Platelet crossmatching for kidney transplants by flow cytometry

Although flow cytometry crossmatching is now performed by many kidney transplant centers, it yields a high false-positive rate, as evidenced in the present series by a 71% one-month success rate despite a positive crossmatch. In an attempt to reduce false-positive reactions while retaining the sensitivity of the flow cytometer, platelets were tested as targets. Whereas flow cytometry with T cells was not correlated with one-month failure rates, retrospective platelet crossmatching by flow cytometry showed that kidney failure within one month occurred in 53% of 19 patients with a positive platelet crossmatch compared with 15% of 48 patients with a negative platelet crossmatch. (P less than 0.002). Statistical significance in one-month outcome was also obtained when only first transplant patients were analyzed (P less than 0.04). The present results suggest that crossmatching with platelet targets may be a simpler way to avoid early primary nonfunction while minimizing false-positive reactions.

Differentiation between Bernard-Soulier syndrome and immune thrombocytopenia by immunostaining of peripheral blood

Peripheral blood smears from seven patients with Bernard-Soulier syndrome were examined by an immunocytochemical staining procedure using a monoclonal antibody specific for platelet glycoprotein Ib. No platelet staining was observed except for very slight staining of the large sized platelets from one of the patients. Application of the assay to blood smears from 12 patients with immune thrombocytopenia showed that their peripheral platelets stained normally, so the assay can be used to differentiate between immune thrombocytopenia and Bernard-Soulier syndrome and to confirm a diagnosis of the syndrome.

Arterial thrombosis associated with immune thrombocytopenia: presence of a platelet aggregating IgG synergistic with thrombin and adrenalin

We report the case of a 50-year-old lady who presented with arterial thrombosis in the setting of thrombocytopenia. Investigations confirmed the diagnosis of idiopathic thrombocytopenic purpura. A spontaneous platelet aggregating factor (SPAF) was isolated from the immunoglobulin fraction of the patient's plasma. The isolated IgG irreversibly aggregated platelet-rich plasma and washed platelets, an effect abolished by pretreating the platelets with aspirin. The activity of the IgG was greatly enhanced by subaggregatory concentrations of thrombin and adrenalin and was localized to the F(ab')2 of the molecule. Plasmapheresis in combination with anti-platelet therapy resulted in an increase in the patient's platelet count, reduced platelet aggregating activity of plasma and significant clinical improvement. We suggest that the presence of this platelet aggregating IgG contributed to the development of thrombosis in our patient and postulate that a similar factor may explain the paradox of thrombosis observed in a select group of thrombocytopenic patients.

Platelets as inhibitory cells in neutrophil-mediated cytolysis

Neutrophilic polymorphonuclear leukocytes (PMNs), triggered by opsonized zymosan (OPZ), lysed chicken red blood cells as measured by a chromium 51 release method. The lysis was prevented by scavengers of hypochlorous acid. When platelets were added to the cytolytic system, a dose-dependent inhibition of the lysis was observed. Moreover, platelets lowered the HOCl recovery from OPZ-triggered PMNs. A positive linear relationship was found between the extent of the lysis mediated by and the amount of HOCl recovered from PMNs. Finally, both the inhibition of the lysis and the reduction of the HOCl recovery induced by platelets were prevented by pulsing platelets with carmustine (BCNU) to block their glutathione cycle. These results suggest that platelets act by consuming via their glutathione cycle significant amounts of PMN-derived hydrogen peroxide, with a consequent impairment of the PMN HOCl production and, in turn, lytic efficiency. Consistent with such a conclusion, platelets were found to consume PMN-derived H2O2 via a BCNU-inhibitable process. Further, the platelet inhibitory activity could be abolished by the addition of an appropriate extra-flux of enzymatically generated H2O2. No evidence for a platelet-induced inhibition of OPZ-PMN interaction, PMN myeloperoxidase release, and H2O2 production was obtained. The present study provides direct evidence for a platelet-dependent mechanism capable of controlling the PMN production of highly reactive oxidants and, in turn, the PMN cytolytic activity.

IgA nephritis: a review of the pathogenetic mechanisms and the rationale for therapy

Various pathogenetic mechanisms are involved in IgA nephritis: immunological; platelet, coagulation and vascular injury; mesangial cell proliferation and contractility; hypertension; glomerular hyperperfusion and tubulo-interstitial injury. It is now possible to identify the subgroup of patients with IgA nephritis who have adverse prognostic features and may develop progressive glomerular scarring with renal failure. These features are proteinuria greater than 1 gm/day, non-selective proteinuria, glomerulosclerosis, hypertension, crescents and medial hyperplasia of blood vessels on renal biopsy. Controlled trials involving cyclophosphamide, anti-platelet agent (dipyridamole) and low dose warfarin; prednisolone; angiotensin converting enzyme inhibitors and eicosapentanoic acid (fish oil) appear promising. Currently, patients with bad prognostic indices in the Department are offered entry into an ongoing controlled trial of dipyridamole and low dose (anti-thrombotic dose) warfarin. Those patients with nephrotic syndrome especially with selective proteinuria are treated with a course of prednisolone and failing that, cyclophosphamide. It is important to maintain adequate blood pressure control among hypertensive patients as uncontrolled hypertension can lead to accelerated renal failure. With the onset of even mild renal impairment, dietary protein restriction should be recommended as this will help to decrease the rate of renal deterioration due to glomerular hyperfusion.

