Investigating platelet function and immune activation in HIV-infection

Nkambule, Bongani Brian (2015-04)

Thesis (PhD)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Introduction In the era of antiretroviral therapy (ART), people living with Human Immunodeficiency Virus (HIV) now have prolonged life spans. An emerging trend of non- acquired immune deficiency syndrome (AIDS) related complications now prevails in the aging HIV infected population. Increased levels of inflammation and chronic immune activation are associated with HIV infection. In the era of ART people living with HIV are at an increased risk of cardiovascular disease (CVD). Platelets play a pivotal role in both inflammation and immune activation and upon activation platelets degranulate and secrete various inflammatory, coagulatory and adhesion molecules. Activated platelets express surface P-selectin (CD62P) and are a key component of the coagulation pathway and serve as a link between inflammation and thrombosis. Activated platelets have been implicated in inflammatory and cardiovascular disease and have been identified as immune cells that play a crucial role in pathogen recognition and modulation of immune cells during infections. Several antiviral and antibacterial properties of platelet alpha granule contents have been established. Platelet aggregometry remains the most widely used technique to evaluate platelet function even though this technique is limited by many pre-analytical variables. Platelet flow cytometry on the other hand offers a rapid measurement of platelet function in their physiological environment with minimal artefactual activation. Few studies have however reported on standardized methods to evaluate platelet function in the context of HIV. Platelet function remains unclear and data on HIV infected treatment naïve individuals remains scarce. The aim of this project was to examine the relationship between platelet function and immune activation in patients with HIV Materials and methods This study consisted of five sub-studies, firstly platelet indices and levels of platelet activation were determined in a cohort of 330 participants (185 HIV infected ARV naïve and 145 uninfected healthy controls) using; flow cytometry and haemotology analyzers. The relationship between these indices and markers of platelet activation, disease progression and immune activation were assessed. Furthermore, levels of platelet activation and aggregation were evaluated in a cohort of 82 participants (41 HIV infected (ARV naïve) individuals and 41 uninfected healthy controls), using a novel whole blood flow cytometry based functional assay. These baseline levels were then correlated with markers of immune activation and disease progression in HIV. In a subsequent study, platelet function in a cohort consisting of 58 HIV infected (ARV naïve) and 38 uninfected controls was evaluated using flow cytometry. Platelet response was measured post stimulation with adenosine diphosphate (ADP) at concentrations known to induce reversible (0.04mM) and irreversible (0.2mM) platelet aggregation. In order to assess platelet function in HIV, platelet response was evaluated in a cohort consisting of 58 HIV infected (ARV naïve) and 38 uninfected controls. Platelets were activated using varying concentrations of ADP, arachidonic acid (AA) and collagen and platelet function was measured using flow cytometry. Levels of circulating platelet leukocyte aggregates (PLAs) were also measured using flow cytometry in a cohort consisting of 35 HIV-infected (ARV naïve) individuals and 32 uninfected healthy controls. Associations between PLAs, immune activation and disease progression in HIV infected individuals were determined. The final study evaluated platelet aggregates, platelet derived microparticles (PMPs) and microparticles (MPs) in a cohort consisting of 46 HIV infected (ARV-naïve) and 40 uninfected healthy controls. Associations between MPs, PMPs, platelet aggregates and markers of immune activation and disease progression were evaluated. Results HIV infected individuals showed decreased mean platelet volume levels (HIV mean 7.91 ± 0.85 vs. 8.52 ± 1.12, p<0.0001) that directly correlated with CD4 counts (r=-0.2898, p=0.0075) and viral load (r=0.2680, p=0.0177). Platelet distribution width (PDW) levels directly correlated (r=0.3455, p=0.0362) with active coagulation and inversely correlated (r=-0.3666, p=0.0463) with platelet aggregation. HIV infected individuals showed increased levels of platelet activation (%CD62P median 11.33[5.96-29.36] vs. control group 2.48[1.56-6.04], p=0.0001). In HIV, platelet function is retained and platelets showed increased response to submaximal concentrations of endogenous agonists. HIV infected individuals showed increased levels of circulating platelet monocyte aggregates (25.26[16.16-32.28] vs. control group 14.12[8.36- 18.83], p=0.0001) that directly correlated with markers of immune activation; %CD38/8 (r=0.54624, p=0.0155), viral load (r=0.633, p<0.009). Furthermore we report on increased levels of circulating MPs (median %MPs 1.7[0.95-2.83] vs. Control group 1.12[0.63-1.57], p=0.0160); PMPs (median %PMPs 26.64[11.33-36.62] vs. Control group 20.02[18.08-26.08], p=0.0133); activated PMPs (median CD62P MFI 3.81[3.46-4.54] vs. Control group 3.41[3.16-3.6], p=0.0037) and platelet aggregates (Median %CD62P 14.10[5.49-39.94] vs. Control group 0.17[0.10-10.99], p= 0.0097) in HIV infected asymptomatic individuals. Conclusion This study supports the potential use of the MPV and PDW as readily available markers of platelet activation and immune activation in HIV. We also showed elevated levels of activated platelets in HIV infected individuals that were hyper responsive to endogenous agonists in a concentration dependent manner. Platelet flow cytometry is a rapid and valuable technique in the evaluation of platelet function in HIV. The measurement of platelet function using flow cytometry allows the evaluation of platelet signalling pathways that may be modified in HIV infected individuals. Lastly we describe an optimized whole blood flow cytometry based assay for the evaluation of circulating microparticles (MPs), platelet derived microparticles (PMPs) and levels of activated platelets and aggregates which mimics the in vivo physiological environment of MPs. To the best of our knowledge, this study is the first to report on a novel approach in evaluating platelet function in HIV using a series of optimised whole blood flow cytometry based platelet assays. In addition, minimal work has been performed previously on platelet function in the context of HIV-infection; and particularly in a cohort of asymptomatic, untreated patients as defined for this study.

