Isolation and partial characterization of an immunogenic moiety obtained from Salmonella typhimurium

A broadly applicable approach to T cell epitope identification: application to improving tumor associated epitopes and identifying epitopes in complex pathogens

Epitopes are a hallmark of the antigen specific immune response. The identification and characterization of epitopes is essential for modern immunologic studies, from investigating cellular responses against tumors to understanding host/pathogen interactions especially in the case of bacteria with intracellular residence. Here, we have utilized a novel approach to identify T cell epitopes exploiting the exquisite ability of particulate antigens, in the form of beads, to deliver exogenous antigen to both MHC class I and class II pathways for presentation to T cell hybridomas. In the current study, we coupled this functional assay with two distinct protein expression libraries to develop a methodology for the characterization of T cell epitopes. One set of expression libraries containing single amino acid substitutions in a defined epitope sequence was interrogated to identify epitopes with enhanced T cell stimulation for a MHC class I epitope. The second expression library is comprised of the majority of open reading frames from the intracellular pathogen and potential biowarfare agent, Francisella tularensis. By automating aspects of this technology, we have been able to functionally screen and identify novel T cell epitopes within F. tularensis. We have also expanded upon these studies to generate a novel expression vector that enables immunization of recombinant protein into mice, which has been utilized to facilitate T cell epitope discovery for proteins that are critically linked to Francisella pathogenicity. This methodology should be applicable to a variety of systems and other pathogens.

Immunogenic mycobacterial ribosomal and ribonucleic Acid preparations: chemical and physical characteristics

Five to 20% linear sucrose gradients were used to obtain sedimentation patterns of mycobacterial ribosomes, ribosomal subfractions, and ribonucleic acid (RNA) preparations. Classical 70S ribosomes were obtained when 10(-1)m magnesium chloride was used. These, when dialyzed against 10(-4)m MgCl(2), yielded typical 50S, 30S, and smaller ribosomal subunits. The 30S subunits were the most immunogenic under these conditions. A ribosomal preparation containing subunits which varied from 2.5 to 40S was fractionated by collecting five fractions from a sucrose gradient; based upon the amount of nucleic acid present, the fraction containing the 40S particles was most immunogenic. Physical and chemical evidence suggested that mycobacterial RNA preparations extracted with 65% ethyl alcohol from the ribosomes and diluted in distilled water, were either double-stranded, or mostly double-helical, or had a highly organized secondary structure. This was based on the following observations. (i) Native RNA was resistant to trace amounts of ribonuclease. (ii) The approximate T(m) value in SSC buffer (0.15 m NaCl plus 0.015 m sodium citrate) was greater than 85 C and in 0.1 SSC buffer was 55 C; the RNA diluted in SSC buffer produced a hypochromic effect on cooling at room temperature. (iii) Formaldehyde, in the presence of SSC buffer, decreased the T(m) of the RNA to approximately 55 C, and there was no hypochromic effect on cooling. (iv) Formaldehyde did not increase the wavelength of maximal adsorption of the RNA. (v) The purine/pyrimidine ratio was close to one. (vi) The major peak of the RNA sedimented in the more dense zones of the sucrose gradients. There was a relationship between the sedimentation pattern obtained with the RNA-protein subunits on sucrose gradients and immunogenicity; several examples are given. RNA-protein complexes of approximately 14 to 20S, and occasionally 23S in the major peak, appeared to produce the highest immune response. Smaller RNA-protein complexes such as 6S, which were obtained when the RNA preparation was diluted in certain buffers, were much less immunogenic. This was confirmed by collecting five fractions from sucrose gradients and finding the third fraction (containing RNA-protein complexes approximately 15 to 16S) the most immunogenic. Immunogenic activity was apparently related to the structure of the RNA since it was maximal when the RNA appeared to be either double stranded, double helical, or had a highly organized structure.

Immunogenicity of Ribonucleic Acid Preparations Obtained from Salmonella typhimurium

Mice immunized with purified whole-cell ribonucleic acid (RNA), RNA from the bacterial "particulate" fraction, and ribosome-associated RNA obtained from Salmonella typhimurium were found to be resistant to subsequent challenge infection with virulent salmonellae. Chemically, the immunogenic nucleic acid fractions contained from 1 to 3% "contaminant" material defined (based on the mean of 19 different preparations) as protein (0.24%), deoxyribonucleic acid (0.43%), methyl pentose (0.64%), hexose (1.58%), and undefined carbohydrate (0.76%). Heptoses and lipoidal material were not detectable in any of the immunogenic preparations examined. Physically, the nucleic acid preparations, after analytical ultracentrifugation, exhibited three boundaries similar to those reported elsewhere in comparable systems: 4 to 5S, 16S, and 23S. An evaluation of the immunity induced by the ribosome-associated RNA established that the immune response was (i) comparable to that induced 15 days postimmunization with live salmonellae and by ribosomal vaccines, but greater at 30 days postimmunization than that in mice immunized with attenuated salmonellae; (ii) dependent on the quantity of immunogen administered; (iii) dependent on the size of the infective inocula; (iv) inhibited at 15 but not at 30 days postimmunization when the immunogenic nucleic acid preparations were incorporated into Freund's incomplete adjuvant, (v) reduced or lost by dialysis in relatively high or low immunizing doses, respectively; and (vi) unaffected by enzymatic treatment of the preparations with trypsin, deoxyribonuclease, Pronase plus pancreatic ribonuclease, or pancreatic ribonuclease alone. The possible mode of action of ribosome-associated RNA in inducing an immune response to subsequent challenge infection with the homologous organism is discussed.

