Monoclonal antibodies (MAbs) were raised against the outer membrane (OM)
antigens of Salmonella typhimurium.
Enzyme-linked
immunosorbent assays and Western immunoblots indicated that 10 MAbs in the panel were specific for surface
epitopes, and 10 recognized buried
epitopes of OmpC or OmpD
porins; three MAbs reacted with smooth lipo-
polysaccharide (LPS), two bound rough LPS, and the remaining three MAbs apparently reacted with a
porin-LPS complex. We screened these MAbs and immune polyclonal sera in CAF1 (Ity) mice for their relative immunoprotective potential against a challenge with 10 to 500 LD50 of the virulent S. typhimurium LT-2 strain WB600, or against two LD50 of purified OM from this organism. Polyclonal sera that contained high titers of
antibodies to
porin monomers and trimers, and LPS, provided significant protection (33 to 100% survivors). Antiporin MAbs, when administered individually, did not protect or prolong the survival of mice. A mixture of MAbs with specificity for the surface, but not buried
epitopes of
porins, prolonged the survival of mice against
endotoxemia, but none provided significant protection against mouse
typhoid. MAbs specific for smooth (but not rough) LPS on the other hand, conferred significant protection against
endotoxemia and mouse
typhoid. Finally, MAbs that presumably recognized
epitopes present in
porin-LPS complexes, were also protective against
endotoxemia and mouse
typhoid. These results support the role of
antibodies to LPS O-chains,
porin-LPS complexes, and to a lesser degree, native
porins in acquired resistance to
infection by S. typhimurium.