FIG. 4.

Recombinant GroEL from F. tularensis LVS or Schu S4 does not induce expression of E-selectin by HUVEC. LVS GroEL or Schu S4 GroEL (10 μg/ml) was preincubated for 1 h with 20 μg of polymyxin B/ml. E. coli (Ec) LPS at 0.5 ng/ml was used as a positive control. Prepared samples or culture medium alone (Unstim) was incubated with HUVEC for 4 h at 37°C. The levels of E-selectin were determined by whole-cell ELISA. Bars represent the means ± the SD of four replicate samples. *, Significantly greater than unstimulated samples (P < 0.001). This experiment was repeated two more times, and only once did LVS GroEL slightly but significantly stimulate HUVEC.