Polyphosphates form antigenic complexes with platelet factor 4 (PF4) and enhance PF4-binding to bacteria

Brandt, Sven Van; Krauel, Krystin; Jaax, Miriam E.; Renné, Thomas; Helm, Christiane A.; Hammerschmidt, Sven; Delcea, Mihaela; Greinacher, Andreas

doi:10.1160/th15-01-0062

Cited by 42 publications

(54 citation statements)

References 58 publications

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“…Mice injected with PF4/nucleic acid complexes develop antibodies that cross-reacted with PF4/ heparin complexes (30). Our microfluidic channel experiments support that PF4 forms complexes with chromatin DNA in the same way as PF4 binds heparin to form macroaggregates (40). Our studies showing that HIT IgG isolated from human plasma binds to these PF4-NET complexes confirm that they contain HIT antigenic epitopes.…”

Section: Discussionsupporting

confidence: 68%

Neutrophil accumulation and NET release contribute to thrombosis in HIT

Gollomp¹,

Kim²,

Johnston³

et al. 2018

JCI Insight

131

176

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Heparin-induced thrombocytopenia (HIT) is an immune-mediated thrombocytopenic disorder associated with a severe prothrombotic state. We investigated whether neutrophils and neutrophil extracellular traps (NETs) contribute to the development of thrombosis in HIT. Using an endothelialized microfluidic system and a murine passive immunization model, we show that HIT induction leads to increased neutrophil adherence to venous endothelium. In HIT mice, endothelial adherence is enhanced immediately downstream of nascent venous thrombi, after which neutrophils undergo retrograde migration via a CXCR2-dependent mechanism to accumulate into the thrombi. Using a microfluidic system, we found that PF4 binds to NETs, leading them to become compact and DNase resistant. PF4-NET complexes selectively bind HIT antibodies, which further protect them from nuclease digestion. In HIT mice, inhibition of NET formation through Padi4 gene disruption or DNase treatment limited venous thrombus size. PAD4 inactivation did affect arterial thrombi or severity of thrombocytopenia in HIT. Thus, neutrophil activation contributes to the development of venous thrombosis in HIT by enhancing neutrophil-endothelial adhesion and neutrophil clot infiltration, where incorporated PF4-NET-HIT antibody complexes lead to thrombosis propagation. Inhibition of neutrophil endothelial adhesion, prevention of neutrophil chemokine-dependent recruitment of neutrophils to thrombi, or suppression of NET release should be explored as strategies to prevent venous thrombosis in HIT.

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Section: Discussionsupporting

confidence: 68%

Neutrophil accumulation and NET release contribute to thrombosis in HIT

Gollomp¹,

Kim²,

Johnston³

et al. 2018

JCI Insight

131

176

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“…These studies affirm that PF4 can form antigenic complexes with polyphosphates of diverse sizes ranging from those released by platelets to those released by bacteria 20 (Figure 1). The latter suggests a potential new link between the postulated binding of PF4 to bacteria and the genesis of anti-PF4 antibodies responsible for HIT.…”

Section: Discussionsupporting

confidence: 67%

“…One clue toward identifying the pathways that might predispose to delayed thrombotic complications in patients with HIT is the finding that PF4 forms antigenic complexes with a variety of polyanions, including glycosaminoglycans, sulfated anticoagulants, lipid A from gram-negative bacteria, RNA, and inorganic polyphosphates (polyPs). 2,4,[18][19][20][21][22] PolyPs are highly anionic linear polymers of orthophosphate linked by phosphoanhydride bonds. [23][24][25] Although found in all mammalian cells, polyPs are present in the dense granules of human platelets at millimolar concentrations and are released following activation.…”

