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PubMed1986

Characterization of human platelet basic protein, a precursor form of low-affinity platelet factor 4 and beta-thromboglobulin.

Platelet basic protein (PBP) was purified from the supernatant of thrombin-stimulated, washed human platelets by ion-exchange, affinity, molecular sieve, and high-performance liquid chromatography (HPLC). The NH2-terminal amino acid sequence was determined by automated Edman degradation, revealing 9 unique residues followed by 10 residues of the established low-affinity platelet factor 4/beta-thromboglobulin (LA-PF4/beta TG) sequence. Among the nine were three basic residues, accounting for the high isoelectric point of PBP. Additional evidence for precursor status includes the immunological cross-reactivity of all three species and the ability of plasmin and trypsin to produce from PBP a species resembling beta TG in charge, hydrophobicity, and size. Tryptic peptide maps of PBP and LA-PF4 obtained by reverse-phase HPLC were very similar, and from each protein, a peptide was isolated which showed the amino acid composition predicted for the COOH-terminal tryptic peptide of beta TG. Normal platelets contained predominantly LA-PF4, with PBP ranging from 10% to 30% of total beta TG antigen. This was true even when fresh platelets were lysed with trichloroacetic acid in order to provide the most complete and rapid inhibition of proteolytic activity. beta TG itself was never detected in this situation or in the release supernatant of stimulated platelets, and only rarely in unprotected lysates. In agreement with earlier results, crude preparations of PBP were mitogenic for 3T3 cells, but highly purified preparations of PBP and LA-PF4 were free of this activity.

Amino Acid Sequence↗
PubMed1989

Muscle contraction headache and migraine. Platelet activation and plasma norepinephrine during the cold pressor test.

For clarification of possible platelet activation in migraine and chronic muscle contraction headache (MCH) under stress, plasma platelet factor 4 (PF4), norepinephrine (NE), and free fatty acids (FFA) were investigated during the cold pressor test. Both PF4 and NE increased significantly, whereas FFA showed no remarkable changes. The increases of PF4 in MCH and migraine during this test were significantly greater than in healthy controls. The increase of PF4, however, was independent of NE increase and FFA changes. On the other hand, we observed decreased NE levels in both MCH and migraine, which might suggest peripheral sympathetic hypofunction. The platelets of MCH or migraine patients seem to be impaired, and the impairment may be caused by continuous sympathetic hypofunction. The behaviour of the above three substances in MCH was similar to that in migraine throughout the present study.

Blood Platelets↗
PubMed1986

Protease-induced immunoregulatory activity of platelet factor 4.

Intravenous injection of human or mouse serum or platelet material secreted from appropriately stimulated platelets ("releasate") together with antigen alleviates the immunosuppression in SJL/J mice induced by injection of irradiated lymphoma cells or in (CB6)F1 mice induced by injection of concanavalin A. We now report that injection of releasate from 10(6) human platelets restores plaque-forming cells to the unsuppressed number; greater amounts increase responses further. Immunoregulatory activity is released from platelets exposed to thrombin in parallel with other alpha-granule components. Heparin-agarose absorbs activity. Purified platelet factor 4 (PF4) has activity; beta-thromboglobulin and platelet-derived growth factor have little or none. Activity in serum is neutralized by goat anti-human PF4. An enzymatic step is necessary for production of immunoregulatory activity. Releasates boiled immediately after platelet aggregation with 250 nM A23187 or those produced by adding A23187 in the presence of 100 microM serine protease inhibitor (p-amidinophenyl)methanesulfonyl fluoride (APMSF) are ineffective, whereas releasates boiled or mixed with APMSF after incubation for 60 min are active. Activity is generated by incubating a mixture of heparin-absorbed releasate (as enzyme source) and heparin-agarose eluate of releasate made in the presence of APMSF (as substrate source). The enzymatic step does not alter the heparin-neutralizing activity of PF4. Apparently a secreted platelet protease converts PF4 to a form with immunoregulatory activity.

Animals↗
PubMed1991

Selective targeting of gene products with the megakaryocyte platelet factor 4 promoter.

