Live Bartonella henselae enhances endothelial cell proliferation without direct contact

The proliferation of human umbilical vein endothelial cells (HUVECs) cocult ivated with live B. henselae was enhanced in a bacterial dose-dependent man ner, and the stimulatory effect was specific to vascular endothelial cells. The inactivation of B. henselae by UV or heat treatment abolished its stim ulatory activity, suggesting that live bacteria is necessary for the growth stimulation effect. To investigate the role of direct contact, live B. hen selae were separated from HUVECs by a filter membrane (Millicell-CM insert) . Even under this condition, an enhanced proliferation of HUVECs was observ ed. However, no morphological changes in the HUVECs were apparent compared to the B. henselae-infected cells. Furthermore, we isolated a nonpiliated s train of B. henselae that is unable to attach to and enter into endothelial cells. The nonpiliated strain possessed the ability to stimulate the proli feration of cocultivated HUVECs the same as the piliated strain. Moreover, the culture supernatants of B. henselae were also able to induce HUVEC prol iferation. Our results indicate that the stimulation of HUVEC proliferation by B. henselae is mediated by soluble factor(s) secreted from the bacteria . (C) 1999 Academic Press.