Extracellular epitopes of platelet glycoprotein Ib alpha reactive with serum antibodies from patients with chronic idiopathic thrombocytopenic purpura

Glycoproteins (GPs) IIb/IIIa and Ib/IX are principal targets of autoantibodies (autoAbs) in idiopathic thrombocytopenic purpura (ITP). Platelet-associated Abs against GPIIb/IIIa primarily recognize discontinuous or nonlinear epitopes (Fujisawa et al, Blood 81:1284, 1993). This study focused on whether Abs against the extracellular domain of GPIb/IX might react with short linear amino acid (aa) sequences of GPIb alpha. Complementary DNAs (cDNAs) coding for two overlapping fragments of GPIb alpha were amplified, cloned into pFLAG.2 plasmids, and expressed in Escherichia coli DH5 alpha competent cells as FLAG fusion proteins, which were purified by anti-FLAG immunoaffinity chromatography. Of 16 selected ITP sera containing anti- GPIb/IX, 6 reacted in microtiter radioimmunoassays (RIAs) with recombinant protein fragment 2 (aas 240 to 485); 1 also with fragment 1 (aas 1 to 247). When synthetic peptides corresponding to 4 segments of fragment 2 with high antigenic indices (P1 to P4) were used as targets in RIAs, all 6 sera reacted with P2 (aas 326 to 346); 1 also reacted with P4 (aas 389 to 412). P2 was shown to be present on the surface of intact platelets by adsorption studies, and anti-P2 was detected in direct eluates of platelets from ITP patients. Glycocalicin in solution effectively competed with immobilized P2 for anti-P2; P2 in solution was a less effective competitor. Epitope scanning with a panel of synthetic 15-mer peptides localized the P2 epitope to the sequence, TKEQTTFPP. Epitope definition may offer insight into the pathophysiology of and more specific treatments for ITP.

Download Full-text

Spectrum of Ig classes, specificities, and titers of serum antiglycoproteins in chronic idiopathic thrombocytopenic purpura

Blood ◽

10.1182/blood.v83.4.1024.1024 ◽

1994 ◽

Vol 83 (4) ◽

pp. 1024-1032 ◽

Cited By ~ 133

Author(s):

R He ◽

DM Reid ◽

CE Jones ◽

NR Shulman

Keyword(s):

Idiopathic Thrombocytopenic Purpura ◽

Cytoplasmic Domain ◽

Platelet Glycoprotein ◽

Chronic Idiopathic Thrombocytopenic Purpura ◽

Platelet Destruction ◽

Thrombocytopenic Purpura ◽

Secondary Phenomenon ◽

Almost All ◽

Posttransfusion Purpura ◽

Detectable Serum

Abstract The characteristic decreased recovery and survival of transfused platelets in nonalloimmunized patients with idiopathic thrombocytopenic purpura (ITP) suggest that plasma antiplatelet autoantibodies (autoAbs) are present in almost all cases. Studies emphasizing reactions of IgG autoAbs with platelet glycoprotein (GP) IIb/IIIa indicate that less than 50% of ITP patients have detectable serum Abs, and that many of these Abs may not be pathogenic because they are directed against epitopes in the cytoplasmic domain of GPIIIa (Fujisawa et al, Blood 77:2207, 1991 and 79:1441, 1992). We evaluated the contribution of Ig classes other than IgG to the overall incidence of serum Abs in 47 patients with chronic ITP and the frequency of reactions with GPs IIb/IIIa, Ib/IX, IV, and Ia/IIa. Abs were further characterized by their reactions with cytosolic or exosolic GP epitopes and their titers and apparent affinities. Using immunobead techniques we found (1) anti- GPs in 85% of sera; (2) IgA and IgG Abs each in 68%, together in 51%; (3) IgM agglutinins in 15%, always with another Ab class; (4) GP Ib/IX, IIb/IIIa, IV, and Ia/IIa targets in 83%, 81%, 38%, and 28% of cases, respectively; (5) 93% of positive sera reactive with more than one GP; but GP IV or Ia/IIa never the sole target; (6) Abs against cytosolic epitopes on one or more of GPs IIIa, Ib alpha, and IIb beta in 66% of sera, always accompanied by Abs against exosolic epitopes of the same or a different GP; (7) autoAbs against cytosolic GP epitopes in 38% of 16 patients recovered from posttransfusion purpura and drug purpura; and (8) evidence that serum ITP Abs, often high-titered, saturate platelets less than alloAbs against the same GPs. Whereas Abs against external GP epitopes are a distinctive marker for ITP in 80% of patients, Abs against internal GP epitopes are likely a secondary phenomenon of platelet destruction and not pathogenic. Anti-GPs against exosolic epitopes were also found in eluates of patients platelets', suggesting that they have pathogenic significance.