AFRIKAANSE OPSOMMING: Inleiding In die era van antiretrovirale terapie (ART), het mense wat met die menslike immuniteitsgebreksvirus (MIV) leef, het nou 'n verlengde lewensduur. 'N opkomende neiging van nie-verworwe immuniteitsgebreksindroom (vigs) heers nou in die verouderende MIV-besmette bevolking. Verhoogde vlakke van inflammasie en chroniese immuun aktivering word geassosieer met MIV-infeksie en in die era van ART loop mense wat met MIV leef, 'n verhoogde risiko van kardiovaskulêre siekte (KVS). Plaatjies speel 'n belangrike rol in beide inflammasie en immuun aktivering en met aktivering degranulate en skei plaatjies verskeie inflammatoriese, coagulatory en adhesie molecule af. Geaktiveerde plaatjies druk oppervlak P-selectin (CD62P) is 'n belangrike komponent van die stollings weg en dien as 'n skakel tussen inflammasie en trombose. Geaktiveerde plaatjies is in beide inflammasie en kardiovaskulêre siekte betrokke en is geïdentifiseer as immuun selle wat 'n deurslaggewende rol speel in die patogeen erkenning en modulasie van immuun selle tydens infeksies. Verskeie antivirale en antibakteriese eienskappe van plaatjie alpha korrel inhoud is vasgestel. Plaatjie aggregometry bly die mees gebruikte tegniek om plaatjie funksie te evalueer, alhoewel hierdie tegniek is beperk deur baie pre-analitiese veranderlikes. Plaatjie vloeisitometrie aan die ander kant bied 'n vinnige meting van plaatjie funksie in hul fisiologiese omgewing met 'n minimale artefactual aktivering. Min studies het egter berig op gestandaardiseerde metodes om plaatjie funksie in die konteks van MIV te evalueer. Plaatjie funksie is steeds onduidelik en data oor MIV besmet behandeling naïef individue bly skaars. Die doel van hierdie projek was om die verhouding tussen die plaatjie funksie en immuun aktivering in pasiënte met MIV te ondersoek. Materiaal en metodes Hierdie studie het bestaan uit vyf sub-studies. In die eerste plekis plaatjie indekse en vlakke van plaatjie aktivering bepaal in 'n groep van 330 deelnemers (185 MIV-besmette ARV naïef en 145 onbesmette gesonde kontrole) met behulp van vloeisitometrie en hematologie ontleders. Die verhouding tussen hierdie indekse en merkers van plaatjie aktivering, die siekte se progressive en immuun aktivering is beoordeel. Verder is die vlakke van plaatjie aktivering en samevoeging in 'n groep van 82 deelnemers (41 MIV-besmette (ARV naïef) individue en 41 onbesmette gesonde kontrole) geëvalueer, met behulp van 'n nuwe vol bloed vloeisitometrie gebaseerde funksionele toets. Hierdie basislyn vlakke is dan gekorreleer met merkers van immuun aktivering en die progreessie van die siekte in MIV. In 'n daaropvolgende studie, is plaatjie funksie in 'n groep wat bestaan uit 58 MIV besmet te (ARV naïef) en 38 onbesmette beheer geëvalueer met behulp van vloeisitometrie. Plaatjie reaksie is na stimulasie gemeet met adenosine diphophate (ADP) by konsentrasies bekend omkeer (0.04mM) te oorreed en onomkeerbaar (0.2mm) plaatjie aggregasie. Ten einde plaatjie funksie in MIV te evalueer, is plaatjie reaksie in 'n groep wat bestaan uit 58 MIV-besmette (ARV naïef) en 38 onbesmette kontrole geëvalueer. Die plaatjies is geaktiveer deur gebruik te maak van wisselende konsentrasies van ADP, is aragidoonsuur (AA) en kollageen en plaatjie funksie gemeet met behulp van vloeisitometrie. Vlakke van sirkulerende plaatjie leukosiet gemiddeldes is ook gemeet met behulp van vloeisitometrie in 'n groep wat bestaan uit 35 MIV-positiewe (ARV naïef) individue en 32 onbesmette gesonde kontrole. Assosiasies tussen leukosiet gemiddeldes, immuun