Enhanced activation of platelets with abnormal release of RANTES in human immunodeficiency virus type 1 infection

Abstract

Besides their role in hemostasis, platelets are involved in inflammatory and immunological processes, and we hypothesize that platelet activation may play an immunopathogenetic role in HIV-1 infection. Blood was drawn from 15 controls and 20 HIV-1-infected patients with normal platelet counts, classified into groups of non-AIDS and AIDS. Platelet activation was detected using flow cytometry with mAbs against the release markers P-selectin and CD63, mAb against GPIb, and the probe annexin V detecting surface exposure of aminophospholipids. The amount of microvesicles was measured using mAb against GPIIIa. Compared to controls, blood samples from HIV-1-infected patients showed significantly enhanced levels of microvesicles and activated platelets as detected by their exposure of P-selectin, CD63, and aminophospholipids, as well as reduction in GPIb expression. Increased expression of P-selectin and amounts of microvesicles were most pronounced in advanced clinical and immunological disease. When studying the effect of HIV-1 protease inhibitor therapy (indinavir) on platelet activation, we found that concomitant with a profound decrease in plasma viral load, there was a near normalization of several of the parameters reflecting enhanced platelet activation. Finally, we demonstrated that platelets may be an important source of the chemokine RANTES in HIV-1-infected patients. Although both unstimulated and SFLLRN-stimulated platelets from asymptomatic patients had enhanced release of RANTES, platelets from AIDS patients were characterized by markedly enhanced spontaneous, but decreased SFLLRN-stimulated release of this chemokine. Taken together, these results, which demonstrate for the first time increased platelet activation in HIV-1-infected patients with normal platelet counts, may represent a previously unrecognized immunopathogenic factor in HIV-1 infection.

Identification of the platelet-derived chemokine CXCL4/PF-4 as a broad-spectrum HIV-1 inhibitor

“…These massive amounts of CXCL4 are deemed to be necessary to trigger the initial phase of hemostasis (24); yet, CXCL4 also exerts immunomodulatory and proinflammatory effects, especially by promoting monocyte activation and differentiation (32). These properties of CXCL4 may be of particular clinical relevance when platelets are abnormally activated in the course of inflammatory processes (13)(14)(15)(16) including HIV-1 infection where a variety of platelet anomalies have been described associated with sustained platelet activation and increased tendency toward thrombosis (17)(18)(19)(20)(21)(22). Thus, CXCL4 may play a dual role in the pathogenesis of HIV-1 disease, on one side by suppressing HIV-1 replication but on the other by fostering immunologic activation, inflammation, and coagulation abnormalities.…”

“…In addition, platelet alterations, including abnormal platelet activation and apoptosis, are frequently detected in HIV-1-infected individuals even with normal platelet counts (21,22). Sustained platelet activation in these subjects may be due, at least in part, to direct binding and internalization of HIV-1 virions by platelets, mediated by the C-type lectin receptors CLEC-2 and DC-SIGN (23).…”

Enhanced Levels of Soluble and Membrane-Bound CD40 Ligand in Patients With Unstable Angina

“…From time to time, circulating platelets in patients with unstable angina may well encounter a secretioninducing "event," eg, contact with "foreign surfaces" at an atherosclerotic lesion, and such stimuli may possibly be potentiated by enhanced levels of proinflammatory cytokines, eg, TNF␣. 18 Such an in vivo activation may induce a marked degranulation in a small but significant proportion of platelets, resulting in a persistently higher proportion of degranulated platelets in these patients. A similar pattern of decreased SFLLRN-stimulated platelet activation ex vivo, reflecting enhanced platelet activation in vivo, has recently been reported in patients with septic shock 30 and AIDS.…”

“…18 Briefly, a volume of 475 L of PRP was incubated by gentle tilting for 30 minutes at room temperature after the addition of 25 L of the thrombin receptoragonist peptide SFLLRN (Biotechnology Center of Oslo, Norway; final concentration, 100 mol/L) or Tris-buffered saline only (unstimulated sample). At baseline and after 30 minutes, equal volumes of PRP were centrifuged at 11,000g and 4°C for 10 minutes, and platelet-free supernatant and a platelet pellet with 500 L of Tris-buffered saline were stored separately at Ϫ80°C.…”

Functional Synergy between CD40 Ligand and HIV-1 Tat Contributes to Inflammation: Implications in HIV Type 1 Dementia

“…These cells were chosen for three reasons: 1) HIV-1 infection is associated with elevated levels of markers of platelet activation, regardless of HAART (14 -16, 19), 2) increased numbers of circulating activated platelets have been detected in the plasma of HIV-1-infected patients, both before and after antiretroviral therapy (38,39), and 3) sCD40L in plasma is believed to arise almost solely (95%) from activated platelets (40). In these assays, we exposed human platelets either to thrombin, a powerful platelet activator, to the HIV-1 gene products Tat and gp120, or to PAF, a proinflammatory mediator that has been implicated in the pathogenesis of HAD (16).…”