We have used the 1.1 kilobases of the 5' upstream region of the platelet factor four (PF4) gene coupled to the prokaryotic beta-galactosidase gene to generate two lines of transgenic mice that express this construct. Studies of blood, bone marrow, spleen, and thymus reveal that platelets are the only circulating blood cells and megakaryocytes are the only hematopoietic precursor cells that possess the prokaryotic enzyme. The lack of transgene expression in brain, heart, intestine, kidney, liver, lung, and skeletal muscle was established by in situ staining of tissue sections as well as kinetic assay of tissue homogenates. These data suggest that this domain of the PF4 promoter contains most, if not all, of the tissue-specific region of the gene. Unexpectedly, the adrenal gland exhibits approximately 2% of the levels of beta-galactosidase possessed by megakaryocytes and the distribution of the prokaryotic enzyme corresponds to the location of mineralocorticoid-secreting cells. This result implies that either the PF4 gene is transcribed at low levels in specialized adrenal cells or that these specialized endocrine cells possess trans-acting factors similar to those that control the megakaryocyte promoter. The selective high-level expression of transgenes linked to the PF4 promoter should allow us to augment or suppress the in vivo levels of critical components in megakaryocytes and platelets and subsequently ascertain the effects of these modifications.

Animals↗
PubMed1993

Platelet factor 4 binds to interleukin 8 receptors and activates neutrophils when its N terminus is modified with Glu-Leu-Arg.

Amino acid deletion and mutagenesis experiments have indicated that the sequences Glu-Leu-Arg (ELR) preceding the first cysteine at the N terminus of interleukin 8 (IL-8) is required for receptor binding and neutrophil activation. Platelet factor 4 (PF4) is structurally related to IL-8 (35% sequence identity) but lacks the N-terminal ELR sequence and comparable effects on neutrophils. We introduced the ELR sequence at the N terminus of PF4 and found that the modified protein was a potent neutrophil activator and attractant. On the other hand, when the ELR sequence was introduced into the corresponding positions of two other proteins related to IL-8, gamma-interferon-inducible protein IP10 and monocyte chemoattractant protein 1, neither of them acquired neutrophil-activating properties, indicating that besides ELR additional structural determinants of IL-8 and PF4 are important for binding to IL-8 receptors. The conservation of these binding determinants suggests that PF4 may have evolved from a neutrophil activating protein.

Amino Acid Sequence↗
PubMed2000

Investigation of a platelet factor 4 polymorphism on the immune response in patients with heparin-induced thrombocytopenia.

A small fraction of patients who receive heparin develop heparin-induced thrombocytopenia (HIT) and, of these patients, a still smaller proportion develop associated thrombotic complications. Heparin-induced thrombocytopenia is caused by the formation of antibodies that bind to specific complexes of platelet factor 4 (PF4) and heparin. However, it remains uncertain why certain patients form these antibodies and develop HIT or why certain patients have thrombotic events. In this report we describe studies on individuals with and without HIT to determined if a potential PF4 polymorphism could explain differences in susceptibility to HIT. In the 10 control individuals and the 10 patients we studied, we did not find a difference in the PF4 sequences. Genetic difference in the PF4 antigenic target does not explain the occurrence of HIT in susceptible patients.

Heparin↗
PubMed1992

Production of novel monoclonal antibodies against rabbit platelet factor four.

Ten hybridomas producing monoclonal antibodies (Mabs) against rabbit platelet factor 4 (PF4) were obtained from the fusion of splenocytes from mice immunized with purified rabbit PF4 and NSO mouse myeloma cells. When the reactivities of these monoclonal antibodies were determined by enzyme-linked immunosorbent assay and immunoblotting with human and rabbit PF4, they showed a high degree of specificity. Only one Mab recognized an epitope common to the human and rabbit molecules, the other nine reacted only with the rabbit protein. All the antibodies recognized, in crude platelet lysates, a band that comigrates with the purified PF4 protein. None of these antibodies cross-reacted with major rabbit or human platelet-poor plasma proteins. The significance of the Mabs in immunological and physiological studies is discussed.

Animals↗
PubMed1992

Alleviation of immunosuppression in vitro by recombinant platelet factor 4.

