Platelets in Autoimmune Disorders: Physiology & Pathology

In the name of God the role of platelets in the physiology and pathology of autoimmune disorders Dr.Alireza farsinejad Supervisor: Zahra Barzang Presented by: 1

the role of platelets 1-Hemostasis 2-Thrombosis 3-Malignancy 4-Inflammation 5-Wound healing 6-Innate immunity 7-Adaptive immunity 8-Autoimmune disorders 2

Platelet adhesion 3

Platelet activation and granule secretion 4

Platelet aggregation 5

Platelets surface receptors Glycoprotein integrin IIb 3 (GPIIb/IIIa) toll-like receptors (TLRs) Glycoprotein Ib-IX-V receptor complex P-selectin 6

Platelets granules alpha granules dense granules lysosomes 7

synthesize protein in platelet sources other than megakaryo cytes absorbed from plasma the generated de novo 8

Platelet microRNA miR-146a miR-155 9

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Platelet neutrophils 11

NETosis 12

Platelet lymphocytes The co-culturing of autologous platelets and CD4 + T cells enhanced the production of IL-10 and cytokines characteristic for Th1 and Th17 cells: IFN , IL-17 Th1 and Th17, which are associated with autoimmunity. The co-incubation of differentiated B cells with activated platelets was associated with increased in vitro production of IgG1, IgG2, and IgG3 13

Transcellular synthesis of bioactive lipid mediators 14

Evidence for platelet contribution in autoimmune disorders 15

Rheumatoid arthritis (RA) Cardiovascular disease is the leading cause of death in RA patients Multiple evidence point towards increased platelet activation in RA patients. Many of them have an increased platelet count. Intensified platelet production results in higher percentage of young platelets in circulation. Younger platelets are characterized by enlarged size and higher reactivity. Increased amount of soluble platelet releasates, such as: P-selectin, beta-thromboglobulin, or PF4, are found in the serum of RA patients Increased platelet activation, assessed with these indicators, correlates positively with disease severity 16

NETosis In mouse, model of RA platelet depletion leads to inflammation alleviation. In the serum of RA patients, immune complex and autoantibody characteristics for RA can activate platelets. This includes anti-citrullinated protein antibodies (ACPA) and rheumatoid factor (RF). ACPA IgE immune complexes may activate platelets via FccRIIA and FceRIa high- and low-affinity receptor (FceRII/CD23) for IgE, and low-affinity immunoglobulin G (IgG) receptor (Fc RIIa) Elevated PMP counts were found not only in plasma, but also in the synovial fluid of RA patients. 17

Signaling pathways involve in NET formation PMP concentration in synovial fluids was significantly higher than in blood. IL-1, so abundant in synovial fluid PMP, is the key molecule for intercommunication between platelets and fibroblast-like synoviocytes (FLS) . Activated FLS are regarded as key effectors of cartilage destruction. RA patients FLS express altered levels of cytokines, chemokines, adhesion molecules, and matrix metalloproteinases, and they also become resistant to apoptosis. 18

platelets and FLS produce prostaglandin I2 (PGI2). PMP stimulate up-regulation of eicosanoid synthesis enzymes: COX-2, microsomal prostaglandin E synthase 1 (mPGES1), and PGE2. PGE2 itself enhances the expression of membrane-bound mPGE. In a mouse, model of RA resolution of inflammation is disrupted by inhibition of COX-2, but can be restored by lipoxins . PMP in the synovial fluid of RA patients are highly heterogeneous in size. 19

Differences between NETosis and other cell death PMP express platelet-derived antigens and associate with autoantigens from other sources that are present in plasma . Platelet-derived antigens include intracellular proteins, such as vimentin. PMP surface may be a site of further post-transcriptional autoantigen modifications, for example, citrullinisation. Complement proteins can bind to PMP surface. Highly bound C1q, C3, and C4 complement components are characteristic for PMP in the synovial fluid of RA patients. These immune complexes were showed to strongly activate neutrophils. Upheld activation of platelets and neutrophils results in NETosis which, in turn, strongly activates FLS. 20

Systemic Sclerosis (SSc) Systemic sclerosis (SSc) is an inflammatory disease and an autoimmune disorder characterized by widespread organ dysfunction due to excessive accumulation of collagen in organs, fibrosis and ischemia. enlarged von Willebrand multimers were found in their plasma. 21

