ABSTRACT
BackgroundPlatelets have recently been recognized as immune cells. Platelets first contact invading pathogens and then induce immune reactions in cooperation with white blood cells. Platelet polyphosphate (polyP), which is classically recognized as a thrombotic and hemostatic biomolecule, has recently attracted attention as a cytokine that modulates inflammation and is involved in intercellular communication between platelets and major immune cells. ObjectiveTo determine the involvement of polyP in SARS-Cov-2-mRNA vaccine-induced immune responses, this pilot study examined the effects of mRNA vaccines on platelet polyP levels. MethodsBefore and after vaccination (BNT162b2), blood samples were obtained from healthy, non-smoking individuals (relatively older male group, n=6 vs. younger female group, n=23), who did not have systemic diseases that required continuous treatment. Washed platelets were prepared and subjected to a fluorometric determination of platelet polyP levels using 4,6-diamidino-2-phenylindole. The side effects of vaccination were recorded as scores. ResultsCompared with the male group, platelet polyP levels decreased in the relatively younger female group after the initial dose, while the side effect score increased in the female group after the second dose. Moderate correlation coefficients were observed between the reduction in polyP levels and the side effect scores or the original polyP levels. ConclusionsDespite being a pilot study using a small sample size, this study suggests the possibility that platelet polyP may suppress the side effects induced by the mRNA vaccines after the initial dose, but not the second dose, in relatively young female subjects who generally have high immune responsiveness. EssentialsO_LIThe COVID-19 mRNA vaccines (BNT162b2) reduced platelet polyP levels after the initial dose, but not after the 2nd dose, in relatively younger female subjects. C_LIO_LIRelatively older male subjects did not respond to the vaccination by reducing platelet polyP. C_LIO_LIThese findings suggest that platelets release polyP to suppress vaccine-induced reactions, for example, inflammation, which is usually recognized as a side effect. C_LIO_LIHowever, such suppression could be observed in subjects with higher immune responses, generally in relatively younger female subjects. C_LI
