Human platelet antigens - 2013.

To date, 33 human platelet alloantigens (HPAs) have been identified on six functionally important platelet glycoprotein (GP) complexes and have been implicated in alloimmune platelet disorders including foetal and neonatal alloimmune thrombocytopenia (FNAIT), posttransfusion purpura (PTP) and multitransfusion platelet refractoriness (MPR). The greatest number of recognized HPA (20 of 33) resides on the GPIIb/IIIa complex, which serves as the receptor for ligands important in mediating haemostasis and inflammation. These include HPA-1a, the most commonly implicated HPA in FNAIT and PTP in Caucasian populations. Other platelet GP complexes, GPIb/V/IX, GPIa/IIa and CD109, express the remaining 13 HPAs. Of the recognized HPAs, 12 occur as six serologically and genetically defined biallelic 'systems' where the -a form designates the higher frequency allele and the -b form, the lower. Twenty-one other HPAs are low-frequency or rare antigens for which postulated higher frequency -a alleles have not yet been identified as antibody specificities. In addition to the HPA markers, platelets also express ABO and human leucocyte antigen (HLA) antigens; antibodies directed at the former are occasionally important in FNAIT, and to the latter, in MPR.

Report on the 14th International Society of Blood Transfusion Platelet Immunology Workshop.

BACKGROUND AND OBJECTIVES: The aims of the 14th ISBT Platelet Immunology Workshop were to evaluate in-house methods for detection of antibodies to human platelet antigens, to compare the sensitivity and specificity of antibody detection using a panel of monoclonal antibodies and to evaluate genotyping methods and establish procedures for drug-dependent antibody detection. MATERIALS AND METHODS: Forty-two laboratories from 23 countries participated. Samples and reagents provided for the five different exercises. RESULTS: The ability of participating laboratories to correctly identify the HPA antibody specificity in the nine samples ranged from 20% to 97%. The greatest difficulty was observed with samples that contained antibodies against HPA-3b and GPIV. The significant differences in optical density values by monoclonal antibody of immobilization of platelet antigens (MAIPA) assay were observed when testing the same platelet-specific antibodies. HPA genotyping of DNA with novel mutations did not significantly affect the results. The overall average discrepancy rate was 2·15% for genotyping of 10 DNA samples from well-characterized Epstein­Barr virus transformed cell lines. For detection of drug-dependent antibodies, excellent results for specificity and sensitivity were obtained by the laboratories using the MAIPA and flow cytometry. CONCLUSIONS: Most laboratories were able to identify the majority of HPA antibodies; however, significant disparities were observed in proficiency testing. MAIPA assay sensitivity is influenced by the monoclonal antibody clone used. DNA with new mutations and EBV cell lines are valuable samples to ensure accurate genotyping. A sensitive and specific drug-dependent antibody assay performed well in the hands of participants.

Detection and identification of platelet antibodies and antigens in the clinical laboratory.

As a result of the unique functional properties of platelets, more-robust methods were required for detection of antibodies raised against them. Immunofluorescence detection by flow cytometry, solid-phase red cell adherence, and antigen capture ELISAs are some of the current tests that have been developed to meet the challenges of platelet antibody detection and identification and antigen phenotyping. Recently developed protein liquid bead arrays are becoming the next-generation platelet antibody tests. Fueled by development of PCR and determination of the molecular basis of the PlA1 human platelet antigen (HPA), serologic platelet typing has now been replaced by genotyping of DNA. Allele-specific PCR, melting curve analysis, and 5'-nuclease assays are now evolving into more high-throughput molecular tests. Laboratory testing for the diagnosis of immune platelet disorders has advanced considerably from its humble beginnings.

A patient with oxaliplatin immune-induced syndrome (OIIS) who also developed leucovorin and palonosetron-associated thrombocytopenia.

