A panel of 14
monoclonal antibodies with specificity for the O-antigenic
polysaccharide chain of the
lipopolysaccharide of the cell envelope of Salmonella typhimurium was established. The specificity of each antibody clone was determined against a set of Salmonella saccharide
antigens, natural and synthetic, in passive hemagglutination and
enzyme immunoassays. The
monoclonal antibodies could be classified into at least five different groups: (i) O4
epitope specific, (ii) O4,12 specific, (iii) O4,12(2) specific, (iv) O5 specific, and (v) O12 specific. These specificities correspond to different structural and conformational domains of the
polysaccharide chain, and often extend over more than one repeating unit (tetrasaccharide) of the
polymer. The passive protection afforded by these
antibodies was estimated in an experimental mouse
typhoid model using S. typhimurium SH2201 for intraperitoneal challenge.
Monoclonal antibodies of the
IgG3 isotype were available for four of the
epitope groups and were protective in the following order of activity O4 greater than O4,12 greater than O4,12(2) greater than or equal to O12. The difference between O4 and 012
antibodies was greater than 2500 fold in protective activity.
Antibodies of the
IgM class were highly protective irrespective of being of the O4,12 or O12
epitope specificity. Two
IgA antibodies with O5
epitope specificity were not protective. The results show that both isotype and
epitope specificity can be of importance for the protective ability of
antibodies generated by the host.