Section: Introductionmentioning

confidence: 99%

Polyphosphate/platelet factor 4 complexes can mediate heparin-independent platelet activation in heparin-induced thrombocytopenia

et al. 2016

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Heparin-induced thrombocytopenia (HIT) is a thrombotic disorder initiated by antibodies to complexes between platelet factor 4 (PF4) and heparin. The risk of recurrent thromboembolism persists after heparin is cleared and platelet activation leading to release of PF4 has dissipated. We asked whether antigenic complexes between polyphosphates and PF4 released from activated platelets might intensify or sustain the prothrombotic phenotype of HIT. PF4 forms stable, ultralarge complexes with polyphosphates of various sizes, including those released from platelets, which are recognized by the HIT-like monoclonal KKO, an immunoglobulin G2bκ monoclonal heparin/PF4 binding antibody, and by human HIT antibodies. KKO helps to protect PF4/polyphosphate complexes from degradation by phosphatases. Complement is activated when HIT antibodies bind to PF4/polyphosphate complexes and PF4 reverses the inhibition of complement by polyphosphates. Polyphosphates and PF4 are stored primarily in separate granules in resting platelets, but they colocalize when the cells are activated. Platelets activated by subaggregating doses of thrombin receptor activating peptide release polyphosphates and PF4, which form antigenic complexes that allow KKO to further activate platelets in the absence of heparin and exogenous PF4. These studies suggest that thrombin- or immune complex-mediated release of endogenous antigenic PF4/polyphosphate complexes from platelets may augment the prothrombotic risk of HIT and perpetuate the risk of thrombosis after heparin has been discontinued.

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“…LPS reaches a length of up to 25 nm, therefore sterically hiding the Fc part of the IgG for the platelet Fc receptor, as the complex of PF4/lipid A with a bound anti‐PF4/P IgG cannot reach out of the LPS cover. However, we have also shown that polyphosphates can overcome the inhibitory effect of longer LPS chains by forming larger PF4/polyphosphate complexes .…”

Section: Discussionmentioning

confidence: 76%

Platelets kill bacteria by bridging innate and adaptive immunity via platelet factor 4 and FcγRIIA

Palankar

Kohler

Krauel

et al. 2018

Journal of Thrombosis and Haemostasis

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Background Activated platelets release the chemokine platelet factor 4 (PF4) stored in their granules. PF4 binds to polyanions (P) on bacteria, undergoes a conformational change and exposes neoepitopes. These neoepitopes induce production of anti-PF4/P antibodies. As PF4 binds to a variety of bacteria, anti-PF4/P IgG can bind and opsonize several bacterial species. Objective Here we investigated whether platelets are able to kill bacteria directly after recognizing anti-PF4/P IgG opsonized bacteria in the presence of PF4 via their FcγRIIA. Methods Using platelet-bacteria suspension co-culture experiments and micropatterns with immobilized viable bacteria, in combination with pharmacological inhibitors and human anti- PF4/P IgG we analyzed the role of platelet-mediated killing of bacteria. Results In the presence of PF4, human anti-PF4/P IgG and platelets, E. coli killing (> 50%) with colony forming units (CFU mL ) 0.71 × 10 ± 0.19 was observed compared with controls incubated only with anti-PF4/P IgG (CFU mL 3.4 × 10 ± 0.38). Blocking of platelet FcγRIIA using mAb IV.3 (CFU mL 2.5 × 10 ± 0.45), or integrin αIIbβ3 (CFU mL 2.26 × 10 ± 0.31), or disruption of cytoskeletal functions (CFU mL 2.7 × 10 ± 0.4) markedly reduced E. coli killing by this mechanism. Our observation of E. coli killing by platelets on micropatterned arrays is compatible with the model that platelets kill bacteria by covering them, actively concentrating them into the area under their granulomere and then releasing antimicrobial substances of platelet α-granules site directed towards bacteria. Conclusion These findings collectively indicate that by bridging of innate and adaptive immune mechanisms, platelets and anti-PF4/polyanion antibodies cooperate in an antibacterial host response.

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Polyphosphates form antigenic complexes with platelet factor 4 (PF4) and enhance PF4-binding to bacteria

Cited by 42 publications

References 58 publications

Neutrophil accumulation and NET release contribute to thrombosis in HIT

Neutrophil accumulation and NET release contribute to thrombosis in HIT

Polyphosphate/platelet factor 4 complexes can mediate heparin-independent platelet activation in heparin-induced thrombocytopenia

Platelets kill bacteria by bridging innate and adaptive immunity via platelet factor 4 and FcγRIIA

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