OBJECTIVES: We report a case of an 83 year old man who developed oxaliplatin immune-induced syndrome (OIIS) after his 19th cycle of FOLFOX (5FU, leucovorin, oxaliplatin). When oxaliplatin was omitted from his next cycle of chemotherapy he continues to show signs of drug-induced immune thrombocytopenia (DITP) and was found to have drug-dependent, platelet-reactive antibodies (DDPA) to leucovorin and palonosetron as well as oxaliplatin. METHODS: The patient was admitted for monitoring but required no transfusions and thrombocytopenia resolved without treatment during his first admission. Drug-dependent antibody testing was performed on his blood by the Blood Center of Wisconsin (Diagnostic Laboratories; Milwaukee, WI). RESULTS: No RBC or platelet IgG or IgM antibodies were detected in the absence of any drugs, but upon addition of palonosetron, leucovorin, or oxaliplatin, the tests became strongly positive for anti-RBC IgG and anti-platelet IgG antibodies. DISCUSSION: Repeated administration of oxaliplatin can result in drug-induced immune thrombocytopenia (DITP) or autoimmune hemolytic anemia (AIHA). This phenomenon has recently been termed OIIS and may additionally include Evan's syndrome or thrombotic microangiopathy (TMA). Here we describe a patient who developed OIIS with drug-dependent, platelet-reactive antibodies (DDPA) to leucovorin and palonosetron. To our knowledge, these two drugs have never been described in the literature as a cause of DDPA. We suggest that OIIS in addition to oxaliplatin-induced thrombocytopenia may be associated with the development of DDPAs to other drugs causing clinically significant thrombocytopenia which is important to recognize and manage with discontinuation of provoking agents.

Delayed thrombocytopenia after treatment with abciximab: a distinct clinical entity associated with the immune response to the drug.

BACKGROUND: Acute thrombocytopenia is a recognized side-effect of treatment with the fibrinogen receptor antagonist, abciximab, a chimeric (human/mouse) Fab fragment. The etiology of this complication is not fully understood. Generally, abciximab-induced thrombocytopenia occurs within a few hours of starting treatment with the drug. We have characterized a group of 13 patients who first developed thrombocytopenia 3-6 days after abciximab was discontinued. OBJECTIVE: To characterize clinical and serological aspects of this newly recognized clinical entity. PATIENTS AND METHODS: Clinical information was obtained from attending physicians and review of hospital records. Antibodies reactive with abciximab-coated platelets were characterized by flow cytometry. RESULTS: In each patient, IgG and/or IgM antibodies reactive with abciximab-coated platelets were identified. These antibodies could be distinguished from similar antibodies present in many normal persons by two criteria-they were relatively resistant to inhibition by normal Fab fragments, and they reacted preferentially with platelets coated with 7E3, the murine monoclonal antibody from which peptide sequences in abciximab are derived. Antibodies with these characteristics were not found in pretreatment serum from three of the thrombocytopenic patients or in patients given abciximab who did not develop thrombocytopenia. CONCLUSIONS: 'Delayed thrombocytopenia' after treatment with abciximab is caused by antibodies produced in response to the drug. These antibodies may be specific for murine peptide sequences in abciximab but could recognize other target epitopes on abciximab-coated platelets. Physicians administering abciximab should be aware of this potential complication of treatment, which usually occurs after discharge from hospital.

Refractory immune hemolytic anemia with a high thermal amplitude, low affinity IgG anti-Pra cold autoantibody.

A 54 y.o. woman presented with acute Coombs-negative hemolytic anemia at an outside hospital where she received 25 RBC transfusions and did not respond to prednisone or splenectomy. On transfer to our hospital, routine DAT and IAT were weakly positive, occasionally negative. When a modified "cold" antiglobulin test was employed, the result was strongly positive for IgG, weakly positive for C3d. Cold agglutinin titer was 32, and the Donath-Landsteiner test was negative. The autoantibody exhibited Pra specificity. The patient failed IV-IgG, high dose IV pulse steroids and cyclophosphamide, and continued to require daily transfusions. She responded 21 days after receiving daily plasma exchange (x3), with pulse cyclophosphamide on the third day, followed by escalating daily oral cyclophosphamide.

Posterior inferior junction line and left pleuroesophageal stripe: their association with emphysema.

