Proteins of typhus and spotted fever group rickettsiae

Global Transcriptomic Profiling of Pulmonary Gene Expression in an Experimental Murine Model of Rickettsia conorii Infection

Mediterranean spotted fever develops from an infection with Rickettsia conorii, an obligate intracellular, Gram-negative, endotheliotropic, and tick-transmitted bacterial pathogen, and is an acute, febrile illness that can progress to life-threatening complications if not diagnosed and treated early with effective antibiotics. Despite significant morbidity and mortality, little is known about changes in gene expression that determine the host responses during in vivo infection. We have investigated the transcriptional landscape of host lungs as a prominently affected organ system in an established murine model of infection by RNA-sequencing. Ingenuity pathway analysis resulted in the identification of 1332 differentially expressed genes and 292 upstream regulators. Notably, genes encoding for ubiquitin D, aconitate decarboxylase, antimicrobial peptides, calgranulins, cytokines and chemokines, and guanylate binding proteins were highly up-regulated, whereas those involved in hemoglobin biosynthesis and heme homeostasis were significantly down-regulated. Amongst response regulators, nucleotide-binding oligomerization domain-containing protein 2 and killer cell lectin-like receptors were differentially expressed, and gene clustering revealed eukaryotic initiation factor-2, oxidative phosphorylation, and ubiquitination as the predominantly activated biological pathways. Collectively, this first global transcriptomic profiling has identified R. conorii-induced regulation of novel genes and pathways in the host lungs, further in-depth investigation of which will strengthen our understanding of the pathogenesis of human rickettsioses.

Failure of a heterologous recombinant Sca5/OmpB protein-based vaccine to elicit effective protective immunity against Rickettsia rickettsii infections in C3H/HeN mice

Spotted fever group (SFG) rickettsial species are obligate intracellular tick-borne pathogens that are responsible for important human diseases. Previous reports have demonstrated the feasibility of using recombinant surface cell antigen Sca5/OmpB to elicit protective immunity against homologous challenges using murine models of Mediterranean spotted fever and Rocky Mountain spotted fever. In addition, the feasibility of generating cross-protective immunity against related rickettsial species has also been established, but the molecular basis for these phenomena was not explored. Here, we demonstrate that vaccination of C3H/HeN mice with a recombinant OmpB domain derived from Rickettsia conorii induced high titer humoral immune responses that are capable of recognizing the native OmpB protein at the R. rickettsii outer membrane, but this immunization was not sufficient to induce effective protective immunity. In contrast, animals vaccinated with a corresponding OmpB domain derived from R. rickettsii protected animals from fatal outcomes. These results demonstrate that vaccination with nearly identical antigens may not be an effective strategy to induce wide-ranging protective immunity against related SFG Rickettsia species.

Serological differentiation of murine typhus and epidemic typhus using cross-adsorption and Western blotting

Differentiation of murine typhus due to Rickettsia typhi and epidemic typhus due to Rickettsia prowazekii is critical epidemiologically but difficult serologically. Using serological, epidemiological, and clinical criteria, we selected sera from 264 patients with epidemic typhus and from 44 patients with murine typhus among the 29,188 tested sera in our bank. These sera cross-reacted extensively in indirect fluorescent antibody assays (IFAs) against R. typhi and R. prowazekii, as 42% of the sera from patients with epidemic typhus and 34% of the sera from patients with murine typhus exhibited immunoglobulin M (IgM) and/or IgG titers against the homologous antigen (R. prowazekii and R. typhi, respectively) that were more than one dilution higher than those against the heterologous antigen. Serum cross-adsorption studies and Western blotting were performed on sera from 12 selected patients, 5 with murine typhus, 5 with epidemic typhus, and 2 suffering from typhus of undetermined etiology. Differences in IFA titers against R. typhi and R. prowazekii allowed the identification of the etiological agent in 8 of 12 patients. Western blot studies enabled the identification of the etiological agent in six patients. When the results of IFA and Western blot studies were considered in combination, identification of the etiological agent was possible for 10 of 12 patients. Serum cross-adsorption studies enabled the differentiation of the etiological agent in all patients. Our study indicates that when used together, Western blotting and IFA are useful serological tools to differentiate between R. prowazekii and R. typhi exposures. While a cross-adsorption study is the definitive technique to differentiate between infections with these agents, it was necessary in only 2 of 12 cases (16.7%), and the high costs of such a study limit its use.

