Properties of a rat monoclonal antibody reactive with both the mannan of Candida species and the O-antigen 6,7 polysaccharide of serogroup C1 salmonellae.

Monoclonal antibody MASC1-MR9 of isotype immunoglobulin M was generated in LOU/C rats by immunization with heat-killed Salmonella thompson (serogroup C1, O-antigen 6,7 lipopolysaccharide) bacteria which had been further enriched for O-antigen by coating with homologous lipopolysaccharide. Eight monoclonal antibodies were selected by screening against the lipopolysaccharide of S. thompson. In a subsequent test against Candida mannan, only one antibody, MASC1-MR9, was reactive. Immunofluorescence microscopy of various yeasts and bacteria with MASC1-MR9 showed that this antibody bound to the surfaces of 142 of 148 Candida strains of 10 different species tested but failed to bind to the surface of Saccharomyces cerevisiae. The Candida strains which failed to bind MASC1-MR9 were all five strains of Candida krusei and the single strain of Candida utilis tested. Several (11 of 33) Salmonella strains belonging to serogroup C1 reacted with this antibody, as expected; however, 1 of 11 strains of Morganella morganii and 4 of 64 strains of Escherichia coli were also reactive. Serum-free supernatants of MASC1-MR9 agglutinated S. thompson, one strain of Salmonella choleraesuis, and 109 of 110 Candida strains tested. The immunochemical properties of MASC1-MR9 as studied by enzyme-linked immunosorbent inhibition assays show that it recognizes an epitope present in the mannan of Candida species as well as in the O-6,7 antigen of Salmonella species.