PB0745 - Effect of platelets on trained immunity in monocytes: a proof of concept study

Background: Platelets induce and regulate inflammation in innate immune cells. Atherogenic particles such as oxidized low-density lipoprotein (ox-LDL), as well as other compounds such as β-glucan, induce a long-term proinflammatory phenotype in monocytes. This mechanism is called ‘trained immunity’ and contributes to chronic low-grade inflammation in atherosclerosis. The effects of platelets on trained immunity have not yet been investigated, although their pleiotropic function make platelets a potential important player in the link between inflammation and atherosclerosis.

Aims: To investigate the effect of platelets on trained immunity in vitro.

Methods: Primary human monocytes, platelet-depleted human monocytes, and platelet-depleted human monocytes with replenishment of homologous platelets, were trained via pre-exposure for 24 hours to ox-LDL (10 µg/ml), β-glucan (10 µg/ml), or medium only. After washing and resting for 6 days, the cells were re-stimulated for 24 hours with lipopolysaccharide (LPS). As a functional readout of trained immunity, production of interleukin-6 (IL-6) and tumor necrosis factor (TNF) was measured in the supernatants with ELISA.

Results: In β-glucan-trained monocytes, platelet depletion resulted in a more variable TNF and IL6 production after LPS restimulation, compared with standard monocytes (Figure 1 and Figure 2). Replenishment of homologous platelets resulted in inhibition of the training effect reflected by lower cytokine responses after LPS-restimulation (p=0.0449) (Figure 1). The same trend was observed for ox-LDL trained cells, albeit to a lesser extent.

Conclusion(s): After LPS restimulation, β-glucan-trained platelet-depleted human monocytes showed a more variable cytokine response than standard β-glucan-trained monocytes, whereas replenishing of platelets resulted in inhibition of β-glucan training. This may suggest an immunosuppressive function of platelets in monocyte training. We are currently further exploring the mechanism of this effect.