FIG. 2.

Effects of passage history on the stimulation of neutrophil and monocyte transendothelial migration by C. pneumoniae. HUVEC monolayers cultured in transwells were inoculated with LP or HP C. pneumoniae A-03, PS-32, or BR-393 at a multiplicity of infection of 1:1. Equivalent inoculum concentrations of each isolate were inactivated by heat or UV light before infection. LP isolates were passaged <15 times and HP isolates were passaged >40 times in HEp-2 cell cultures prior infection of HUVEC. Levels of neutrophil (A) and monocyte (B) transendothelial migration were determined following 24 h of incubation (see Materials and Methods). Bars indicate means ± standard errors of the means of three separate experiments. In each experiment, triplicate wells were assayed separately for each experimental variable. Data have been normalized to mock-infected levels of neutrophil and monocyte migration (3.9 ± 0.7 and 3.3 ± 0.8 cells/HPF, respectively). Levels from uninfected cells were 3.9 ± 1.1 cells/HPF for neutrophils and 3.5 ± 0.9 cells/HPF for monocytes. The response to HUVEC treated with 500 U of TNF-α per ml, as a positive control, increased to 20.6 ± 4.9 cells/HPF for neutrophils and 14.7 ± 1.6 cells/HPF for monocytes. ∗, P < 0.05; ∗∗, P < 0.01; ∗∗∗, P < 0.001.