aktivering en die progressive van ie siekte in MIV-besmette individue is ook bepaal. Die finale studie het plaatjie-gemiddeldes, plaatjie afgelei mikrodeeltjies en mikrodeeltjies geëvalueer in 'n groep wat bestaan uit 46 MIV besmet (ARV-naïewe) en 40 onbesmette gesonde kontrole. Assosiasies tussen mikrodeeltjies, plaatjie afgelei, plaatjie gemiddeldes en merkers van immuun aktivering en die siekte se progressie is geëvalueer. Resultate MIV-besmette individue het gedaalde gemiddelde plaatjie volume vlakke getoon (HIV gemiddelde 7,91 ± 0,85 8,52 ± 1,12 teen, p <0,0001) wat direk gekorreleer het met CD4-tellings (r = -0,2898, p = 0,0075) en virale (r = 0,2680, p = 0,0177). Plaatjie verspreiding breedte vlakke het direk gekorreleer met (r = 0,3455, p = 0,0362) met 'n aktiewe koagulasie en omgekeerd gekorreleer (r = -0,3666, p = 0,0463) met plaatjie aggregasie. MIV-besmette individue het verhoogde vlakke van plaatjie aktivering getoon (% CD62P mediaan 11,33 [5,96-29,36] teen kontrole groep 2,48 [1,56-6,04], p = 0,0001). In MIV, was plaatjie funksie behou en plaatjies het 'n verhoogde reaksie op submaksimale konsentrasies van endogene agoniste getoon. MIVbesmette individue het verhoogde vlakke van sirkuleer plaatjie monosiet-gemiddeldes gedemonstreer (25.26 [16,16-32,28] teen kontrole groep 14,12 [8,36-18,83], p = 0,0001) wat direk gekorreleer het met merkers van immuun aktivering; % CD38 / 8 (r = 0,54624, p = 0,0155), virale lading (r = 0,633, p <0,009). Verder rapporteer ons op verhoogde vlakke van sirkulerende mikrodeeltjies (mediaan% LP 1.7 [0,95-2,83] teen kontrole groep 1,12 [0,63-1,57], p = 0,0160); PMPs (mediaan% PMPs 26,64 [11,33-36,62] teen kontrole groep 20,02 [18,08-26,08], p = 0,0133); geaktiveer PMPs (mediaan CD62P MFI 3,81 [3,46-4,54] teen kontrole groep 3,41 [3,16- 3,6], p = 0,0037) en plaatjie gemiddeldes (Mediaan% CD62P 14,10 [5,49-39,94] teen 0.17 [0,10- 10,99], p= 0.0097) in MIV besmet asimptomatiese individue. Gevolgtrekking Hierdie studie ondersteun die potensiële gebruik van die MPV en PDW as waardevolle geredelik waardevolle merkers van plaatjie aktivering en immuun aktivering in MIV. Ons het ook getoon verhoogde vlakke van geaktiveer de plaatjies in MIV-besmette individue getoon wat hyper reageer op endogene agoniste was in 'n konsentrasie-afhanklike wyse. Plaatjie vloeisitometrie is 'n vinnige en waardevolle tegniek in die evaluering van plaatjie funksie in MIV. Die meting van plaatjie funksie gebruik vloei cytometry maak die evaluering van plaatjie sein paaie wat in MIVgeïnfekteerde individue verander moontlik. Laastens het ons beskryf 'n hele bloed vloeisitometrie gebaseer de toets vir die evaluering van sirkulerende mikrodeeltjies, plaatjie afgelei mikrodeeltjies en vlakke van geaktiveer plaatjies en gemiddeldes wat lyk soos die in vivo fisiologiese omgewing van MP's. Na die beste van ons kennis, is hierdie studie die eerste om te rapporteer oor 'n nuwe benadering in die evaluering van plaatjie funksie in MIV met behulp van 'n reeks van new hele bloed vloeisitometrie gebaseer de plaatjie toetse. Daarbenewens is minimale werk voorheen uitgevoer op die plaatjie funksie in die konteks van MIV-infeksie; en veral in 'n groep van asimptomatiese, onbehandelde pasiënte soos vir hierdie studie. Hierdie projek het bewyse bygevoeg tot die teorie dat plaatjies, in MIV, kan 'n skakel wees tussen die aktiewe inflammatoriese reaksie en die toename in die aantal trombotische en kardiovaskulêre siekte waargeneem in pasiënte wat met hierdie siekte saamleef.

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