Systemic Sclerosis (SSc) 22

Systemic lupus Erythematosus (SLE) Systemic lupus Erythematosus (SLE) is a systemic auto-immune disorder characterized by formation of autoantibodies and immune complexes, tissues and organ damage. Thrombocytopenia is often found in SLE patient. 23

Systemic lupus Erythematosus (SLE) SLE patient have symptoms such as kidney injury, haemolytic anaemia, neuropsychiatric manifestations. The markers of platelet activation are increased in SLE patients such as thromboxane, P-selectin, PMP, and platelet-Leukocyte aggregates. The main activators of platelets in SLE such as immune complexes, antiphospholipid antibodies. In activation platelets increase type I interferon production, NETosis, dendritic cell activation, and T and B lymphocyte activation, all cause the development of SLE. 24

Systemic lupus Erythematosus (SLE) Activated platelets contribute to the maturation of dendritic cells (DC). dendritic cells are crucial in the pathogenesis of SLE, as their interactions with B- and T cells lead to the production of autoantibodies, including those against nuclear antigens (ANA) and DNA (anti-ds-DNA). PMP-associated CD154 can cause DC activation and soluble CD154 levels were found to be increased in SLE patients and to correlate with disease activity measured by SLE Disease Activity Index. . Level of CD154 correlates positively with the presence of anti-phospholipid antibodies in SLE patients 25

Systemic lupus Erythematosus NET function in immune system (SLE) platelets from SLE patients were found to over-express IFN-regulated genes, resulting in up-regulated numbers of the proteins PRKRA, IFITM1, and CD69 leading to increased activation of platelets from SLE patients associated with the type I IFN response. Platelet autoantibodies were found in SLE patients. Circulating PMP in SLE patients carry increased loads of IgG, IgM, and C1q . PMP-IC elicit leukotriene production and NET generation by neutrophils . 26

Systemic lupus Erythematosus (SLE) NET degradation is impaired in SLE, and patients with defective NET degradation have significantly higher titres of anti-NET andanti-ds-DNA autoantibodies, as well as a higher frequency of developing lupus nephritis. Platelet activation seems to be a potential link between atherosclerotic lesions and systemic inflammation . 27

Anti-phospholipid Syndrome (APS) Anti-phospholipid syndrome (APS) is an autoimmune disorder associated with thrombotic, activation apoptosis, cardiovascular risk and high levels of pathogenic antiphospholipid antibodies (aPL). Anti-phospholipid antibodies (aPL) are present in autoimmune disorders such as SLE, RA, SSc. Anti-phospholipid antibodies (APL), particularly lupus anticoagulant, anticardiolipin antibodies (aCL), and anti- (2)-glycoprotein I (anti- 2 GPI), are antibodies against phospholipids and these antibodies interfere with the membrane phospholipids of endothelial cells and platelets and participate in coagulation cascade In APS patients there are autoantibodies against platelet 2-glycoprotein I ( 2-GPI). 28

Anti-phospholipid NET function in inflammatory diseases Syndrome (APS) Thrombocytopenia is commonly observed among APS patients, and the most common determinant autoantigen described is platelet 2-glycoprotein I ( 2-GPI). 2-GPI is an apolipoprotein which plays a complex role in blood coagulation. Binding the autoantibodies to 2-GPI results in the formation of a macromolecular complex, PF4- 2-GPI anti- 2-GPI, that contributes significantly to platelet activation. Enhanced platelet activation sustained over time is related to vascular dysfunction and progressive damage, thrombotic events, and complement activation. 29

Anti-phospholipid Syndrome (APS) Immune complexes containing C4d and C3b complement proteins have been found to be deposited in the placentas of APS patients. PMP are significantly increased in APS patients, especially in those with APS secondary to SLE or patients with a history of thrombotic complications. In APS patients there are higher level of platelet-derived bioactive releasates such as CXCL4 (PF4). PF4 interacts with the anti- 2-GPI- 2-GPI macromolecule in APS patients, cause enhances platelet activation. 30

Conclusions Platelets have role in autoimmune disorders. Platelets have role in autoimmune inflammation including: extensive complement activation, circulation of immune complexes, and NETs. Platelets contribute in autoimmunity such as: promote T helper leukocyte maturation towards type 1 and type 17, thrombosis, atherosclerosis. Platelets play an opposite role including: the production pro- or anti-inflammyator. . Platelet-rich plasma (PRP) infusions are widely applied in treating joint trauma, as platelet-derived growth factors have a positive influence on chondrocytes . 31

Thanks for your attention 32