Download Full-text

Autoantibodies to Platelet Glycoprotein IIb/IIIa and to the Acetylcholine Receptor in a Patient with Chronic Idiopathic Thrombocytopenic Purpura and Myasthenia Gravis

Annals of Internal Medicine ◽

10.7326/0003-4819-100-6-829 ◽

1984 ◽

Vol 100 (6) ◽

pp. 829 ◽

Cited By ~ 9

Author(s):

MICHAEL J. ANDERSON

Keyword(s):

Myasthenia Gravis ◽

Acetylcholine Receptor ◽

Idiopathic Thrombocytopenic Purpura ◽

Platelet Glycoprotein ◽

Chronic Idiopathic Thrombocytopenic Purpura ◽

Thrombocytopenic Purpura

Download Full-text

Platelet glycoprotein IIb as a target antigen in two patients with chronic idiopathic thrombocytopenic purpura

British Journal of Haematology ◽

10.1111/j.1365-2141.1987.tb01340.x ◽

1987 ◽

Vol 66 (4) ◽

pp. 535-538 ◽

Cited By ~ 36

Author(s):

Y. Tomiyama ◽

Y. Kurata ◽

H. Mizutani ◽

Y. Kanakura ◽

T. Tsubakio ◽

...

Keyword(s):

Idiopathic Thrombocytopenic Purpura ◽

Platelet Glycoprotein ◽

Target Antigen ◽

Chronic Idiopathic Thrombocytopenic Purpura ◽

Thrombocytopenic Purpura

Download Full-text

Spectrum of Ig classes, specificities, and titers of serum antiglycoproteins in chronic idiopathic thrombocytopenic purpura

Blood ◽

10.1182/blood.v83.4.1024.bloodjournal8341024 ◽

1994 ◽

Vol 83 (4) ◽

pp. 1024-1032 ◽

Cited By ~ 4

Author(s):

R He ◽

DM Reid ◽

CE Jones ◽

NR Shulman

Keyword(s):

