Endothelial tube formation in Matrigel.

(A) Yolk sac–derived endothelial cells were plated in Matrigel and cultured for 60 hours without factor (Ai) or with CD4-Fc (Aii) or ALCAM-Fc (Aiii). Scale bar, 50 μm. (B) The number of tubes formed in Matrigel was counted in each field under a microscope, and mean ± SD was obtained from quadriplicate wells. *P < .05.