In an effort to define the posterior inferior junction line (PIJL) and its clinical associations more precisely, 64 posteroanterior radiographs demonstrating the PIJL or left pleuroesophageal stripe (LPES) were analyzed for the presence of emphysema, kyphosis, air-filled esophagus, and/or tortuous aorta. Pursuant to the possible association of a PIJL or LPES with an air-filled esophagus, posteroanterior radiographs of 66 patients with achalasia were evaluated for the presence of a PIJL or LPES. To determine the components of the PIJL or LPES, 50 randomly selected computed tomographs (CT) of the chest were reviewed. Finally, 118 posteroanterior radiographs of patients with emphysema were analyzed for the presence of a PIJL and/or LPES to determine the sensitivity of the line/stripe for emphysema. The finding of a PIJL and/or LPES had a combined sensitivity of 23% for emphysema. Although certain other anatomic constructs lead to the presence of a line or stripe, emphysema is the most commonly associated clinical entity with a positive predictive value of 65.8%. The line and/or stripe is formed by interfaces between lung/lung, lung/esophagus, or both at different levels.

Drug-induced immune thrombocytopenia: pathogenesis, diagnosis, and management.

Drug-induced immune thrombocytopenia (DITP) can be triggered by a wide range of medications. Although many cases of DITP are mild, some are characterized by life-threatening bleeding symptoms. The pathogenesis of DITP is complex, in that at least six different mechanisms have been proposed by which drug-induced antibodies can promote platelet destruction. It is possible in many cases to identify antibodies that react with platelets in the presence of the sensitizing drug, but the required testing is technically demanding and not widely available. Therefore, a decision on whether to discontinue an implicated medication in a patient suspected of having DITP must be made on clinical grounds. An algorithm is available that can be helpful in assessing the likelihood that a particular drug caused thrombocytopenia, but the most important aspects of patient management are a high index of suspicion and a careful history of drug exposure in an individual who presents with acute, often severe thrombocytopenia of unknown etiology. How drugs induce platelet-reactive antibodies and how, once formed, the antibodies cause platelet destruction following exposure to the drug is poorly understood. Further studies to address these issues and characterize more completely the range of drugs and drug metabolites that can cause DITP are needed.

Prospective evaluation of a new platelet glycoprotein (GP)-specific assay (PakAuto) in the diagnosis of autoimmune thrombocytopenia (AITP).

Assays measuring platelet-associated immunoglobulin G (PAIgG), while highly sensitive, lack specificity in diagnosing autoimmune thrombocytopenia (AITP). We prospectively evaluated a new commercially available glycoprotein (GP)-specific assay, the PakAuto (GTI, Brookfield, WI), for its clinical usefulness in distinguishing immune from nonimmune thrombocytopenia (TP), in 216 patients with autoimmune TP (both primary "idiopathic" and "secondary") and 46 patients with TP due to other causes. This assay is designed to detect both platelet-associated (direct assay) and plasma (indirect assay) antiplatelet antibodies specific for GPs IIb/IIIa, Ib/IX, and Ia/IIa. The mean platelet counts of the immune (79 +/- 7 x 10(9)/L) and nonimmune groups (78 +/- 7 x 10(9)/L), were similar (P=0.95). The direct assay was positive in 114/216 patients with AITP (53%), and 13/46 with nonimmune TP (28%). Among the AITP group, the majority (61%) of patients with positive test results had autoantibodies reactive against all three GP targets. The sensitivity, specificity, positive, and negative predictive values for the direct PakAuto were 53%, 72%, 90%, and 24%, respectively, comparable to previously published experience of GP-specific assays. However, in some cases of TP due to nonimmune cause, the PakAuto was highly specific. Only 3 of 22 patients with gestational and 1 of 8 with familial/congenital TP had a positive direct assay, indicating that the test may be particularly useful for excluding an immune etiology for TP in certain patient subgroups.

Incidence of the Nak(a)-negative platelet phenotype in African Americans is similar to that of Asians.

BACKGROUND: About 5 to 10 percent of Asians have platelets that lack the major membrane glycoprotein (GP) IV (CD36, GPIIIb) that carries the isoantigen Naka. The GPIV-negative platelet phenotype is extremely rare among whites, but its frequency in persons of African ancestry has not yet been determined. Isoimmunization against GPIV can occur in GPIV-negative persons and can lead to platelet transfusion refractoriness. Therefore, the expression of GPIV on platelets from unrelated African Americans was studied. STUDY DESIGN AND METHODS: Platelets were obtained from 250 African American and 280 white blood donors. Flow cytometry was used to determine the ability of these platelets to bind a monoclonal antibody that reacted with GPIV. Platelets that failed to react with this probe were tested with other GPIV-specific monoclonal antibodies and with anti-Naka, an isoantibody that recognizes an epitope on GPIV. RESULTS: Platelets from 6 of the 250 African American donors (2.4%) lacked GPIV and failed to bind anti-Naka, whereas platelets from all of the white donors were GPIV positive (p>0.05). No platelet-reactive antibodies were identified in the serum of the GPIV-negative donors. CONCLUSION: The frequency of the GPIV-negative platelet phenotype in African Americans is comparable to that in Asians and much greater than that in whites. Studies are needed to determine the frequency with which African Americans become isoimmunized to GPIV by transfusions and the possible contribution of this isoimmunization to platelet transfusion refractoriness in this population.