Sequence analysis of the 17-kilodalton-antigen gene from Rickettsia rickettsii

DNA obtained from the Sheila Smith strain of Rickettsia rickettsii was digested to completion with the restriction endonucleases BamHI and SalI and ligated with the plasmid vector pUC19. The ligation mixture was used to transform Escherichia coli. A total of 465 bacterial clones were screened for antigen production with hyperimmune rabbit serum. One of the reactive clones, containing a recombinant plasmid designated pSS124, was solubilized and subjected to immunoblot analysis and revealed expression of a 17-kilodalton protein reactive with anti-R. rickettsii serum that comigrated with an antigen from R. rickettsii. A 1.6-kilobase PstI-BamHI fragment from pSS124 was subcloned and continued to direct synthesis of the 17-kilodalton antigen. The nucleotide sequence was determined for this 1.6-kilobase subclone, which encompassed the gene encoding the polypeptide as well as flanking regions containing potential regulatory sequences. The open reading frame consisted of 477 nucleotides that specified a 159-amino-acid protein with a calculated molecular weight of 16,840. The deduced amino acid sequence contained a hydrophobic sequence near the amino terminus that resembled signal peptides described for E. coli. The carboxy terminus was hydrophilic in nature and probably contained the exposed epitopes.

Production and characterization of cloned T-cell hybridomas that are responsive to Rickettsia conorii antigens

T-cell hybridomas produced by the fusion of Rickettsia conorii immune T cells to the AKR thymoma BW 5147 produced interleukin-2 when stimulated with the antigens of three different R. conorii strains. One cloned hybridoma responded only to R. conorii antigens, whereas a second and third cloned hybridoma also responded to the antigens of Rickettsia rickettsii Sheila Smith and Rickettsia sibirica 246, respectively. Antigen responses required antigen-presenting cells, and this interaction was major histocompatibility complex restricted. Fluorescence-activated cell-sorter analysis demonstrated that all three hybridomas were of the Thy-1.2+, Lyt-2- phenotype and that two of the three were L3T4+. These data demonstrated the presence of an antigenic epitope that is R. conorii species specific and other epitopes that are common to various members of the spotted fever group which can stimulate interleukin-2 production by T-cell hybridomas.

Humoral immune response to Rocky Mountain spotted fever in experimentally infected guinea pigs: immunoprecipitation of lactoperoxidase 125I-labeled proteins and detection of soluble antigens of Rickettsia rickettsii

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.

Cross-reactive lymphocyte responses and protective immunity against other spotted fever group rickettsiae in mice immunized with Rickettsia conorii

Lymphocyte proliferation in response to antigens on spotted fever group rickettsiae was used as a method to investigate the group-specific protective immunity to rechallenge characteristic of this group of rickettsiae at the T-cell receptor level. Spleen cells from Rickettsia conorii-immune C3H/HeJ mice proliferated in response to R. rickettsii Sheila Smith, R. sibirica 246, R. australis, and all tested strains of R. conorii (Casablanca, Moroccan, and Malish). Spleen cells from these mice, however, responded poorly or not at all to antigens prepared from the Kaplan or Hartford strain of R. akari. Proliferation of immune T cells maintained as in vitro cell lines showed a similar pattern of reactivity to these antigens; however, response to R. akari was consistently demonstrable. Spleen cells from C3H/HeJ mice immunized with R. akari responded to R. akari and R. conorii antigens as well as antigens from the other spotted fever group rickettsiae. Lymphocytes obtained from lymph nodes draining foot pads infected with R. conorii or R. akari demonstrated cross-reactivity similar to that found with immune spleen cells. If immunization was accomplished with R. conorii antigen emulsified in Freund complete adjuvant, the resulting lymph node cells were able to respond to R. akari antigens. These data suggest that infection with R. conorii induces a population of T lymphocytes that recognize an antigen(s) that also is found on other spotted fever rickettsiae and that may be responsible for cross-protective immunity. This antigen probably is not a major antigen on R. akari.

