Purified radioactive rickettsiae were obtained from irradiated and cycloheximide-inhibited L cells, and their proteins were analyzed by polyacrylamide gel electrophoresis. Rickettsial species could be distinguished by comparing the relative mobilities of constituent proteins after migration of two differentially labeled preparations in a single gel. Distinct differences were observed in gel patterns of rickettsiae from the typhus and spotted fever groups, as well as with different species within a group. Rickettsial organisms causing murine and epidemic typhus were clearly distinguished, as were the causative agents of boutonneuse fever and rickettsialpox. The use of both internal and external molecular weight standards allowed molecular weight estimates for 19 proteins from both Rickettsia prowazekii and Rickettsia conorii. A flexible system for designating rickettsial proteins is proposed that lends itself to modification as more detailed analysis progresses.

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Six proteins, previously established as major constituents of intact organisms were identified in cell envelopes obtained from intrinsically radiolabeled Rickettsia prowazekii. Extrinsic radioiodination of intact organisms conducted at 0.5 !LM iodide indicated that protein 4 was the most peripheral, although protein 1 also had reactive groups exposed on the surface of the organisms. A 10-fold increase in iodide concentration resulted in labeling of protein 2, and at 50 ,uM iodide, all six major proteins were radiolabeled. Similar selective labeling was not achieved with R. conorii. Analysis of both typhus and spotted fever group organisms radiolabeled with galactose suggested that carbohydrate was associated with proteins 1, 3, and 4. Typhus soluble antigen included all major proteins except protein 2, which remained attached to particulate rickettsiae after ether extraction. Protein 4 appeared to be prominent in the surface topography of R. prowazekii, was a component of soluble antigen and may have an important role in rickettsiae-host interactions.

The requirement of thymus-dependent lymphocytes for antibody production to Rickettsia tsutsugamushi, Rickettsia akari, Rickettsia conorii, and Rickettsia typhi was investigated by comparing antibody production in athymic (nu/nu) or thymus-bearing BALB/c mice. Athymic BALB/c mice produced antibody after infection with R. akari, R. conorii, and R. typhi as measured by indirect fluorescent antibody titration or radioimmunoassay. Antibody production in these mice was as great or greater than in the thymus-bearing mice and demonstrated similar kinetics. In contrast, athymic BALB/c mice infected either intraperitoneal

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