TABLE 1.

Infection of different types of endothelial cells with Rickettsia rickettsii^a

Cell type	% of infected cells	Avg no. of rickettsiae/infected cell
HMECs	88	4.7
HPAECs	91	7.5
HPMECs	86	4.3
HUVECs	86	5.4
SV-HCECs	90	4.5

^aEndothelial cells of different origin were cultured on sterile plastic coverslips to 80 to 90% confluence and infected with approximately 6 × 10⁴ PFU of R. rickettsii in antibiotic-free culture medium. At 6 h, cells were gently washed, fixed in a 3.7% formaldehyde solution in PBS and stained by fluorescence with anti-R. rickettsii antiserum. For each condition, a minimum of 100 cells in randomly selected fields were scored for the number of R. rickettsii organisms per cell (29).