Long-term danazol therapy in autoimmune thrombocytopenia: unmaintained remission and age-dependent response in women

STUDY OBJECTIVE

To assess the long-term benefit and side effects of danazol therapy, and to delineate factors influencing the responses in patients with autoimmune thrombocytopenia.

DESIGN

Before and after trial.

SETTING

Referral-based hematology clinics and the University of Miami teaching hospitals.

PATIENTS

Data were collected on 96 patients (60 women and 36 men, 45 of whom had had splenectomies) receiving danazol therapy for autoimmune thrombocytopenia and analyzed.

INTERVENTION

Danazol was added to the previous therapy or begun as an initial therapy. Glucocorticoids were tapered gradually.

MEASUREMENTS AND MAIN RESULTS

The overall response rate to danazol was 61.4%. Among responders, the platelet counts (mean +/- SD) before and after danazol treatment were 36 +/- 24 x 10(9)/L and 145 +/- 77 x 10(9)/L, respectively, and the time to response was 2.7 +/- 3 months. Sex, age, and the status of the spleen (absent or present) influenced the responses to danazol. In women, but not in men, response rates improved with advancing age, especially in the nonsplenectomized women. This may be because estrogen levels are high in younger women and low in older women and men. Danazol, when given longer than a year, induced remissions lasting for years even after its discontinuation, but early relapses were frequent when danazol was administered for less than 6 months. Platelet-associated IgG returned to normal range during unmaintained remission.

CONCLUSION

Danazol is best suited for long-term medical management of autoimmune thrombocytopenia. It is well tolerated, and lasting, unmaintained remissions often occur after prolonged danazol administration. Age, sex, and the status of the spleen influence the responses. When danazol therapy is used, glucocorticoids can be substantially reduced in dosage or withdrawn. Danazol is a good alternative to splenectomy in elderly persons, especially in women.

Role of platelets in smooth muscle cell proliferation and migration after vascular injury in rat carotid artery

Intimal lesion formation was investigated in rats made thrombocytopenic by a single i.p. injection of a polyclonal antibody made against rat platelets that reduced circulating platelet counts to less than 1% of normal. The carotid artery was then denuded of endothelium with a 2 French balloon catheter, after which no platelets were found adhering to the exposed subendothelium. In control animals, platelets adhered instantly to the denuded artery. Six hours after denudation mRNA for ornithine decarboxylase, a marker for early G1 events, was found to be elevated in both thrombocytopenic and control arteries. Two days after injury the smooth muscle cell replication rate in thrombocytopenic rats was found to be significantly elevated as compared with that in uninjured carotids (13.7% +/- 8.4% vs. 0.65% +/- 0.23%) but was similar to the replication rate observed in denuded carotid arteries from animals treated with nonimmune IgG. One important difference between these animals was that no intimal thickening was observed in thrombocytopenic animals at day 4, and by day 7 the intimas were still significantly smaller than those from control rats. In a separate group of animals which were thrombocytopenic for the entire experiment, no intimal lesions were observed 7 days after injury by balloon catheter. From these results, we conclude that platelets do not play a role in the initiation of smooth muscle cell proliferation after injury by balloon catheter but may regulate their movement into the intima.

Sequential imaging of post-operative thrombus using the In-111-labelled platelet-specific monoclonal antibody P256

Eleven patients undergoing total hip replacement were studied by radioimmunoscintigraph for development of postoperative thrombus. Images were obtained using the 111In-labelled Fab' fragment of a monoclonal antibody (P256) directed against human platelets. Six patients showed focal accumulation of radioactivity in the lower limbs. Three of these had contrast venograms that were all positive for thrombus. Two of these six patients showed evidence of pulmonary localization of P256-Fab' and this correlated with positive ventilation/perfusion scintigraphy in one of the patients. Sequential imaging with 111In-P256 Fab' not only established a diagnosis of deep venous thrombus but also provided useful information regarding its natural history.

