OmpA+, OmpA−, pOmpA+ or heat-killed ES (HK OmpA+ ES) or LPS were incubated with DCs for 24 h and 48h. In some experiments, ES were pretreated with 20 µg ml−1 chloramphenicol for 1 h at 37°C, washed and adjusted the OD600 to obtain 107 cfu ml−1 , and then added at an MOI of 10 to DCs (ES+CM 0 h). In addition, chloramphenicol was added to bacteria-DC co-culture 6 h post-infection (ES+CM 6 h). DCs were then washed, stained with antibodies to CD40 (A), HLA-DR (B) and CD86 (C), fixed and analyzed by flow cytometry. In separate experiments, DCs were first stimulated with LPS or maturation medium (MM) for 24 h and then infected with OmpA+ ES for an additional 24 h. DCs were then washed and the expression of CD40 (D), HLA-DR (E), and CD86 (F) was analyzed by flow cytometry. The data represent geometric mean fluorescence intensity (MFI) of logarithmic data subtracted from isotype-matched controls. DCs infected with ES, LPS or MM were added to naïve T cells to examine the antigen presentation capacity of DCs as described in materials and methods (G). The error bars represent standard deviations from the means of triplicate samples. The results are representative of three independent experiments. The inhibition of cell surface marker expression or antigen presentation was significantly reduced in comparison to LPS infected DCs, *p<0.001 by two tailed t test.