O-Specific polysaccharide conjugate vaccine-induced IgG antibodies prevent invasion of Shigella into Caco-2 cells and may be curative

doi:10.1073/pnas.0610833104

O-Specific polysaccharide conjugate vaccine-induced IgG antibodies prevent invasion of Shigella into Caco-2 cells and may be curative

Departments of *Gastroenterology,
^¶Bacteriology, and
^‖Pathology and
^§§The Samuel Jared Kushnick Pediatric Immunology Laboratory, The Edmond and Lily Safra Children's Hospital, Chaim Sheba Medical Center, Tel Hashomer 52621, Israel;
^§Department of Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel;
**Schneider Children's Medical Center of Israel, Petach Tiqva 49202, Israel;
^††Laboratory of Developmental and Molecular Immunity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892; and
^†The Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel

Contributed by John Robbins, December 14, 2006 (received for review June 26, 2006)

Abstract

The O-specific polysaccharide (O-SP) domain of Shigella LPS is both an essential virulence factor and a protective antigen for this genus. A critical level of serum IgG anti-O-SP was shown to confer immunity to shigellosis, likely by complement-mediated bacteriolysis of the inoculum. Conjugate Shigella O-SP vaccines were shown to be safe and immunogenic in children, and, in a preliminary study, Shigella sonnei vaccine was protective in young adults. Characteristic of shigellosis is bacterial invasion of intestinal cells. Incubation of shigellae with postimmunization but not preimmunization sera of children vaccinated with S. sonnei or Shigella flexneri 2a O-SP conjugate vaccines inhibited in a type-specific and dose-dependent manner in vitro invasion of intestinal epithelial cells (Caco-2) and the infection-associated increases in IL-1β and IL-8 mRNA and extracellular cytokine levels. Pretreatment of these sera or of Caco-2 cells with O-SP abrogated these effects also in a type-specific and dose-dependent manner. Confocal microscopy demonstrated antibody-specific inhibition of bacterial adhesion to HeLa cells. These protective effects were duplicated by IgG purified from these sera. These results suggest a dual role for IgG anti-O-SP. In addition to lysis of the inoculum in immune individuals, the newly synthesized IgG anti-O-SP in patients may terminate an established infection by inhibiting shigellae released from epithelial cells from invading new ones. A critical level of IgG anti-O-SP could, therefore, have a protective as well as a curative role in shigellosis.

vaccination

Footnotes

^‡To whom correspondence may be sent at the * address. E-mail: ychowers{at}post.tau.ac.il
^‡‡To whom correspondence may be sent. E-mail: robbinsjo{at}mail.nih.gov
Author contributions: Y.C., R.S., and J.H.P. designed research; J.K. performed research; N.K., S.B.-M., S.A., R.S., and J.H.P. contributed new reagents/analytic tools; Y.C., I.B., R.S., J.R., and J.H.P. analyzed data; and Y.C., S.A., R.S., J.R., and J.H.P. wrote the paper.
↵ ^¶¶Deceased June 3, 2006.
The authors declare no conflict of interest.
Abbreviations:

O-SP,

O-specific polysaccharide;

HBI,

heart–brain infusion.