Immunosuppression associated with the development of chronic infections with Rickettsia tsutsugamushi: adherent suppressor cell activity and macrophage activation

Measures of general immunocompetency such as lymphocyte responses to mitogens and alloantigens and the ability to produce antibody to T-dependent and T-independent antigens were evaluated during the development of chronic infections with Rickettsia tsutsugamushi resulting from subcutaneous infection of BALB/c mice. It was found that a transient immunosuppression was demonstrable regardless of the infecting strain of rickettsiae; however, the immunosuppression produced by the Karp and Kato strains was more pronounced and longer lived. As a marked splenomegaly resulting from inflammatory macrophage influx accompanied this immunosuppression, mitogen- and antigen-induced lymphocyte proliferation was also evaluated after adherent cell depletion or in the presence of indomethacin, and both treatments significantly improved the responses. Isolated splenic macrophages were shown to suppress the responses of lymphocytes from naive mice as well as to exhibit parameters of activation including tumor cell cytolysis and cytostasis and the ability to inhibit the replication of R. tsutsugamushi in vitro. These data suggest an association between macrophage activation involved in rickettsial clearance and a transient immunosuppression.

Incidence of Mediterranean spotted fever in Sardinia in the years 1982-1984

In this work the incidence of Mediterranean spotted fever in the Borough of Cagliari (Sardinia) over the years 1982-1984 is evaluated. Our data show both an overall decrease of the incidence of the disease during this period of time with respect to the year 1980 and a significant reduction in the last year. In addition, the present study confirms the greater reliability of Immunofluorescence respect to the Weil-Felix reaction in revealing Mediterranean spotted fever. Finally we show a marked incidence of significant anti-Rickettsia conori antibodies in apparently healthy individuals, which stresses the not uncommon occurrence of subclinical infection.

Gamma interferon production in response to homologous and heterologous strain antigens in mice chronically infected with Rickettsia tsutsugamushi

The ability of antigen-responsive, thymus-derived lymphocytes to produce immune (gamma) interferon was investigated during the development and expression of cellular immunity to Rickettsia tsutsugamushi. C3H/HeDub mice infected subcutaneously with the Gilliam strain developed the ability to produce serum interferon in response to intravenously inoculated antigen which correlated with the development of resistance to intraperitoneal rechallenge. Antigen-responsive lymphocytes, measured by interferon production and proliferation, were first apparent in draining lymph node cells, but spleen cell responses were detectable relatively soon after the appearance of reactive lymph node cells. The peak spleen cell response was of a greater magnitude and was found to be relatively long-lived. Reactivity to heterologous strains of R. tsutsugamushi also developed after immunization and paralleled the homologous responses, although reactivity was greatest to homologous antigens. Responses to heterologous strains differed in magnitude and time of appearances; however, immune mice resisted challenge with all strains of R. tsutsugamushi tested.

