1. Enhancement of fibrinolysis by gel-filtered platelets and its quenching by cytochalasin B and GPIIb/IIIa antagonists
Satoru Hoki, Yuko Suzuki, Kazuo Umemura, Tetsumei Urano Pharmacol Rep. 2009 Sep-Oct;61(5):877-84. doi: 10.1016/s1734-1140(09)70144-6.
The effects of gel-filtered platelets on euglobulin clot lysis time (ECLT) were analyzed to elucidate the possible role of platelets in thrombolysis. Gel-filtered platelet-supplemented ECLT (plt-ECLT) was significantly shorter than ECLT without platelets (regular ECLT). Abciximab, anti-glycoprotein IIb/IIIa (GPIIb/IIIa) antibody, and cytochalasin B nullified the enhancement of ECLT by platelets, and increased plt-ECLT beyond regular ECLT. When gel-filtered platelets were used after disruption, ECLT was not shortened but rather became longer than regular ECLT, probably due to natural fibrinolysis inhibitors released from platelets. Therefore, for platelets to enhance fibrinolysis, intact cell structure and cytoskeletal reorganization after thrombin stimulation is required. Various GPIIb/IIIa antagonists prolonged plt-ECLT. The concentrations of GPIIb/IIIa antagonists required to prolong plt-ECLT, were varied. Interestingly, the effects of these antagonists were independent of their ability to inhibit thrombin-induced platelet aggregation, but dependent on their ability to induce clot retraction. T-250, a GPIIb/IIIa antagonist, had the smallest effect on plt-ECLT. These drugs do not affect regular ECLT or tissue plasminogen activator (tPA)-catalyzed Glu-plasminogen activation in the presence of thrombin-activated platelets. Although their overall effect on thrombolysis is inhibitory, platelets could promote fibrinolysis through a GPIIb/IIIa-dependent mechanism.
2. Laboratory evaluation of a new integrative assay to phenotype plasma fibrinolytic system
Marion Bareille, Michael Hardy, Bernard Chatelain, Thomas Lecompte, François Mullier Thromb J. 2022 Dec 5;20(1):73. doi: 10.1186/s12959-022-00435-6.
Background: There is currently no universal and standardized test available to phenotype plasma fibrinolytic system. Aims: Our main aims were to evaluate the performances of the 'global fibrinolysis capacity' assay (GFC) performed with the Lysis Timer® instrument, and to study the influence of some preanalytical conditions. Method: Euglobulin clot lysis time (ECLT) and GFC were performed under several preanalytical conditions. Results: GFC showed satisfactory intra- and inter-run precision. Frozen controls and reagents showed stability over the studied period. There was no statistically significant difference between GFC assessed in plasma samples processed at 4 °C or at 20 °C. GFC assessed with frozen-thawed plasma samples was prolonged when compared to fresh samples (p = 0.014). The centrifugation scheme had no influence on PAI-1 activity levels, GFC and ECLT. Reference interval for GFC ranges from 29.3 (C I90% = 26.9-31.9) to 49.5 (90% CI = 45.9-52.2) minutes. In addition, a preliminary study in 40 healthy volunteers and 43 adult patients referred for investigation of a bleeding disorder was conducted to compare GFC and ECLT assays in their ability to classify samples with shortened or prolonged clot lysis times. Disagreements between ECLT and GFC were observed for 23 samples (out of 83), most of them minor. Conclusion: GFC is suitable and convenient for a broad clinical use and can be performed with frozen-thawed plasma samples. Unlike ECLT, GFC is designed to take into account the balance between inhibitors and activators of the fibrinolytic system and could detect both hypo- and hyperfibrinolytic states. Whether it is as suitable as or even better than ECLT to detect a bleeding tendency due to a hyperactive fibrinolytic system deserves to be properly investigated.
3. Restricted Clonality and Limited Germinal Center Reentry Characterize Memory B Cell Reactivation by Boosting
Luka Mesin, et al. Cell. 2020 Jan 9;180(1):92-106.e11. doi: 10.1016/j.cell.2019.11.032. Epub 2019 Dec 19.
Repeated exposure to pathogens or their antigens triggers anamnestic antibody responses that are higher in magnitude and affinity than the primary response. These involve reengagement of memory B cell (MBC) clones, the diversity and specificity of which determine the breadth and effectiveness of the ensuing antibody response. Using prime-boost models in mice, we find that secondary responses are characterized by a clonality bottleneck that restricts the engagement of the large diversity of MBC clones generated by priming. Rediversification of mutated MBCs is infrequent within secondary germinal centers (GCs), which instead consist predominantly of B cells without prior GC experience or detectable clonal expansion. Few MBC clones, generally derived from higher-affinity germline precursors, account for the majority of secondary antibody responses, while most primary-derived clonal diversity is not reengaged detectably by boosting. Understanding how to counter this bottleneck may improve our ability to elicit antibodies to non-immunodominant epitopes by vaccination.