A latex particle assay for platelet-associated IgG.

A modified, sensitive, solid-phase assay for platelet-associated IgG is reported. Direct comparisons were made between a 125I monoclonal radioimmunoassay (RIA) and the polyclonal antibody latex particle assay. In 209 simultaneous comparisons with the RIA, the sensitivity of the latex test was 91 percent, specificity was 100 percent, and overall efficiency was 97 percent. Commencing with platelet-rich plasma, the direct latex particle test for platelet-bound IgG requires 45 minutes; 90 minutes are required to crossmatch one patient with 12 donors. The advantages of the latex assay are absence of radioactivity, stability of reagents, economy, speed, specificity, and sensitivity.

Life-threatening, antiglobulin test-negative, acute autoimmune hemolytic anemia due to a non-complement-activating IgG1 kappa cold antibody with Pra specificity.

A 21-year-old man with fulminant cold autoantibody hemolytic anemia (CAHA) was hospitalized with hemoglobinemia, hemoglobinuria, hemoglobin concentration of 3.3 gm per dL, a negative direct antiglobulin test (DAT) with polyspecific and anti-C3d reagents, a negative Donath-Landsteiner test, and a cold agglutinin titer of 80. He failed to respond to corticosteroids, multiple plasma exchanges, and cyclophosphamide; he required 54 transfusions in 10 days to maintain a hemoglobin concentration of 6.0 to 10.0 g per dL. He improved dramatically after a splenectomy was performed. The wide-thermal-amplitude cold agglutinin proved to be an IgG1 kappa antibody with Pra specificity. The patient's serum exhibited normal complement activation. When the DAT was carried out at 0 to 4 degrees C, the result was strongly positive for IgG; the indirect antiglobulin test at 0 to 4 degrees C was positive with the patient's serum diluted 1 in 640. Within 6 months, he was in complete remission and receiving no therapy. As compared with eight patients with CAHA that was exclusively IgG-mediated, this patient is remarkable for his requirement for many transfusions and for DATs that were consistently negative for C3d.

An antibody from a patient with ranitidine-induced thrombocytopenia recognizes a site on glycoprotein IX that is a favored target for drug-induced antibodies.

Although thrombocytopenia associated with the use of histamine H2 receptor (H2R) antagonists has been described, a drug-dependent, platelet-reactive antibody has not previously been identified in such cases. We studied serum from a patient who developed acute, severe thrombocytopenia after exposure to the H2 receptor antagonist, ranitidine, and identified an antibody that reacted with normal platelets in the presence of this drug at pharmacologic concentrations. In flow cytometric and immunoprecipitation studies, the antibody was shown to be specific for the glycoprotein Ib/IX complex (GPIb/IX). From the pattern of monoclonal antibody (MoAb) inhibition and the reactions of antibody with Chinese hamster ovary (CHO) cells transfected with GPIX and GPIbbeta, we found that the patient's antibody is specific for an epitope on GPIX close to, or identical with a site recognized by the MoAb SZ1 that is a common target for antibodies induced by quinine and quinidine, drugs structurally unrelated to ranitidine. These findings provide evidence that immune thrombocytopenia can be caused by sensitivity to an H2 R antagonist and suggest that the SZ1 binding site on GPIX may be a common target for drug-induced antibodies. Further studies of the epitope for which SZ1 is specific may provide clues to the mechanism(s) by which drugs promote tight binding of antibody to a membrane glycoprotein and cause platelet destruction in patients with drug sensitivity.

Immunoglobulin isotype identification in red cell antibodies using flow cytometry.