Production of gamma interferon in mice immune to Rickettsia tsutsugamushi

C3H/He mice immunized by subcutaneous infection with Rickettsia tsutsugamushi Gilliam were examined for the production of immune interferon after intravenous administration of irradiated strain Gilliam antigen, in supernatants of immune lymphocytes stimulated with specific antigen, and after a secondary challenge with viable rickettsiae. Mice administered various doses of irradiated whole-organism antigen 28 days after immunization showed circulating levels of interferon which peaked 4 h after inoculation and were antigen dose dependent. The interferon produced was pH 2 sensitive and stable at 56 degrees C for 1 h and was neutralized by antiserum directed against immune, but not against alpha/beta, interferon. The production of another lymphokine, macrophage migration inhibition factor, paralleled that of interferon. The interferon produced by cultures of spleen cells obtained from immune animals was antigen specific and dose dependent. Peak levels were obtained 48 to 72 h after the addition of antigen. The interferon produced by spleen cell cultures after stimulation with Gilliam antigen was characterized as immune interferon by the same physical and antigenic criteria used for serum interferon. Interferon was produced in vitro by the Thy-1.2+ lymphocyte and required the presence of a spleen-adherent cell population. Immune mice produced high circulating levels of immune interferon after intraperitoneal challenge with viable rickettsiae, which suggested a possible role for interferon in the resistance of immune mice to rechallenge with R. tsutsugamushi.

Role of T-lymphocytes in production of antibody to antigens of Rickettsia tsutsugamushi and other Rickettsia species

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 a great or greater than in the thymus-bearing mice and demonstrated similar kinetics. In contrast, athymic BALB/c mice infected either intraperitoneally or subcutaneously with the Gilliam strain of R. tsutsugamushi failed to produce demonstrable antibody. The requirement of thymus-dependent lymphocytes for antibody production to R. tsutsugamushi was further suggested by the demonstration of antibody production after transfer of immune thymus-dependent lymphocytes to athymic mice and the demonstration of R. tsutsugamushi-specific T helper cells in immune thymus-bearing mice. The antibody produced in athymic mice after infection with R. akari, R. conorii, and R. typhi was predominantly immunoglobulin M, based on isotype-specific radioimmunoassays and sucrose gradient fractionation. Furthermore, the antibody produced by athymic mice in response to R. akari infection reacted with a carbohydrate-containing outer membrane component.

Development of specific and cross-reactive lymphocyte proliferative responses during chronic immunizing infections with Rickettsia tsutsugamushi

The development of antigen-responsive lymphocytes was followed in mice immunized with the Gilliam, Karp, or Kato strains of Rickettsia tsutsugamushi by utilizing an in vitro lymphocyte proliferation assay. Subcutaneous immunization with viable rickettsiae of all three strains resulted in the appearance of lymphocytes in the spleen responding to irradiated tissue culture-grown rickettsiae used as stimulating antigens. Although all animals demonstrated antigen-induced proliferation elicited by homologous antigen by 14 days after immunization, the time of peak responsiveness varied, depending on the strain of rickettsiae used for immunization. In all cases, peak proliferative responses occurred at a time after immunization that was after the previously reported time after immunization at which resistance to rechallenge was observed. Reactivity to heterologous strains of R tsutsugamushi developed roughly in parallel with homologous reactivity in Karp- and Gilliam-immunized mice, with a marked degree of heterologous reactivity evident. Kato-immunized mice demonstrated greater reactivity to heterologous antigens early in the development of antigen reactivity and demonstrated a somewhat greater degree of cross-reactivity, relative to homologous responses, than the other groups. It was found that nylon wool-nonadherent immune cells, if cultured with antigen and adherent cells obtained from normal spleens or peritoneal exudates, responded in culture. The thymus-derived lymphocyte nature of the responding cell was further suggested when treatment of immune spleen cells with anti-Thy 1.2 serum and complement eliminated antigen response.

Gamma-irradiated scrub typhus immunogens: development of cell-mediated immunity after vaccination of inbred mice

Mice immunized with three injections of gamma-irradiated Karp strain of Rickettsia tsutsugamushi were evaluated for the presence of cell-mediated immunity by using delayed-type hypersensitivity, antigen-induced lymphocyte proliferation, and antigen-induced lymphokine production. These animals also were evaluated for levels of circulating antibody after immunization as well as for the presence of rickettsemia after intraperitoneal challenge with viable Karp rickettsiae. After immunization with irradiated Karp rickettsiae, a demonstrable cell-mediated immunity was present as evidenced by delayed-type hypersensitivity responsiveness, lymphocyte proliferation, and production of migration inhibition factor and interferon by immune spleen lymphocytes. Also, a reduction in circulating rickettsiae was seen in mice immunized with irradiated rickettsiae after challenge with 1,000 50% mouse lethal doses of viable, homologous rickettsiae. All responses except antibody titer and reduction of rickettsemia were similar to the responses noted in mice immunized with viable organisms. Antibody levels were lower in mice immunized with irradiated rickettsiae than in mice immunized with viable rickettsiae. Furthermore, mice that were immunized with viable rickettsiae demonstrated markedly lower levels of rickettsemia after intraperitoneal challenge compared with either mice immunized with irradiated rickettsiae or nonimmunized mice.

