, such as chronic myeloid leukemia and polycythemia vera, are associated with neutrophil dysfunction. Very little data is available on essential thrombocythemia (ET). In the current study we evaluated 21 patients with ET. All patients were studied at least 16 weeks after any cytostatic therapy and 10 days after any other therapy. Neutrophil functions were investigated as follows: flow cytometric evaluation of whole blood phagocytosis of opsonized FITC-conjugated E. coli; whole blood chemiluminescence after stimulation with opsonized zymosan and evaluation by an automated, computer-assisted luminometer (LB 950, Berthold); and chemiluminescence and superoxide anion generation by purified neutrophils after f-MLP and PMA stimulation. Chemiluminescence and superoxide anion generation after f-MLP stimulation were found to be significantly lower than in normal subjects, whereas values within the normal ranges were registered after PMA stimulation. Phagocytosis-associated chemiluminescence was found to be impaired both by using zymosan opsonized with autologous plasma and zymosan opsonized with normal plasma, despite a normal phagocytic activity. These data show the presence in ET of a complex neutrophil dysfunction that may be related to an impaired signal transduction during both the phagocytic process and f-MLP stimulation.

IgE modification of the specific antidermatophagoides during the first year of specific immunotherapy (SIT).

Six subjects (4 female, 2 male), aged from 16 to 25 years, presented with allergic rhinitis to Dermatophagoides mites and received SIT by the sub-cutaneous route with delayed-release alpha fraction Bayropharm at the standard doses. Diagnosis was based on clinical history, skin tests and measurement of specific IgE at 0, 3, 9, and 12 months, by the fluoro-enzymatic technique (FAST). For comparison, in a reference group (n = 20) the IgE varied between 0.32 and 0.11 IU/ml for D1 and 0.31 to 0.09 IU/ml for D2. The eight patients had specific IgE titres of D1 = 0.96, D2 = 0.99. For these authors, the FAST technique used for the measurement of specific IgE, although less sensitive than the RIA technique of RAST, gives a good evaluation of SIT.

FcRIII (CD16) expression on neutrophils from chronic myeloid leukemia. A flow cytometric study.

FcRIII (CD16) expression on neutrophils from 17 patients with chronic myeloid leukemia (CML) was studied by flow cytometry using monoclonal antibodies. A variable proportion of CD16-negative neutrophils were found both in CML patients in chronic phase (3 out of 8 patients) and in CML patients in hematological remission (3 out of 9 patients). Neutrophils with reduced FcRIII expression showed more defective chemiluminescence and phagocytosis than neutrophils with normal FcRIII expression. Circulating myeloid cells from three patients in chronic phase, showing a normal percentage of CD16-positive neutrophils, were isolated and fractionated by discontinuous Percoll gradients. This study showed that CD16 appears at the stage of metamyelocyte, that band cells and segmented neutrophils display an identical pattern of membrane FcRIII, and that the fluorescence intensity shown by metamyelocytes is different from that displayed by more mature cells. The association between low FcRIII expression and function abnormality could be suggestive of a defect in CML neutrophil maturation.