[Association of Basedow's disease and autoimmune thrombopenic purpura. No effect of hyperthyroidism on antiplatelet autoimmunity]

The association between Graves' disease and autoimmune thrombocytopenic purpura is rare and yet more frequent than would be expected from a mere coincidence. The existence of an immunological disorder common to Graves' disease and autoimmune thrombocytopenic purpura and/or a direct responsibility of hyperthyroidism in the genesis of immunological disturbances resulting in autoimmune thrombocytopenic purpura are hypotheses put forward to try and explain why these two pathologies are associated. We report two cases in which the antiplatelet autoimmunity developed independently of the thyroid functional disorder, making it unlikely that hyperthyroidism played a direct role in the occurrence of the immunological disorders responsible for the autoimmune thrombocytopenic purpura. The physiopathology responsible for the Graves' disease-autoimmune thrombocytopenic purpura association remains imperfectly known. The existence of an immunological pathogenetic mechanism underlying both diseases seems to be likely; it probably acts through an antigenic determinant that is common to thyroid cells and platelets.

Post-transfusion purpura and isoimmune neonatal thrombocytopenia in the same family

Post-transfusion purpura and isoimmune neonatal thrombocytopenia are rare and unusual syndromes leading to severe thrombocytopenia. In both disorders the PLA1 platelet antigen is involved in the pathogenesis. A 41-year-old woman with an obstetrical history of isoimmune neonatal thrombocytopenia in two of her children developed post-transfusion purpura following a transfusion of packed red blood cells. Despite the apparent link in these two disorders associated with the PLA1 platelet antigen, this is the first reported case of post-transfusion purpura and isoimmune neonatal thrombocytopenia occurring in the same family.

Immune adherence of nascent hepatitis B surface antigen-antibody complexes in vivo in humans

Upon i.v. injection into humans, pre-formed immune complexes bind complement and adhere to complement receptor type I (CR1, CD35) on erythrocytes (immune adherence). However, in most circumstances antigen and antibody react in the presence of complement; such nascent immune complexes may have properties different from pre-formed immune complexes. To define whether nascent immune complexes would also adhere to erythrocytes in vivo in humans, we studied immune complexes that formed upon i.v. injection of radiolabelled hepatitis B surface antigen (HBsAg) into immunized volunteers (eight subjects with anti-HBsAb levels ranging from undetectable to 50 U/ml.; and three control non-immune individuals). Immune complexes formed immediately in the subjects with detectable levels of specific antibody, and the clearance rate of these immune complexes correlated with the anti-HBsAb level (r = 0.78, P < 0.01). A fraction of the circulating immune complexes bound to erythrocytes in the three individuals with the highest antibody level (8-15% at 10 min). The effect of CR1 number per erythrocytes was analysed in two subjects with similar antibody levels and immune complexes clearance rates: immune adherence was higher in the subject with more CR1 per erythrocytes. The same immune complexes model studied in vitro provided similar results: a fraction of nascent immune complexes bound to human erythrocytes; this immune adherence was observed only when immune complexes formed in the presence of antibody excess, and correlated with CR1 number per erythrocytes (r = 0.99, P < 0.01). Finally, adherence of nascent HBsAg-antibody immune complexes to platelets was demonstrated in rabbits. Although immune adherence involves only a small fraction of nascent immune complexes at any given time, it may be essential for the safe disposal of large nascent immune complexes.

Mechanisms of platelet destruction in immune-mediated thrombocytopenia: in vitro studies with canine platelets exposed to heterologous and isologous antiplatelet antibodies

Normal canine platelets coated with heterologous or isologous antiplatelet antibody were interacted with viable canine neutrophils in vitro. Platelet phagocytosis was assessed by detecting nitroblue tetrazolium (NBT) reduction, measuring uptake of opsonised 51Cr-labelled platelets, and electron microscopy. The NBT reduction and uptake of 51Cr-labelled opsonised platelets were markedly increased. Electron microscopy revealed phagocytosis of antibody-coated platelets and their degradation intracellularly. Exposure of canine platelets to rabbit anti-canine platelet antibody in vitro produced morphological changes in platelets and caused serotonin release. Serotonin was not released in the absence of antiplatelet antibody or in the presence of normal rabbit gamma-globulin. Morphological changes in the platelets included disappearance of alpha and dense granules and exaggeration of the open canalicular system. These observations indicate that circulating platelets may be vulnerable to an antiplatelet antibody and that antibody-mediated phagocytosis of platelets is an important mechanism in the pathogenesis of immune-mediated thrombocytopenia.

A simple, rapid method for screening hybridomas producing monoclonal antibodies to platelet proteins

Several parameters influence the outcome of somatic cell fusions based on the Köhler and Milstein technology, and a number of steps are of critical importance, including the screening strategy. The procedure chosen, appropriate for the type of antibody required, should be rapid and sensitive, in order to clone the relevant hybrids as quickly as possible. A simple and quick dot blot-based method is reported, suitable for screening hybridoma culture supernatants in order to identify clones producing monoclonal antibodies to platelet constituents.