Host defenses in experimental scrub typhus: delayed-type hypersensitivity responses of inbred mice

Delayed-type hypersensitivity responses of inbred mice during the course of lethal and chronic infections with strains of Rickettsia tsutsugamushi were evaluated by using the influx of radiolabeled cells into antigen-injected ears. Congenic strains of C3H mice, which previously have been shown to be resistant (C3H/RV) or sensitive (C3H/HeDub) to lethal intraperitoneal infection with the Gilliam strain of rickettsiae, both expressed delayed-type hypersensitivity early in the course of infection (5 to 7 days). The sensitive C3H/HeDub mice, however, exhibited a marked decline in reactivity just before death. In contrast, reactivity of C3H/RV mice remained high through day 9 and declined slowly through day 15 after infection. Similar results were obtained when BALB/c mice were infected with either the Karp or the Gilliam strain of rickettsiae, which produce a lethal or nonlethal infection, respectively, in this strain of mice. Rechallenge of C3H/RV mice elicited a rapid increase in reactivity, suggesting a secondary memory response. To analyze delayed-type hypersensitivity during chronic infection, C3H/HeDub mice were immunized by subcutaneous infection with the Gilliam strain of R. tsutsugamushi, and both delayed-type hypersensitivity reactivity and resistance to intraperitoneal challenge were examined. Delayed-type hypersensitivity reactivity developed slowly and peaked at 21 days postimmunization, which correlated with resistance to intraperitoneal challenge. Delayed-type hypersensitivity reactivity declined thereafter, but resistance to intraperitoneal challenge remained through 28 days postimmunization. Delayed-type hypersensitivity reactivity increased after secondary challenge at 28 days, again suggesting antigen memory generated by primary immunization. Transfer of delayed-type hypersensitivity reactivity was accomplished by using immune thymus-derived splenic lymphocytes isolated with nylon-wool columns. Abrogation of the ability of immune spleen cells to transfer delayed-type hypersensitivity reactivity after treatment with anti-Thy 1.2 alloantiserum and complement further supported the view that delayed-type hypersensitivity responses to scrub typhus rickettsiae were mediated by thymus-derived lymphocytes.

Isolation of species-specific protein antigens of Rickettsia typhi and Rickettsia prowazekii for immunodiagnosis and immunoprophylaxis

A simple procedure for the selective isolation of the protective species-specific protein antigens (SPAs) of Rickettsia typhi and Rickettsia prowazekii was developed to permit use of the SPAs in the immunodiagnosis and immunoprophylaxis of typhus infections. Although the SPAs were readily extracted from lysozyme- or detergent-treated rickettsiae, as measured by rocket immunoelectrophoresis, other polypeptides were also present, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In contrast, both water and seven buffers, each at a 10 mM concentration and pH 7.6, were nearly equally effective in the selective release of the SPAs from whole cells by extraction for 30 min at 45 degrees C. High-ionic-strength buffers and MgCl2 abolished this SPA release, thus suggesting that divalent cations were important in the binding of the SPAs to the cell envelope. The efficacy of the dilute buffer extraction procedure for isolation of large amounts of SPAs was tested by further characterization of the supernatants obtained by centrifugation (200,000 x g) of two successive tris-(hydroxymethyl)aminomethane-hydrochloride buffer (Tris) extracts. With this procedure, between 10 and 15 mg of SPA was obtained from 100 mg of purified rickettsiae. Although low-molecular-weight ribonucleic acid fragments were released into the Tris extracts in significant amounts, only the SPAs were detected, in significant quantities, as measured by polyacrylamide gel electrophoresis and rocket immunoelectrophoresis. The Tris extracts contained the same major and minor SPA polypeptides as those observed previously in SPA preparations obtained by extensive diethylaminoethyl-cellulose column chromatography, but the Tris SPAs were more satisfactory antigens in an enzyme-linked immunosorbent assay.

