Flow cytometric evaluation of platelet activation in chronic autoimmune thrombocytopenia

Panzer, Simon; Höcker, Lisa; Vormittag, Rainer; Rieger, Miriam; Koren, Daniela; Dunkler, Daniela; Pabinger, Ingrid

doi:10.1002/pbc.21000

Cited by 18 publications

(18 citation statements)

References 15 publications

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“…However, in respect of the status of platelets with regard to activation, the subject had been contentious for three reasons: Firstly, all reports do not suggest that platelets in ITP patients were activated [13,18]. Secondly, reports that suggested platelet activation, were not always talking about the same thing; some mentioned activation of GPIIb/IIIa integrin through binding of PAC-1 antibody (which purports to assay the activation status of GPIIb/IIIa, through a single immunodiagnostic method, without fully establishing conformational change by other methods), while others focused on markers such as P-selectin and GPIb and GP53 (CD63) [13,[18][19][20]. Furthermore, the assays performed to check the activation status tend to assay ''activability'' as well, and different studies used different activating reagents such as thrombin and ADP.…”

Section: Discussionmentioning

confidence: 99%

Effect of steroids on the activation status of platelets in patients with Immune thrombocytopenia (ITP)

Bhoria¹,

Sharma²,

Varma

et al. 2014

Platelets

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The activation status of platelets in Immune Thrombocytopenia (ITP) patients--which is still somewhat controversial--is of potential interest, because activated platelets tend to aggregate (leading to excessive clotting or thromboembolic events) but cannot do so when platelet numbers are low, as in ITP. Although corticosteroids are the first line of therapy in ITP, the effect of steroids on activation of platelets has not been evaluated so far. We examined the status of platelet activation (with and without stimulation with ADP) in ITP patients, at the start of therapy (pre-steroid treatment, naive) and post-steroid treatment (classified on the basis of steroid responsiveness). We used flow cytometry to evaluate the levels of expression of P-selectin, and PAC-1 binding to platelets of 55 ITP patients and a similar number of healthy controls, treated with and without ADP. We found that platelets in ITP patients exist in an activated state. In patients who are responsive to steroids, the treatment reverses this situation. Also, the fold activation of platelets upon treatment with ADP is more in healthy controls than in ITP patients; treatment with steroids causes platelets in steroid-responsive patients to become more responsive to ADP-activation, similar to healthy controls. Thus steroids may cause changes in the ability of platelets to get activated with an agonist like ADP. Our results provide new insights into how, and why, steroid therapy helps in the treatment of ITP.

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Section: Discussionmentioning

confidence: 99%

Effect of steroids on the activation status of platelets in patients with Immune thrombocytopenia (ITP)

Bhoria¹,

Sharma²,

Varma

et al. 2014

Platelets

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“…26 Protein A immunoadsorption therapy reduced platelet associated IgG and IgM in ITP patients and also reduced the percentage of circulating P-selectin-positive platelets, suggesting an immune mechanism for the increased circulating P-selectin-positive platelets. 27 Panzer et al reported an increased percentage of circulating P-selectin-positive platelets in adult chronic ITP patients 28 and that ITP patients with high platelet surface P-selectin in vivo showed reduced agonist-induced platelet activation. 29 Panzer et al subsequently reported 6 that P-selectin expression on circulating platelets of ITP patients did not correlate with bleeding score, whereas platelet count and von Willebrand factordependent platelet adhesion were inversely associated with bleeding score.…”

Section: Discussionmentioning

confidence: 99%

Platelet function tests, independent of platelet count, are associated with bleeding severity in ITP

Frelinger

Grace

Gerrits

et al. 2015

Blood

132

123

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Key Points• ITP patients differ in their tendency to bleed despite similarly low platelet counts, thereby confounding treatment decisions.• Platelet function tests, independent of platelet count, are associated with bleeding severity in ITP patients.Immune thrombocytopenia (ITP) patients with similarly low platelet counts differ in their tendency to bleed. To determine if differences in platelet function in ITP patients account for this variation in bleeding tendency, we conducted a single-center, cross-sectional study of pediatric patients with ITP. Bleeding severity (assessed by standardized bleeding score) and platelet function (assessed by whole blood flow cytometry) with and without agonist stimulation was evaluated in 57 ITP patients (median age, 9.9 years). After adjustment for platelet count, higher levels of thrombin receptor activating peptide (TRAP)-stimulated percent P-selectin-and activated glycoprotein (GP)IIb-IIIa-positive platelets were significantly associated with a lower bleeding score, whereas higher levels of immature platelet fraction (IPF), TRAP-stimulated platelet surface CD42b, unstimulated platelet surface P-selectin, and platelet forward light scatter (FSC) were associated with a higher bleeding score. Thus, platelet function tests related to platelet age (IPF, FSC) and activation through the protease activated receptor 1 (PAR1) thrombin receptor (TRAPstimulated P-selectin, activated GPIIb-IIIa, and CD42b), independent of platelet count, are associated with concurrent bleeding severity in ITP. These tests may be useful markers of future bleeding risk in ITP. (Blood. 2015;126(7):873-879)

