Analysis of T-cell-dependent and -independent antigens of Rickettsia conorii with monoclonal antibodies

Four monoclonal antibodies from euthymic mice and two monoclonal antibodies from athymic mice were directed against antigens of Rickettsia conorii, as shown by both indirect immunofluorescence and an enzyme immunoassay. There was extensive cross-reactivity with other spotted fever group rickettsiae. Euthymic monoclonal antibodies 3-2 and 9-2 (immunoglobulin G2a [IgG2a]) and 27-10 (IgG1) distinctly outlined the acetone-fixed rickettsial surface, as determined by indirect immunofluorescence; only monoclonal antibody 3-2 reacted with the intact rickettsial surface, as determined by colloidal gold-protein A negative-stain electron microscopy. Athymic monoclonal antibodies 32-2 and 35-3 (IgM) and euthymic monoclonal antibody 31-15 (IgG3) all demonstrated an irregular, extrarickettsial morphology, as determined by immunofluorescence, and ultrastructural cell wall blebs that were readily shed from the rickettsial surface. Monoclonal antibody 3-2, the only antibody to confer protection in lethally challenged mice, reacted with a high-molecular-weight protein in Western immunoblots. Monoclonal antibodies 31-15, 32-2, and 35-3 reacted with a 'ladder' of proteinase K-resistant, lipopolysaccharide like antigens. None of the monoclonal antibodies stabilized the ultrastructural rickettsial slime layer, but both athymic and euthymic polyclonal antibodies to R. conorii did. This is, to the best of our knowledge, the first report of the production of monoclonal antibodies to R. conorii and their use for antigenic analysis.