Antigens of scrub typhus rickettsiae: separation by polyacrylamide gel electrophoresis and identification by enzyme-linked immunosorbent assay

Antigens of plaque-purified Rickettsia tsutsugamushi strains Gilliam, Karp, and Kato were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and were analyzed by an enzyme-linked immunosorbent assay. Six antigens were identified in each of the three prototype strains; in strain Gilliam, these antigens were located in the cell envelope fraction of the organisms. Reactivity of these isolated antigens with homologous or heterologous immune sera indicated that different macromolecules existed in all three strains, although they exhibited very similar mobilities during electrophoresis. Antigens of strain Gilliam reacted equally well with antibodies directed against Gilliam, Karp, or Kato rickettsiae. However, strains Karp and Kato each had two distinct antigens which did not react with heterologous antisera. R. tsutsugamushi antigens retained immunogenicity after electrophoresis, and antisera raised against them reacted with intact organisms and exhibited specificity in reactions with isolated antigens.

Partial purification and characterization of the major species-specific protein antigens of Rickettsia typhi and Rickettsia prowazekii identified by rocket immunoelectrophoresis

Species-specific antigens from Rickettsia typhi and Rickettsia prowazekii were readily solubilized by French pressure cell extraction or sonication of Renografin density gradient-purified rickettsiae and were identified by rocket immunoelectrophoresis. As measured by quantitative rocket immunoelectrophoresis, the species-specific typhus rocket antigens (STRAs) appeared to be proteins; they were denatured by heating at 56 degrees C for 30 min but not by 50 degrees C treatment, and they were sensitive to pronase and trypsin but were not affected by periodate oxidation, glycosidases of various specificities, phospholipase A, or lipase. STRAs from both R. typhi and R. prowazekii were separated from common antigens by DE52 column chromatography of 100,000-X-g supernatant fractions of rickettsial extracts. The purified STRAs were characterized by crossed immunoelectrophoresis, by polyacrylamide gel electrophoresis on Davis and sodium dodecyl sulfate gels, and by an enzyme-linked immunosorbent assay. The two purified STRAs were proteins with similar native electrophoretic mobilities in agarose and polyacrylamide gels, and these proteins had similar polypeptide patterns on sodium dodecyl sulfate gels. Most of the STRA activity migrated as a single protein band on sodium dodecyl sulfate-polyacrylamide and Davis polyacrylamide gels, although minor protein bands with STRA activity were also detected. The major STRA proteins constituted 10 to 15% of the total cellular protein of R. typhi and R. prowazekii. According to sensitive enzyme-linked immunosorbent assay titrations, the STRA of R. prowazekii had substantial cross-reactivity with rabbit antiserum prepared against R. typhi, as shown also by rocket immunoelectrophoresis, whereas the STRA of R. typhi reacted only very weakly with antiserum prepared against R. prowazekii according to the enzyme-linked immunosorbent assay and not at all according to rocket immunoelectrophoresis.

Radioiodination of an outer membrane protein in intact Rickettsia prowazekii

Intact Rickettsia prowazekii was radiolabeled with the glucose oxidase-lactoperoxidase method of iodination. Separation of the rickettsial extract into cytoplasmic, outer and inner membrane fractions demonstrated that the outer membrane was preferentially labeled. Analysis of the polypeptides of these fractions on high-resolution slab polyacrylamide gels showed that most of the 125I was in polypeptide T49, an outer membrane constituent. Additional outer membrane polypeptides were iodinated in broken envelope preparations, demonstrating that T49 is uniquely accessible to the external environment and the asymmetric polypeptide organization of the outer membrane.

