Supernatants from stored platelet concentrates modulate the inflammatory response in platelet-depleted blood ex vivo

Introduction Platelets contain a wide range of bioactive mediators, many of which accumulate during storage of platelet concentrates and have immunomodulatory properties. Our objective was to investigate how mediators derived from stored platelet concentrates modulate the acute inflammatory response using an ex vivo model. Methods Platelet-depleted whole blood from healthy donors (n=8) was supplemented with pooled platelet concentrate supernatants generated from six platelet concentrates sampled on storage days 1, 3, 5, and 7, and incubated with or without heat-inactivated Escherichia coli for four hours at 37 °C. Inflammatory responses were assessed by measuring complement activation, platelet-derived mediators, and cytokines. Results In the absence of E. coli , addition of platelet concentrate supernatants increased the levels of 24 of 32 measured inflammatory mediators. In contrast, under E. coli -stimulated conditions, the supernatants increased 10 markers and attenuated 14 markers, including the key pro-inflammatory cytokines IL-1β, IL-6, and TNF. The attenuation of these cytokines ranged from 25-43%, whereas several other mediators were unchanged or increased. The majority of biomarkers showed limited differences across the investigated storage time points. Conclusions Our findings demonstrate that soluble factors released from platelet concentrates can modulate inflammatory responses in platelet-depleted blood in an ex vivo setting, with context-dependent, bidirectional, and selective immunomodulatory effects.