Three typical examples of how activated platelets can mediate cell–cell interactions and affect innate immune responses. (A) Platelet Toll-like receptor (TLR) expression enables activated platelets to bind and capture bacteria. Subsequently, the platelets may directly kill the bacteria by producing thrombocidins or by aggregating around the bacteria and “trapping” them for elimination by professional phagocytes. (B) It is now clear that platelets can also heterotypically interact with a wide variety of cells, including leukocytes. Activated platelets promote neutrophil tethering and activation through the expression of selectins, CD154 (also known as CD40L), and inflammatory cytokines and chemokines. (C) Similarly, activated platelets can promote the activation of monocytes and dendritic cells (DCs), particularly through CD40–CD154 interactions. This leads to increased antigen presentation to T cells and enhances adaptive immune responses. MHC, major histocompatibility complex; TCR, T-cell receptor. Reprinted from Semple et al,²  with permission from Macmillan Publishers Ltd.