Idiopathic Thrombocytopenic Purpura ◽

Cytoplasmic Domain ◽

Platelet Glycoprotein ◽

Chronic Idiopathic Thrombocytopenic Purpura ◽

Platelet Destruction ◽

Thrombocytopenic Purpura ◽

Secondary Phenomenon ◽

Almost All ◽

Posttransfusion Purpura ◽

Detectable Serum

The characteristic decreased recovery and survival of transfused platelets in nonalloimmunized patients with idiopathic thrombocytopenic purpura (ITP) suggest that plasma antiplatelet autoantibodies (autoAbs) are present in almost all cases. Studies emphasizing reactions of IgG autoAbs with platelet glycoprotein (GP) IIb/IIIa indicate that less than 50% of ITP patients have detectable serum Abs, and that many of these Abs may not be pathogenic because they are directed against epitopes in the cytoplasmic domain of GPIIIa (Fujisawa et al, Blood 77:2207, 1991 and 79:1441, 1992). We evaluated the contribution of Ig classes other than IgG to the overall incidence of serum Abs in 47 patients with chronic ITP and the frequency of reactions with GPs IIb/IIIa, Ib/IX, IV, and Ia/IIa. Abs were further characterized by their reactions with cytosolic or exosolic GP epitopes and their titers and apparent affinities. Using immunobead techniques we found (1) anti- GPs in 85% of sera; (2) IgA and IgG Abs each in 68%, together in 51%; (3) IgM agglutinins in 15%, always with another Ab class; (4) GP Ib/IX, IIb/IIIa, IV, and Ia/IIa targets in 83%, 81%, 38%, and 28% of cases, respectively; (5) 93% of positive sera reactive with more than one GP; but GP IV or Ia/IIa never the sole target; (6) Abs against cytosolic epitopes on one or more of GPs IIIa, Ib alpha, and IIb beta in 66% of sera, always accompanied by Abs against exosolic epitopes of the same or a different GP; (7) autoAbs against cytosolic GP epitopes in 38% of 16 patients recovered from posttransfusion purpura and drug purpura; and (8) evidence that serum ITP Abs, often high-titered, saturate platelets less than alloAbs against the same GPs. Whereas Abs against external GP epitopes are a distinctive marker for ITP in 80% of patients, Abs against internal GP epitopes are likely a secondary phenomenon of platelet destruction and not pathogenic. Anti-GPs against exosolic epitopes were also found in eluates of patients platelets', suggesting that they have pathogenic significance.

Download Full-text

Faculty Opinions recommendation of Effect of eltrombopag on platelet counts and bleeding during treatment of chronic idiopathic thrombocytopenic purpura: a randomised, double-blind, placebo-controlled trial.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1922956.1476054 ◽

2010 ◽

Author(s):

John Feiner

Keyword(s):

Idiopathic Thrombocytopenic Purpura ◽

Controlled Trial ◽

Chronic Idiopathic Thrombocytopenic Purpura ◽

Double Blind ◽

Thrombocytopenic Purpura ◽

Double Blind Placebo ◽

Platelet Counts

Download Full-text

Acute kidney injury and nephrotic syndrome associated with eltrombopag therapy in chronic idiopathic thrombocytopenic purpura

BMJ Case Reports ◽

10.1136/bcr-2020-241462 ◽

2021 ◽

Vol 14 (4) ◽

pp. e241462

Author(s):

Suchi Anindita Ghosh ◽

Jean Patrick ◽

Kyaw Zin Maw

Keyword(s):

Acute Kidney Injury ◽

Renal Failure ◽

Nephrotic Syndrome ◽

Idiopathic Thrombocytopenic Purpura ◽

Kidney Injury ◽

High Dose ◽

Chronic Idiopathic Thrombocytopenic Purpura ◽

Thrombocytopenic Purpura ◽

Antibody Screen ◽

Auto Antibody

A 77-year-old man was admitted with severe acute kidney injury and nephrotic syndrome. He was started on eltrombopag for chronic idiopathic thrombocytopenic purpura 6 weeks earlier. An ultrasound of the kidneys was normal and an auto-antibody screen was negative. The use of the Naranjo adverse drug reaction probability scale indicated a probable relationship (score of 5) between the patient’s development of acute renal failure and eltrombopag therapy. Literature review identified only one other case of nephrotic syndrome and acute kidney injury associated with eltrombopag therapy in which a kidney biopsy revealed focal segmental glomerulosclerosis. Due to the challenges faced during the prevailing SARS-CoV-2 pandemic and persistent low platelet counts a renal biopsy was not undertaken. On stopping eltrombopag, the patients renal function stabilised and he successfully went into remission following treatment with high dose corticosteroids and diuretics. This report of a serious case of reversible renal failure and nephrotic syndrome after treatment with eltrombopag may serve to inform clinicians about the possible severe renal adverse effects of eltrombopag before its commencement for future use.

Download Full-text