Human response to Escherichia coli O157 : H7 infection: Antibodies to secreted virulence factors

Vaccination has been proposed for the prevention of disease due to enterohe morrhagic Escherichia coli (EHEC), but the immune response following human infection, including the choice of potential antigens, has not been well ch aracterized. To study this, sera were obtained from five pediatric patients with acute diarrhea caused by E. coli O157:117 0, 8, and 60 days after hos pitalization. These sera were used to examine the immune response to four d ifferent EHEC virulence factors: Tir (translocated intimin receptor, which is inserted into the host cell membrane), intimin (bacterial outer membrane protein which binds to Tir), EspA (secreted protein which forms filamentou s structures on EHEC surface), and EspB (inserted into the host membrane an d cytoplasm). The response to O157:H7 lipopolysaccharide was also examined. Sera were assayed against purified recombinant proteins using immunoblot a nalysis and by enzyme-linked immunosorbent assay to determine the sera's ti ters to each of the antigens in all patients, We found that there was littl e reaction to EspA EspB, and intimin in the acute-phase sera, although ther e was some reactivity to Tir. By day 8, titers of antibody to all four viru lence factors were present in all patients, with a very strong response aga inst Tir (up to a titer of 1:256,000), especially in hemolytic-uremic syndr ome patients, and lesser strong responses to the other three antigens. The titer to the antigens 60 days after hospitalization was decreased but was s till highest for Tir. These results suggest that there is a strong immune r esponse to Tir, and to a lesser extent to the other three virulence factors , following EHEC disease, indicating that these bacterial molecules are pot ential vaccine candidates for preventing EHEC disease. They also suggest th at bacterial virulence factors that are inserted into host cells during inf ection by type III secretion systems (Tir or EspB) are still recognized by the host immune response.