Platelet-activating factor (PAF): signalling and adhesion in cell-cell interactions.

Signalling by PAF is closely linked to adhesive interactions between cells of the inflammatory and vascular systems. It acts as a juxtacrine signal that alters the activity of beta 2 integrins on myeloid leukocytes (Figure 1), and works in concert with P-selectin at the surfaces of endothelial cells (Figure 2 and text). Observations in models of flow and in vivo support the original experiments using cultured endothelium under static conditions that indicated that PAF acts at this vascular interface. P-selectin modifies and integrates signals delivered through the PAF receptor on monocytes (Figure 4). Adhesion via P-selectin and engagement of beta 2 integrins modify signals leading to PAF synthesis (text and Figure 5). The intimate relationship between adhesive events and signalling by PAF may be a critical determinant in its roles in physiologic and pathologic responses.