Projection area of human umbilical artery and vein endothelial cells grown to confluence. Passage 2–4 HUAECs and HUVECs were grown to confluence and fixed. CD31 was localized by indirect immunofluorescence, and DNA was labeled with 4',6-diamidino-2-phenylindole dihydrochloride. The projection area of 50 cells was calculated (see Methods). A and B are representative merged micrographs of HUAECs from a <2.8 kg or >3.5 kg birth weight individual, respectively, showing the presence of CD31 in the cell perimeter, as well as the cell nucleus. C, projection area of HUAECs and HUVECs from individuals of <2.8 kg (n = 11 and n = 6, respectively, black bars) or >3.5 kg (n = 11 and n = 6, respectively, white bars) birth weight. Difference was statistically significant (p < 0.05) for the area of HUAECs from both groups. Bar in A and B, 50 μm.