BACKGROUND: Identifying the isotype of an immunoglobulin (IgM vs. IgG) detected in a patient sample is especially important in anticipating the risk of hemolytic disease of the newborn. Currently, 2-mercaptoethanol (2-ME) treatment of a sample is used in the authors' laboratory to degrade IgM, and this is followed by retesting. This method has multiple drawbacks. The purpose of this study was to develop a flow cytometry (FC) assay that would replace the 2-ME treatment protocol (2-ME treatment). STUDY DESIGN AND METHODS: A preliminary FC assay was developed, modified, and refined through the use of stock antibodies. Then, 10 samples containing antibodies were tested in parallel by the FC assay and 2-ME treatment. RESULTS: When a 10-unit mean channel fluorescence change was used as an index of a positive result, the FC assay detected all isotypes identified by 2-ME treatment. The FC assay was also able to identify mixtures of isotypes. One antibody that had not reacted in conventional agglutination testing was detected by the FC assay. The amount of fluorescence and the agglutinating strength of the antibody did not parallel each other. In one case, this discrepancy may have reflected an antibody that was primarily IgA. CONCLUSIONS: The FC assay appears to be as accurate as 2-ME treatment in differentiating IgG from IgM. The FC assay produces a positive endpoint for both isotypes, will identify IgA, requires less sample, and has no odor.

Low retention of white cell fragments by polyester fiber white cell-reduction platelet filters.

BACKGROUND: There is intense interest in the potential of current white cell (WBC)-reduction filters to prevent the alloimmunization of patients by the residual donor WBCs in filtered blood components transfused to them. Little attention has been paid to the capacity of current synthetic fiber filters to remove WBC membrane fragments bearing detectable leukocyte antigens. STUDY DESIGN AND METHODS: Fluorescein isothiocyanate-conjugated monoclonal antibody to a universal WBC membrane antigen (CD45) and high-speed centrifugation coupled with ficoll-hypaque differential sedimentation were used to quantitate low-density WBC fragments in single-donor platelet components before and after filtration to determine if a polyester fiber filter retained WBC fragments. RESULTS: Prefiltration measurements in 25 single-donor platelet components indicated that WBC fragments increased with length of storage up to 5 days at room temperature (p < 0.0001). When fragments in eight components were measured before and after filtration, absolute values for differences were insignificant (p = 0.15). CONCLUSION: WBC fragments were poorly retained by these polyester fiber WBC-reduction filters. The antigenicity of WBC fragments could contribute to the WBC alloimmunization of some recipients of WBC-reduced blood components.

Fatal outcome in a patient with autoimmune hemolytic anemia associated with an IgM bithermic anti-ITP.

BACKGROUND: Several cold autoantibodies (usually IgG) with IT specificity have been reported previously, as have autoantibodies with joint I and P blood group specificities (IP1, ITP1, iP1, IP). A fatal outcome associated with an IgM cold autoantibody of ITP specificity is reported. CASE REPORT: A 54-year-old man suffered from progressively severe cold autoimmune hemolytic anemia for 9 months. Hemoglobin concentration ranged from 6 to 7 g per dL (60-70 g/L) and reticulocytes from 3 to 5 percent (0.030-0.050). The direct antiglobulin test was weakly positive for IgM and strongly positive for C3d. The serum contained a cold agglutinin that reacted strongest with cord i red cells (RBCs) > adult I RBCs > adult i RBCs, which is consistent with IT specificity. The Donath-Landsteiner test was positive; the reaction was neutralized by globoside. The serum reacted weakly or was negative with RBCs from five group p blood donors, which suggests anti-ITP specificity. Dithiothreitol treatment of the serum abolished the cold agglutinin reactivity, which suggests that the anti-IT was IgM. The patient received > 40 RBC transfusions and failed to respond to oral steroids, oral cytoxan, high-dose pulse intravenous steroids, and plasma exchange at room temperature and at 35 degrees C. He died of sepsis following an unsuccessful trial of chlorambucil. Autopsy revealed unsuspected disseminated non-Hodgkin's lymphoma. CONCLUSION: Serologic studies are consistent with our patient's having a single IgM cold autoantibody with IT and P specificities (anti-ITP) and requiring both specificities on the same RBC to permit maximal antibody expression.