Figure 2. Contribution of platelet–leukocyte interactions to inflammatory-immune responses.

Platelets are activated at the site of endothelial damage or in the microcirculation of infected/inflamed tissue. Activated platelets bind leukocytes to form heterotypic complexes, and communicate signals that result in a variety of specific responses. Platelets mediate the recruitment of leukocytes at the site of atherosclerosis or thrombus formation, as well as in inflamed tissue. In some cases, these interactions mediate platelet–leukocyte co-migration across the mucosal epithelium. In this way, platelets contribute to the promotion of inflammatory reactions, which when not controlled, can exacerbate tissue damage. Platelet might support lymphocyte homing in peripheral lymph nodes, stimulate isotype switching and production of IgG by B lymphocytes, and might help lymphocyte responses to viruses and neutrophil response to bacteria. In this way, platelets contribute to host defense.