Platelet activation by bacterial stimuli in hereditary hemorrhagic teleangiectasia

Introduction Patients with hereditary hemorrhagic telangiectasia (HHT) appear to be more susceptible to infections compared to the general population. Because platelets play a crucial role in the activation of the immune response, in this study we investigated whether platelet activation itself is affected by bacterial stimuli.

Methods Whole blood samples from HHT patients and control subjects (no evidence of disease, taking no medication affecting platelets respectively) were incubated with phorbol myristate acetate (PMA) or buffer solution and labeled with fluorescence antibodies against CD14 and CD41. Monocyte-platelet aggregates were assessed by flow cytometry as markers of platelet activation.

Results HHT patients (n=7) had normal to slightly increased platelet (norm 180-380/nl; mean (m) ± standard deviation (SD): 328±73) and leucocyte counts (norm 3.6-9.2/nl; m±SD:6.7±3.3) with normal monocyte percentages (norm 4-14%). The percentage of monocytes with attached platelets was determined and no significant differences were found without bacterial stimulation (p>0.05). Interestingly, when stimulated with PMA the monocyte-platelet aggregate percentage increased significantly (p=0.004; control (m±SD): 10.1±4.3% vs PMA (m ± SD): 20.8±11.2%) in the control group (n=8), while in the HHT group, there was no significant change compared to the unstimulated samples (p>0.05; control 11.6±6.9% vs PMA 19.3±10.8%). However, HHT patients had a higher platelet-leukocyte ratio (p=0.036; m±SD: HHT 56.4±21.9 vs control 37.5±6.4), therefore a stronger tendency to formation of aggregates would rather be expected.

Discussion These results suggest that platelet activation by bacterial stimuli is impaired in HHT, which can have an impact on antibacterial immune responses.

Publication History

Article published online:
12 May 2023