Properties of selected rickettsiae of the spotted fever group

Eight strains of spotted fever group rickettsiae were studied to gain insight into the extent of variation of their properties. Two standard strains of Rickettsia rickettsii and one strain of Rickettsia conorii were included among the eight for comparison. The molar percentage of guanine plus cytosine for each strain did not differ significantly from that for R. rickettsii, 32.6 +/- 0.7%. Two strains caused extended fever in guinea pigs, one strain caused fever of short duration, and the other strains induced little or no fever. Polyacrylamide gel electrophoresis of the detergent-solubilized rickettsial proteins indicated that the protein content of all strains, except the two strains of R. rickettsii, were different, particularly in the molecular weight range of 40,000 to 60,000. Virulent strains produced large clear plaques in Vero cells monolayers; the strains of low virulence generally produced smaller or more turbid, or both, plaques. On the basis of agglutination reactions with rabbit antisera, the eight strains were placed into five serotypes. These results indicate considerable heterogeneity in properties of spotted fever group rickettsiae in the United States.

Separation of inner and outer membranes of Rickettsia prowazeki and characterization of their polypeptide compositions

Rickettsia prowazeki were disrupted in a French pressure cell and fractionated into soluble (cytoplasm) and envelope fractions. The envelope contained 25% of the cell protein, with the cytoplasm containing 75%. Upon density gradient centrifugation, the envelope fraction separated into a heavy band (1.23 g/cm3) and a lighter band (1.19 g/cm3). The heavy band had a high content of 2-keto-3-deoxyoctulosonic acid, a marker for bacterial lipopolysaccharide, but had no succinic dehydrogenase, a marker for cytoplasmic membrane activity, and therefore represented outer membrane. The lighter band exhibited a high succinate dehydrogenase activity, and thus contained inner (cytoplasmic) membrane. Outer membrane purified by this method was less than 5% contaiminated by cytoplasmic membrane; however, inner membrane from the gradient was as much as 30% contaminated by outer membrane. The protein composition of each cellular fraction was characterized by sodium dodecyl sulfate--polyacrylamide gel electrophoresis. The outer membrane contained four major proteins, which were also major proteins of the whole cell. The cytoplasmic membrane and soluble cytoplasm exhibited a more complex pattern on gels.

Phospholipid composition of Rickettsia prowazeki grown in chicken embryo yolk sacs

The phospholipid composition and phospholipid fatty acid composition of purified Rickettsia prowazeki were determined. The lipid phosphorous content was 6.8 +/- 1.3 microgram/mg of total rickettsial protein. The major phospholipid was phosphatidylethanolamine (60 to 70%); phosphatidylglycerol constituted 20%, and phosphatidylcholine constituted 15%. Small amounts of phosphatidylserine and cardiolipin were detected. The principal fatty acids were 18:1, 16:1, and 16:0. The fatty acid composition of the phosphatidylcholine in the rickettsial extracts was very different than that of the other rickettsial phosphatides and very similar to that of normal yolk sac phosphatidylcholine. The specific of the phosphatidylcholine of rickettsiae grown in the presence of 32P was markedly lower than that of phosphatidylethanolamine and phosphatidylglycerol. It is suggested that the phosphatidylcholine in the rickettsial extract is yolk sac derived and either tightly absorbed or exchanged into the rickettsial membrane.

Surface proteins of typhus and spotted fever group rickettsiae

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 micronM 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 micronM 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.

