Fig. 2

a Platelets protect CTCs within circulation. The platelet coat around CTCs physically shields them from NK cell attack. Moreover, platelets can transfer their MHC I molecules onto the membranes of CTCs. This allows CTCs to downregulate expression of their own MHC I molecules, evading T cell recognition without eliciting attack from NK cells through "missing self" recognition. Platelets can also impair NK cell recognition of CTCs via activation of NKG2D receptors. Platelets also promote association with NET to assist CTC distribution and adhesion. Through inducing the RhoA/YAP pathway, platelets promotes CTCs' resistance to apoptosis. b Through CD40/CD154 interaction or release of microparticles, platelets prime endothelid cells for attachment. Platelets promote capture of CTCs by the endothelium and reduce rolling rate. Mediated by integrins platelets-CTC complex adhere to the endothelium. ATP-released platelets interact P2Y2 receptor endothelid cells ceasing opening endothelid bar.