To elucidate the mechanism by which platelet factor 4 (PF4), a secreted platelet protein, and its C-terminal peptides alleviate suppression of the antibody response in vivo, their immunoregulatory activity was studied in vitro, using cultured spleen cells from BALB/c mice primed with sheep red blood cells (SRBC). When addition of 48 h cultured concanavalin A (Con A) blasts at 5 x 10(5)/ml significantly suppressed the anti-SRBC plaque-forming cell response, suppression was alleviated in 25 of 29 experiments by 0.2 micrograms/ml recombinant (r)PF4 (6.4 nM if rPF4 is a tetramer). The effect of Con A blasts was abolished by cimetidine, a histamine type 2 (H2) antagonist. Dimaprit, an H2 agonist, at 1-2 x 10(-4) M, or splenic T cells that had been incubated for 1 h with dimaprit and washed, also caused significant suppression that was alleviated by 0.2 micrograms/ml rPF4 (n = 8), and by 0.02 micrograms/ml in six of these tests. The C-terminal 13 amino acid peptide of PF4 was active at 0.02-0.2 micrograms/ml (0.01-0.11 microM), but peptides from the middle or N-terminal end of the molecule, or IL-8, which shares structural homology with PF4, were inactive. IL-1 and IL-2 raised control responses without affecting suppression or its alleviation by rPF4. Neutralizing antibody to transforming growth factor beta 1 (TGF-beta 1) did not affect Con A blast-induced suppression and suppression induced by exogenous TGF-beta 1 (0.5 ng/ml) was not counteracted by rPF4. Blocking prostaglandin production with 0.2 or 2 microM indomethacin did not affect suppression significantly but reduced rPF4 activity; prostaglandin D2 restored the effect of rPF4.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Citrate anticoagulation abolishes degranulation of polymorphonuclear cells and platelets and reduces oxidative stress during haemodialysis.

BACKGROUND: During haemodialysis (HD), polymorphonuclear cells (PMNs) and platelets are activated and release various granule products, including myeloperoxidase (MPO) and platelet factor 4 (PF4). MPO triggers the generation of reactive oxygen species, leading to irreversible protein, carbohydrate and lipid modification. PF4 probably also contributes to oxidative stress. As previously shown, HD-induced PMN degranulation is almost completely abolished during citrate anticoagulation, most probably due to its calcium chelation ability. METHODS: In the present study, apart from HD-induced PMN and platelet degranulation, oxidative stress was analysed during three modes of anticoagulation. Heparin, dalteparin and citrate (HDhep, HDdal and HDcit) were compared in a randomized, crossover fashion in eight chronic HD patients. Multiple blood samples were taken during the third HD session of each modality, from both the afferent and efferent line. Besides the degranulation markers MPO and PF4, various markers of oxidative stress were measured, including oxidized low-density lipoprotein (ox-LDL), malondialdehyde (MDA) and carboxymethyllysine (CML). RESULTS: During HDhep and HDdal, marked degranulation was observed shortly after the start of HD. In contrast, during HDcit, PF4 and MPO levels remained unaltered, suggesting no release at all. After 1 week of HDcit, ox-LDL levels were markedly reduced [median 26% (3-65%), P=0.01], if compared with HDhep and HDdal. As regards MDA and CML, no differences were found. CONCLUSIONS: This study shows first, that HD-induced PMN and platelet degranulation are early, most probably calcium-dependent processes and, secondly, that the formation of ox-LDL is clearly dependent on the type of anticoagulant applied.

Adult↗
PubMed1997

Early onset of immunological heparin-induced thrombocytopenia in acute myocardial infarction.

We studied five patients who developed a decrease in platelet count of more than 30000 x 10(6)/l within 24 h of heparin treatment and direct percutaneous transluminal coronary angioplasty and/or intracoronary thrombolytic therapy among 38 consecutive patients with acute myocardial infarction (AMI). Anti-platelet factor 4 (PF4)-heparin complex antibodies were detected in the sera of these five patients, although they had never previously been exposed to heparin. These patients might have had specific antibodies before heparin treatment. PF4 might be released from activated platelets and bind to endogenous heparin-like molecules, and antibodies with cross-reactivity to the PF4-heparin complex may have been generated by the endogenous complex before the first heparin treatment. We conclude that it is worthwhile to check the platelet count and screen for anti-PF4-heparin complex antibody in advance to prevent thrombotic complications due to heparin treatment in patients with AMI.

Acute Disease↗
PubMed1983

Evidence against enhanced platelet activity in sickle cell anaemia.

Although numerous studies have provided indirect evidence for enhanced platelet activity in sickle cell anaemia, little attention has been directed to examination of platelet alpha and dense granule release in the sickling disorders. We simultaneously measured by radioimmunoassay plasma levels of the alpha granule constituents beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) in 43 children with sickle cell anaemia in steady state and 24 patients during severe vaso-occlusive crisis. beta-TG levels during steady state (50 +/- 3.6 ng/ml, mean +/- SEM) were greater (P less than 0.001) than in normal controls (36 +/- 1.6), but there was no additional significant rise during crisis (55 +/- 5.9). PF4 levels were similar (P = 0.12) in both steady state (10 +/- 1.2 ng/ml) and crisis (9.3 +/- 2.3) to those of normal controls (6.0 +/- 0.8). The similarity of beta-TG/PF4 ratios in normal and sickle cell anaemia patients as well as the positive correlation (P less than 0.05) between platelet count and beta-TG and PF4 suggested that an artefactual in vitro platelet activation was responsible for some of the observed increased beta-TG and PF4 levels. Further evidence against enhanced platelet activity in these sickle cell patients included normal intraplatelet content of the dense granule constituent 5-HT and a normal ATP/ADP ratio. From this data we conclude that platelet activation in children with sickle cell anaemia appears minimal.

