CHARACTERIZATION OF MONOCLONAL-ANTIBODIES PROTECTING MICE AGAINST RICKETTSIA-RICKETTSII

Hybridomas producing monoclonal antibodies to R. rickettsii were prepared from mice to investigate the function of rickettsial antigens. Of the 31 reactive hybridoma lines thus far tested for Ig subclasses, 11 belonged to the IgG2A subclass, 9 to the IgG2B subclass and 7 to the IgG3 subclass; 4 did not react with any of the isotyping sera. Five of the antibodies recognized epitopes present on molecules that were presumed to be polysaccharide and heterogeneous in MW. Twenty monoclonal antibodies reacted with a 170,000-dalton antigen and 6 precipitated the 133,000 and 32,000-dalton polypeptides. Only those antibodies to the 170,000- and 133,000-dalton antigens protected mice from challenge with R. rickettsii. Antibodies to these same antigens were detected in sera from patients convalescing from Rocky Mountain spotted fever. All monoclonal antibodies reacted with antigens apparently located on the rickettsial surface. The protective activity of these antibodies was not correlated with their reactivity in complement fixation, enzyme-linked immunosorbent assay and immunofluorescence tests.