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“…CD16 ϩ cells are expanded under infectious or inflammatory conditions, 9,10 although the exact mechanism for increase in CD16 ϩ monocytes is not known. The activation state of platelets in ITP was reported to be inversely correlated with platelet counts, 36 and it may be that, in patients with low platelet counts, platelet-derived factors either directly or indirectly through activation of other mediators play a role in increased peripheral numbers of CD16 ϩ monocytes. For example, the chemokine CX3CL1/fractalkine known for its ability to promote the survival of CD16 ϩ monocytes 37 was elevated, albeit not statistically significant, in blood and bone marrow of ITP patients.…”

Section: Discussionmentioning

confidence: 99%

CD16+ monocytes control T-cell subset development in immune thrombocytopenia

Zhong

Bao

et al. 2012

Blood

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IntroductionClassic differentiation of naive CD4 ϩ T cells into different T helper (Th) subsets, including Th1, Th2, and Th17, occurs in lymphoid tissues after contact with antigen-presenting cells that produce polarizing cytokines. These Th subsets in turn orchestrate diverse immune responses also mediated by production of distinct cytokines. Because aberrant Th1 or Th17 activities have the potential to trigger chronic inflammatory and autoimmune diseases, 1,2 effector Th responses in healthy persons are under tight regulation mediated in part by CD4 ϩ regulatory T cells (Tregs) that are thymic-derived or naive T cell-inducible. 3 Understanding how Th1/Th17/Treg differentiation and expansion are controlled is likely to provide an explanation of how inflammation may be sustained in pathologic environments.More recently, human monocytes were shown to trigger and polarize Th responses 4,5 as well as to both stimulate and suppress T-cell responses during infection and in autoimmune diseases. 5,6 Monocytes, which are generally regarded as precursors of tissue macrophages and dendritic cells, 7 can be phenotypically divided based on surface expression of CD14 (lipopolysaccharide receptor) and CD16 (low affinity Fc␥ receptor III) expression into subsets, each with distinct functional activities. The major monocyte subpopulation characterized by high CD14 but no CD16 expression (CD14 hi CD16 Ϫ ), also referred to as classic monocytes, have higher phagocytic activity. 8 The minor CD16 ϩ cells produce higher TNF after stimulation and expand under infectious or inflammatory conditions. 9,10 With regards to the control of Th differentiation and reactivation, the specific role of the monocyte subsets has not been fully characterized.Immune thrombocytopenia (ITP) is an autoimmune bleeding disease resulting from decreased platelet production as well as accelerated platelet destruction mediated in part by autoantibody-based destruction mechanisms. 11 ITP patients harbor activated platelet-autoreactive T cells with increasing cytokine imbalance toward IL-2 and IFN-␥ 12-14 as well as altered Treg numbers and function. [15][16][17][18][19][20] A shift toward stimulatory monocytes with enhanced Fc␥R-mediated phagocytic capacity further supports a generalized immune dysregulation in ITP. 21 More recently, studies reported increased Th17 cells or IL-17 cytokine in ITP patients, 22-24 implicating a possible role for Th17 cells in ITP immunopathology, although 2 reports did not detect any difference. 25,26 Among the treatment options available to ITP patients, the recently licensed thrombopoietic agents, by increasing platelet production, have yielded overall durable responses in patients with persistent, chronic, and/or refractory ITP while on treatment. 27 Interestingly, improved Treg function in ITP patients was associated with increased platelet counts after the use of these agents, 28 despite apparent lack of immunomodulatory activity associated with such agents. Similarly, improved Treg compartment was reported in ITP patients w...

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Flow cytometric evaluation of platelet activation in chronic autoimmune thrombocytopenia

Cited by 18 publications

References 15 publications

Effect of steroids on the activation status of platelets in patients with Immune thrombocytopenia (ITP)

Effect of steroids on the activation status of platelets in patients with Immune thrombocytopenia (ITP)

Platelet function tests, independent of platelet count, are associated with bleeding severity in ITP

CD16+ monocytes control T-cell subset development in immune thrombocytopenia

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