Platelets can modulate lymphatic endothelial cell behavior. VEGF-C–driven migration of LECs in the absence or presence of washed platelets from Clec1b^fl/fl or Clec1b^fl/flPF4-Cre (A; n = 4) and Syk^fl/fl or Syk^fl/flPF4-Cre (C; n = 3) mice was assessed with the transfilter assay. The percentage of LECs that migrated through the filter was reduced significantly when platelets from Clec1b^fl/fl or Syk^fl/fl mice were applied to the LECs. Application of platelets from Clec1b^fl/flPF4-Cre or Syk^fl/flPF4-Cre mice significantly increased the amount of migration in comparison to the migration seen in the presence of platelets from Clec1b^fl/fl or Syk^fl/fl mice. Cross-linking of podoplanin (E) with the use of the Ab NZ-1.3 with a cross-linking secondary IgG2a resulted in a significant decrease in VEGF-C–mediated migration, whereas application of irrelevant IgG or the Ab without the cross-linking secondary showed no effect. Data represent mean values from ≥ 3 independent experiments performed in duplicate (mean ± SD; **P < .006, *P < .02). Network formation by LECs on Matrigel in the absence or presence of washed platelets from Clec1b^fl/fl or Clec1b^fl/flPF4-Cre (B) Syk^fl/fl or Syk^fl/flPF4-Cre (D) and Clec1b^fl/fl platelet releasate (F) was assessed by seeding LECs in Matrigel-coated 12-well plates. The complexity of networks formed by LECs were reduced significantly when platelets from Clec1b^fl/fl or Syk^fl/fl mice were applied, whereas application of platelets from Clec1b^fl/flPF4-Cre or Syk^fl/flPF4-Cre mice only partially reduced network complexity, and platelet releasate showed no significant effects on network formation. Data represent mean values from 3 independent experiments performed in duplicate (mean ± SD; **P < .005, *P < .05). (G) Representative pictures of networks analyzed for the network-forming assay after application and incubation with either buffer (left) or platelets from Clec1b^fl/fl (middle) or Clec1b^fl/flPF4-Cre (right) mice. Scale bars = 100 μm.