Rickettsial indirect hemagglutination test: isolation of erythrocyte-sensitizing substance

The erythrocyte-sensitizing substances (ESS) of Rickettsia prowazekii and R. conorii were characterized by biological and chemical criteria. ESS could be derived from either soluble or particulate complement-fixing antigens obtained by ether extraction of rickettsiae. The soluble complement-fixing antigen exhibited two peaks of serological activity in potassium tartrate density gradients. The particulate complement-fixing antigen coincided with the more dense peak but was distinguishable by its sedimentation in rate-zonal sucrose gradients. ESS was obtained from each of the complement-fixing-reactive gradient peaks by extraction with hot alkali and was quantified by a modified indirect hemagglutination test. These ESS preparations sedimented similarly in potassium tartrate gradients and were shown to contain protein and carbohydrate, both by colorimetric tests and by incorporation of radioactive precursors. The serological activity of ESS was unaffected by trypsin, but both antigenicity and erythrocyte-binding capacity were reduced after exposure to sodium metaperiodate. Highly purified ESS was rapidly inactivated by potassium tartrate and required stabilization with bovine plasma albumin.

Biochemical characteristics of typhus group rickettsiae with special attention to the Rickettsia prowazekii strains isolated from flying squirrels

Six strains of Rickettsia prowazekii, two derived from human infections and four isolated from flying squirrels, two strains of R. typhi, and the single available strain of R. canada, were characterized by several biochemical procedures. The electrophoretic patterns on polyacrylamide gels of rickettsial proteins solubilized by sodium dodecyl sulfate revealed several species differences, but strains of the same species appeared to have identical patterns. Cytoplasmic fractions of the rickettsiae were examined for enzymatic activities and for polyacrylamide gel isoelectric focusing patterns. Some species differences were encountered in the activities or ratios of activities of glutamate-oxaloacetate transaminase, glutamate dehydrogenase, and malate dehydrogenase. When polyacrylamide gels were stained for malate dehydrogenase after electrophoresis, a single band became apparent with single extracts or mixtures of two strains of R. prowazekii, but two bands were seen with mixtures of a strain of R. prowazekii and one of R. typhi. The isoelectric focusing patterns of the soluble proteins revealed numerous species differences, especially between R. canada and the other two species, and a few differences among the strains of R. prowazekii. The patterns of the two human strains, Breinl and E(R), differed in at least one location, and both differed from the flying squirrel strains in the displacement of one band. One of the flying squirrel strains, GvF-16, contained a protein band not seen in the other five strains. Despite these minor differences, a striking similarity was revealed by all the biochemical tests performed between the R. prowazekii strains of human and flying squirrel origin.

Host defenses in experimental scrub typhus: genetics of natural resistance to infection

Genetic resistance to lethal infection with Rickettsia tsutsugamushi was studied in over 30 inbred strains, inbred hybrids, and outbred stocks of mice. Inbred mice infected intraperitoneally with the Gilliam strain of R. tsutsugamushi showed three patterns of response: susceptible (A/HeJ, C3H/HeDub, C3H/HeJ, C3H/HeN, C3H/St, CBA/J, DBA/1J, DBA/2J, and SJL/J), resistant (AKR/J, BALB/cDub, BALB/cJ, C57BL/6J, C57L/J, and SWR/J), and selectively resistant (A/J). The selectively resistant pattern was characterized by random deaths occurring throughout the titration range and was also observed in three of the six outbred mouse stocks surveyed. No correlation was evident between the H-2 haplotype of inbred mice and their response to Gilliam infection. The progeny from five different Gilliam-resistant by Gilliam-susceptible inbred parental crosses were all resistant. Study of F(1), F(2), and parental backcross generations of BALB/cDub (resistant) and C3H/HeDub (susceptible) hybrids indicated resistance was dominant and was controlled by a single gene or a closely linked cluster of genes that were autosomal and not linked to coat color. The resistance of BALB/cDub mice was not due to an inability of host cells to support rickettsial growth, since C3H/HeDub and BALB/cDub embryo cell cultures supported similar growth of Gilliam organisms. C3H/HeDub mice, although susceptible to intraperitoneal Gilliam infection, were capable of mounting an immune response to Gilliam antigens, since subcutaneous infection was not lethal and did protect animals against subsequent intraperitoneal challenge with either the Gilliam or Karp strains of R. tsutsugamushi.