Rickettsia rickettsii, the etiologic agent of
Rocky Mountain spotted fever, purified from infected L-929 cells by density gradient banding were extrinsically radioiodinated with
lactoperoxidase. Immunodominant 125I-labeled
antigens were identified by radioimmunoprecipitation of
detergent-solubilized
antigens with
protein A-Sepharose and anti-R. rickettsii sera collected 0, 3, 7, 11, 32, and 163 days after
infection of guinea pigs. The average
fever greater than or equal to 40 degrees C was detected by days 3 and 4 after
infection with 6 X 10(7) and 6 X 10(6) PFU, respectively. By microagglutination and
complement fixation assays, anti-R. rickettsii
antibodies were detected as early as day 3 after
infection, with titers increasing markedly between days 7 and 163. Convalescent sera, collected on day 163, from infected guinea pigs were used to identify seven 125I-labeled
antigens with apparent molecular sizes of 186,000 (I), 145,000 (II), 49,000 (III), 32,000 (IV), 27,500 (V), 17,500 (VI), and 16,500 (VII) daltons. Differences in antibody reactivity and specificity against the seven
antigens were demonstrated with serially obtained sera. Sera from a guinea pig infected with 6 X 10(7) PFU exhibited antibody-
antigen interactions with all seven 125I-labeled
antigens by day 7, whereas the same antibody activity required 32 days for an animal infected with 6 X 10(6) PFU. Prominent antibody activities toward
proteins II and IV were demonstrated both early and late after
infection. The fluids obtained from infected L-929 cells contained three soluble
antigens which were detected with the 11-, 32-, and 163-day sera by an immunodiffusion assay. The soluble and 125I-labeled
antigens of R. rickettsii identified in this study may be important candidates for
vaccines against
Rocky Mountain spotted fever.