FIG. 2.

Secretion of IpaC is increased in S. flexneri expressing mutant forms of ipaD. An ELISA was used to allow initial detection of IpaC quantities in the culture supernatants of S. flexneri strain SF622 expressing ipaD harboring different deletions. The primary antibody used here was a mouse monoclonal antibody that recognizes an epitope precisely mapped to the central hydrophilic region of IpaC (37). All analyses were performed in triplicate and are presented as an average ± standard deviation (n = 5) from one of two nearly equal experiments in which the upper limit with respect to linearity for the IpaC protein is approached but not exceeded. On the basis of rough standard curves with purified recombinant IpaC, all of the values observed for the detection of IpaC are within the linear range of detection by this ELISA system, although the higher IpaC values are near the upper range of linear detection. The asterisks indicate P values (Student t test) of ≤0.10.