[PubMed] [Google Scholar] 18

[PubMed] [Google Scholar] 18. in those with a classical pattern, value <.05 was considered statistically significant. 3.?RESULTS 3.1. Biological and clinical features of HIT patients according to their SRA pattern Among the 81 enrolled HIT patients, 68 had a classical platelet activation pattern in SRA and 13 others exhibited an atypical SRA profile, associated with a significant platelet activation without heparin (serotonin release 30%; Figure?1A,B). In both groups (with classical and atypical SRA pattern), patients were predominantly men, with a median age of 69?years, and treated by heparin in a surgical context in more than 50% of cases (Table?1). There was no difference between the two groups regarding the heparin indication, type of heparin injected, or prior heparin exposure. Open in a separate window FIGURE 1 Two types of SRA pattern were observed in our cohort of HIT patients and underlying mechanisms. (A, B) Platelet activation pattern of HIT patients with a classical SRA profile (no platelet activation without heparin, value(%)30 (44%)5 (38%)Percentage of platelet activation in SRA% without heparin, median [minCmax]10 [0C28]59 [36C92] <.001 % with low UFH concentrations, median Cilomilast (SB-207499) [minCmax]51 [20C100]87 [57C100] <.001 % with high UFH concentrations, median [minCmax]3 [0C24]5 [0C33]NS Open in a separate window Abbreviations: CPB, cardiopulmonary bypass; DIC, disseminated intravascular coagulation; ECMO, extracorporeal membrane oxygenation; HIT, heparin induced thrombocytopenia; LMWH, low molecular weight heparin; NS, nonsignificant; ND, not determined; PC, platelet count; SRA, serotonin release assay; UFH, unfractionated heparin; VTE, venous thromboembolic event. a Calculated on 12 patients. b Calculated on 55 patients. c Calculated on 11 patients. d Circuit (dialysis or ECMO circuits) and catheter thrombosis. Bold values in Tables 1 and 2 indicated p\values with statistical significance (i.e ? 0.05). The baseline PC was similar in both groups, as well as the median PC nadir (49 vs. 38?G/L in classical and atypical SRA groups, respectively, NS) and the time to PC recovery (>150?G/L; median: 5 vs. 6?days, respectively, NS). Importantly, patients with an atypical SRA pattern more frequently developed thrombotic events than those with a classical SRA profile (69% vs. 34%; relative risk?=?2.03; (data not shown). 3.2. Potential contributors to an atypical SRA pattern We then investigated the different parameters that may contribute to platelet activation by HIT antibodies without heparin in functional assays. We first defined these parameters using monoclonal PF4\specific IgG antibodies with a human Fc and then we assessed whether one or more of these mechanisms could explain the platelet activation observed without heparin in our cohort of patients with an atypical SRA profile. 3.2.1. Titers of anti\PF4/H IgG antibodies As demonstrated with the monoclonal antibody 5B9, which mimics classical human HIT Cilomilast (SB-207499) antibodies, 18 a high titer of anti\PF4/H IgG antibodies could explain an atypical SRA profile. Indeed, although 5B9 10 and 20?g/ml activated platelet only in the presence of low heparin concentrations (Figure?1C), 10 times higher concentrations of this antibody (200?g/ml) induced platelet activation without heparin in SRA, with a serotonin release greater than 40% (Figure?1D). In our cohort, different ELISA kits have been used at the time of HIT suspicion, and therefore OD values obtained could not be rigorously compared. For this reason, samples from 34 patients included in the classical SRA group and from 13 with an atypical SRA were Mouse monoclonal to KI67 tested simultaneously using the same ELISA. Interestingly, higher optical densities were measured with an anti\PF4/H IgG ELISA in patients with an atypical SRA profile than in those with a classical platelet activation profile (median OD: 2.5 vs. 1.95, respectively, value(%)17 (66%)11 (52%)NSHeparin indicationVTE treatment, is the concentration of PF4 in the cell environment, as suggested by results obtained with 5B9, 10 and confirmed in this study. However, plasma PF4 concentrations were similar in patients without and with an atypical SRA pattern. Moreover, because these concentrations were below 1?g/ml and lower than those previously defined for allowing HIT antibodies to induce platelet activation without heparin in vitro, 7 , 9 , 10 they unlikely contributed to the atypical pattern of SRA observed in our patients. The third parameter that could affect the biological activity of HIT antibodies is their specificity. More than 20?years ago, we were the first to report that some patients with classical HIT may develop, apart from antibodies to PF4/H complexes, IgG that bind PF4 alone. 23 After affinity purification, we also demonstrated that this difference in specificity may influence Cilomilast (SB-207499) the ability of HIT samples to activate platelets in SRA. 24 Lately, Nguyen et al. demonstrated that some patients with an autoimmune HIT had a subset of.