Monoclonal antibodies and thromboembolism

For many years intensive efforts to reliably image thrombi by radionuclide techniques have been unrewarding. Recently, however, monoclonal antibodies to platelet cell-surface antigens and to fibrin polymer have emerged as potent thrombus imaging agents in experimental animals. In Britain antiplatelet antibody has been successful in clinical trials, as has antifibrin in the United States. It is to be hoped that radiolabeled antibody technology will evolve to the point where it can detect thrombi anywhere, including the lungs and brain. The relative efficacy of radionuclide thrombus detection and Doppler ultrasonography is currently undefined.

[The effect of blood platelet freezing on their antigen activity]

The authors investigated the effect of freezing of platelets after addition of various cryoprotective substances (glycerol, dimethyl sulphoxide and hydroxyethyl starch) on the preservation of some antigenic properties of these blood cells. It was revealed that during freezing of platelets in 5% glycerol and 4% hydroxyethyl starch no change of the specific antigen Kob and of HLA antigens occurred. Freezing in dimethylsulphoxide, however, weakened the activity of some antigens; usually this applied to antigen Kob, in HLA antigens it was rather an exception. From the results ensues, however, that in the transfusion practice it is important to foresee even in transfusions of cryopreserved platelets possible alloimmunization.

Human hyperimmune globulin protects against the cytotoxic action of staphylococcal alpha-toxin in vitro and in vivo

Alpha-toxin, the major cytolysin of Staphylococcus aureus, preferentially attacks human platelets and cultured monocytes, thereby promoting coagulation and the release of interleukin-1 and tumor necrosis factor. Titers of naturally occurring antibodies in human blood are not high enough to substantially inhibit these pathological reactions. In the present study, F(ab')2 fragment preparations from hyperimmune globulin obtained from immunized volunteers were tested for their capacity to inhibit the cytotoxic action of alpha-toxin in vitro and in vivo. These antibody preparations exhibited neutralizing anti-alpha-toxin titers of 80 to 120 IU/ml, whereas titers in commercial immunoglobulin preparations were 1 to 4 IU/ml. In vitro, the presence of 2 to 4 mg of hyperimmune globulin per ml protected human platelets against the action of 1 to 2 micrograms of alpha-toxin per ml. Similarly, these antibodies fully protected human monocytes against the ATP-depleting and cytokine-liberating effects of 0.1 to 1 microgram of alpha-toxin per ml. Intravenous application of 0.5 mg (85 to 120 micrograms/kg of body weight) of alpha-toxin in cynomolgus monkeys elicited acute pathophysiological reactions which were heralded by a selective drop in blood platelet counts. Toxin doses of 1 to 2 mg (170 to 425 micrograms/kg) had a rapid lethal effect, the animals presenting with signs of cardiovascular collapse and pulmonary edema. Prior intravenous application of 4 ml of hyperimmune globulins per kg inhibited the systemic toxic and lethal effects of 1 mg (200 micrograms/kg) of alpha-toxin. In contrast, normal human immunoglobulins exhibited no substantial protective efficacy in vitro and only marginal effects in vivo. It is concluded that high-titered anti-alpha-toxin antibodies effectively protect against the cytotoxic actions of alpha-toxin.

Effect of aspirin on heparin-induced thrombocytopenia (HIT) in a patient requiring hemodialysis

The present report describes the management of a 75-year-old uremic patient with delayed-onset heparin-induced thrombocytopenia and clot formation in extracorporeal circulation. The test for serum heparin-dependent platelet aggregation factor was positive and the serum platelet binding IgG (PBIgG) became elevated after the onset of heparin-induced thrombocytopenia. He required continuous exposure to heparin for hemodialysis. One gram of aspirin daily was begun to prevent clot formation in the circuit. Hemodialysis with full heparinization was achieved with no clot formation in the circuit. After aspirin ingestion, the increased level of patient's PBIgG in the presence of heparin and thrombocytopenia were restored to normal. Inhibition of platelet aggregation with aspirin allowed uneventful dialysis in a patient with heparin-induced thrombocytopenia.

Thrombocytopenia associated with heparin-coated catheters in patients with heparin-associated antiplatelet antibodies

Thrombocytopenia was associated with the presence of heparin-coated pulmonary artery catheters in 12 patients with heparin-associated antiplatelet antibodies. The thrombocytopenia persisted so long as the heparin-coated catheters were in place, even when all other sources of heparin were discontinued. The high morbidity and mortality associated with heparin-induced thrombocytopenia mandates that heparin administration cease and that all heparin-coated catheters be removed from patients with heparin-associated antiplatelet antibodies.