Monoclonal immunoglobulin A prevents adherence and invasion of polarized epithelial cell monolayers by Salmonella typhimurium.
OBJECTIVE
Invasion of the intestinal epithelium is considered a critical step in Salmonella pathogenesis. Infection by Salmonella of cultured monolayers of polarized Madin-Darby canine kidney (MDCK) cells has been established as a simple in vitro system that mimics the invasion of intestinal enterocytes in vivo. This study analyzes the protective role of secretory immunoglobulin (Ig) A antibodies against epithelial invasion.


METHODS
Salmonella typhimurium was applied to MDCK cell monolayers in the presence or absence of a monoclonal, polymeric IgA antibody (Sal4) directed against an antigenic determinant exposed on the surface of wild-type S. typhimurium.


RESULTS
In the presence of Sal4 IgA, confluent monolayers of MDCK cells were protected against apical invasion by wild-type S. typhimurium but not against a mutant strain that lacks the Sal4 epitope. Protection was Sal4-specific, dependent on the concentration of Sal4 in the apical medium, and occurred at IgA concentrations at which agglutination of IgA-bacterial complexes was observed. When MDCK cell monolayers were formaldehyde-fixed before incubation with Salmonella to prevent bacterial invasion, adhesion of Salmonella occurred in the absence of IgA and in the presence of control IgA but not in the presence of Sal4 IgA.


CONCLUSIONS
IgA alone can prevent bacterial adherence and invasion of epithelial cells in the absence of other immune or nonimmune protective mechanisms.
Michetti
P
P
Division of Gastroenterology, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
Porta
N
N
Mahan
M J
MJ
Slauch
J M
JM
Mekalanos
J J
JJ
Blum
A L
AL
Kraehenbuhl
J P
JP
Neutra
M R
MR
D000371:Agglutination; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D001422:Bacterial Adhesion / Q000187:drug effects*; D016764:Cell Polarity; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells; D004848:Epithelium / Q000382:microbiology; D007070:Immunoglobulin A / Q000494:pharmacology*; D007668:Kidney / Q000166:cytology / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000276:immunology* / Q000502:physiology
D000911:Antibodies, Monoclonal; D007070:Immunoglobulin A