The conserved cysteines and the first 39 residues of the N-terminal extension of IglG are required for IglG function in LVS.

LDH release (A) and TNF-α secretion (B) from F. tularensis LVS-infected J774 cells. (A) Culture supernatants of infected J774 cells were assayed for LDH activity at 0, 24 and 48 h and the activity was expressed as a percentage of the level of non-infected lysed cells (positive lysis control). Values of triplicate wells (means +/- SD) from one representative experiment of two are shown. The asterisks indicate that the cytopathogenicity levels were different from those of LVS-infected cells at a given time point as determined by a 2-sided t-test with equal variance (*, P ≤ 0.05; ***, P ≤ 0.001). (B) J774 cells left uninfected or infected with F. tularensis at an MOI of 500 for 2 h, were washed and subsequently incubated in the presence of E. coli-derived LPS (50 ng/ml) for an additional 2 h. The average TNF-α secretion (%) compared to LVS, which was set as 100%, and the SD of quadruple samples (n = 4) from one representative experiment out of two is shown. The asterisks indicate that the cytokine levels were significantly different than those of LVS-infected cells as determined by a 2-sided t-test with equal variance (**, P ≤ 0.001; ***, P ≤ 0.001).