Adolescent↗
PubMed1984

The significance of fibrinogen derivatives in plasma in human renal failure.

The concentrations in plasma of fibrinogen derivatives fibrinopeptide A (FPA), beta 15-42 antigen and fragment E (FgE) antigen have been determined in patients with renal failure and compared to the concentrations of the platelet release products, beta-thromboglobulin (beta TG) and platelet factor 4 (PF4). In 'partial renal failure' (51Cr-EDTA clearance rate 4-60 ml/min) FPA, beta 15-42 antigen, FgE antigen and beta TG levels were significantly raised above a normal laboratory control group. These levels were further raised in a group of patients whose disease required regular maintenance haemodialysis (51Cr-EDTA clearance rate less than 4 ml/min). PF4 levels were not significantly raised in either group. A statistical analysis of all patient results revealed that FPA, beta 15-42 antigen and FgE antigen levels all correlated with beta TG levels but not with PF4 levels. It is known that beta TG is catabolized by the kidney but PF4 is not and that elevated beta TG levels in renal failure are caused by impaired elimination rather than increased production. These results suggest that the plasma levels of these three fibrinogen derivatives are elevated in renal disease at least in part by decreased elimination rather than by increased thrombin and plasmin activities alone.

Adolescent↗
PubMed2005

Changes in platelet count after cardiac surgery can effectively predict the development of pathogenic heparin-dependent antibodies.

Cardiopulmonary bypass (CPB) induces the release of platelet factor 4 (PF4) and patients are at risk of heparin-induced thrombocytopenia (HIT). This study was aimed to determine whether an abnormal evolution in platelet count (PC) after CPB is predictive of the development of HIT antibodies. Two abnormal PC patterns were defined: pattern P1, characterized by a decrease in PC following previous correction of thrombocytopenia occurring during CPB, and pattern P2, defined as a persistent low PC in the days following CPB. PC was evaluated for 10 d in 305 consecutive patients before and after CPB. Serotonin release assay (SRA) was carried out between days 8 and 10 to detect pathogenic heparin-dependent antibodies. Moreover, antibodies to heparin-PF4 (H-PF4) complexes were assayed by enzyme-linked immunosorbent assay. PC evolution after CPB was normal in 300 patients although antibodies to H-PF4 were frequently present (53.4%). Changes in PC were abnormal in five patients with pattern P1 (n = 4) or P2 (n = 1). As SRA was positive in four of the five cases, the positive predictive value of abnormal PC pattern for pathogenic HIT antibodies was 80%. Careful follow-up of PC after CPB makes it possible to predict with high specificity (99%) for those patients who develop pathogenic HIT antibodies.

Adolescent↗
PubMed2005

Heparin-induced thrombocytopenia antibody and the pathogenesis of thrombotic microangiopathy after stem cell transplantation.

Thrombotic microangiopathy (TMA) that occurs after stem cell transplantation (SCT) is generally regarded as being different from thrombotic thrombocytopenic purpura (TTP), because it is reportedly not associated with deficiency of von Willebrand factor-cleaving protease, whereas this enzyme is deficient in TTP. However, better understanding of the pathogenesis of this condition is still required. Accordingly, we investigated the relationship between TMA occurring after SCT and heparin-induced thrombocytopenia (HIT), a condition related to low-dosed heparin therapy that features thrombocytopenia and generalized thrombotic disorders. Thirty-nine consecutive patients who underwent bone marrow transplantation were divided into a TMA group and a non-microangiopathy group (10 and 29 patients, respectively). Before SCT, the serum platelet factor 4 (PF4) levels of the TMA and non-microangiopathy groups were 0.123 +/- 0.023 and 0.132 +/- 0.025, respectively (p = NS). One week after recovery of the white blood cell count following transplantation, the TMA group (0.2902 +/- 0.0678) had a significantly higher PF4 level than the non-microangiopathy group (0.1548 +/- 0.0312) (p < 0.001, t-test). Thus, PF4 increased after engraftment of the transplanted stem cells in the patients who developed TMA. In patients who developed TMA, there was a significant correlation between the PF4 level and the grade of angiopathy according to the Zeigler grading system (p < 0.01 by linear regression analysis). These results suggest that a HIT antibody produced by donor cells may be involved in the development of TMA after SCT.

Adolescent↗
PubMed1982

Enhanced in vivo platelet activation in diabetes mellitus.

Plasma levels of platelet factor 4 (PF4) determined in 58 apparently healthy subjects were found to increase with age. In 66 insulin dependent diabetics, PF4 plasma levels were increased but unrelated to the age of subject. Mean fibrinopeptide A levels were elevated in the diabetics but not correlated to PF4 levels. Activation of the coagulation system with thrombin generation thus seems to be operative in diabetes, but the enhanced platelet activation also observed in this disease is probably not thrombin mediated. No correlation was found between PF4 plasma concentration and the degree of vascular complication, HbA1C, blood glucose, 24-h urinary glucose, serum cholesterol or serum triglycerides.

Adult↗
PubMed1990

A prospective study of haemostatic parameters in relation to the clinical course of myeloproliferative disorders.

Platelet function and the clinical course of the disease were prospectively investigated in 29 patients with myeloproliferative disorders. Serial determinations (median: 5 investigations per patient within 17 months) of platelet aggregation, plasma and intraplatelet concentrations of beta-thromboglobulin (beta TG) and platelet factor 4 (PF4), and of fibrinopeptide A (FPA) plasma levels were carried out. In the chronic phase of polycythaemia vera, patients with thrombohaemorrhagic complications during the study period had higher platelet count, more severe platelet aggregation defects, and increased plasma levels of beta TG and FPA compared to patients without complications. However, thrombohaemorrhagic complications were not predicted by changes in these parameters in the individual patient during the chronic disease phase. When patients with chronic myelogenous leukaemia entered blast crisis, bleeding complications were related to thrombocytopenia, impaired platelet function and low intraplatelet concentrations of beta TG and PF4. Cytoreduction by chemotherapy in the chronic phase of CML did not alter beta TG and PF4 plasma levels, whereas treatment of polycythaemia rubra vera by venesection favourably influenced platelet alpha-granule secretion and increased intraplatelet concentrations of beta TG and PF4.

Adult↗
PubMed1976

Subcellular localization of the heparin-neutralizing factor in blood platelets.

1. The distribution of the heparin-neutralizing factor (platelet factor 4, PF4) in subcellular organelles of blood platelets of rabbits and man was investigated. 2. In both species the organelles storing 5-hydroxytryptamine (5-HT storage organelles) contained only trivial amounts of PF4. 3. In contrast, the content of PF4 was highest in the subcellular fractions rich in alpha-granules. 4. In conclusion, PF4 is probably localized in the alpha-granules and therefore the platelets contain at least two types of organelles (5-HT organelles and alpha-granules) capable of releasing their contents in response to the same stimuli, such as exposure to collagen, thrombin, etc.

Animals↗
PubMed2005

Beta thromboglobulin and platelet factor 4 in bronchoalveolar lavage fluid of patients with systemic sclerosis.

OBJECTIVE: To evaluate concentrations of the platelet activation markers beta thromboglobulin (BTG) and platelet factor 4 (PF4) in bronchoalveolar lavage fluid (BALF) from patients with systemic sclerosis with and without scleroderma interstitial lung disease (SLD). METHODS: BTG and PF-4 were measured by enzyme immunoassay in BALF from 37 patients with systemic sclerosis. Controls were 10 healthy subjects. BALF was collected during routine bronchoscopy from the right middle lobe. SLD was diagnosed by high resolution computed tomography of the lungs. RESULTS: BTG was detected in 11 of the patients with systemic sclerosis (29.7%) and PF4 was found in eight (21.6%). Mean (SD) concentrations of BTG and PF4 in BALF from patients with detectable levels of these platelet activation markers were 106.9 (69.8) and 35.2 (17.4) IU/ml, respectively. The BTG:PF4 ratio was more than 2:1, indicating in vivo release. Both markers were found exclusively in patients with SLD. SLD patients with detectable platelet activation markers had a significantly shorter disease duration than those with undetectable BTG/PF4. CONCLUSIONS: The study provides evidence that activation of blood platelets takes place within the lungs of patients with SLD and may contribute to the development of lung fibrosis.

Adult↗