Protection against pneumococcal infection by a ribosomal preparation

A subcellular extract prepared from nonencapsulated Diplococcus pneumoniae type 3 protected mice against a subsequent challenge with virulent D. pneumoniae types 1, 2, 3, and 7. Potency ratios ranged from 25 (type 3) to >1,175 (type 1). The immunity induced in mice by this preparation was best obtained by intraperitoneal inoculation followed by intravenous challenge. Mice immunized in this manner were protected up to 12 weeks and could withstand a challenge of several hundred LD(50). The protection was destroyed by treatment of the preparation with ribonuclease and was decreased by treatment with protease. The preparation consisted of 60.5% ribonucleic acid, 29.1% protein, 6.3% deoxyribonucleic acid, and 4.0% hexose. Ultracentrifugation studies indicated that this extract had five constituents which are compatible with ribosomal material.

Immunogenicity and protective efficacy offered by a ribosomal-based vaccine from Shigella flexneri 2a

Shigellosis is a major form of bacillary dysentery caused by Shigella infection. Shigella ribosome-based vaccines (SRV), considered among the potent vaccine candidates, are composed of O-antigen and ribosome isolated from S. flexneri 2a. To investigate the immunogenicity and protective efficacy of SRV, mice were vaccinated with SRV via the intranasal (i.n.) route. Interestingly, robust levels of Shigella-derived LPS-specific IgG and IgA Abs and antibody-forming cells were elicited in systemic and mucosal compartments following two i.n. administrations of SRV. Groups of mice receiving i.n. SRV developed milder pulmonary pneumonia upon challenge with virulent S. flexneri 2a than did those receiving parenteral SRV. We further found that the MyD88-dependent TLR2 signal partially mediates SRV-induced mucosal immunity, with the exception of TLR4- and TLR5-governed innate immunity. Most importantly, polymeric immunoglobulin receptor knockout (pIgR-/-) mice, which lack secretory IgA Ab, were afforded less protective efficacy than were wild-type mice. It can be concluded then that SRV is immunogenic and provides protective efficacy in mice. It can also be surmised that a mucosal SRV vaccine would be particularly relevant in targeting shigellosis, which provokes inflammation in the human colon.

Development of a mucosal complex vaccine against oral Salmonella infection in mice

We examined the immunogenicity of a Salmonella enterica complex vaccine (CV), consisting of flagellin and polysome purified from serotype Typhimurium LT2. CV plus cholera toxin (CT), in three oral doses given at 7-day intervals, conferred complete protection on C57BL/6 mice against lethal oral infection with a wild-type strain. It elicited mucosal IgA > IgG2a > IgG1 and systemic IgG2a > IgG1 > IgA antibodies to flagellin and polysome, and delayed footpad response (DFR) to both antigens. In Peyer's patches (PPs) and lamina propria (LP), IgA was produced under a Th1-dominant environment; CD4+T cells from produced interleukin (IL)-2, interferon (IFN)-gamma, and IL-10 by stimulation with salmonella extract. On the same protocol, flagellin plus CT induced flagellin-specific mucosal and systemic IgA and IgG1 antibodies, CD4+T cells producing IL-10 and IFN-gamma in PPs and LP, and only minimal levels of flagellin-specific DFR. Polysome plus CT induced polysome-specific mucosal and systemic IgG2a in addition to IgG1 and IgA antibodies, CD4+T cells producing IFN-gamma and IL-2 in PPs and LP, and polysome-specific DFR. These two vaccines, however, conferred at most 50-60% survival rates. Our results suggest that polysomes in CV provide effective adjuvant activity for the induction of both mucosal and systemic Th1-biased responses toward flagellin.

Delayed-type hypersensitivity activity of the Brucella L7/L12 ribosomal protein depends on posttranslational modification

The ribosomal protein L7/L12 isolated from Brucella melitensis induces a delayed-type hypersensitivity (DTH) reaction in brucella-sensitized guinea pigs. Surprisingly, the recombinant brucella L7/L12 protein expressed in Escherichia coli as a fusion protein with a six-histidine tag cannot elicit such a reaction. The six histidines tagged to the recombinant L7/L12 protein were removed enzymatically, but the resulting protein did not induce a DTH reaction in sensitized animals. Incubation of the recombinant L7/L12 fusion protein in a B. melitensis lysate endowed the recombinant protein with a DTH activity, suggesting that the recombinant protein was modified by this treatment. Glycosylation or phosphorylation of the recombinant L7/L12 protein could not be detected. On the other hand, radiolabeled palmitic acid was found to be incorporated to the recombinant protein during its incubation in the brucella lysate. This incorporation was specific for the brucella L7/L12 protein and was inhibited when the brucella lysate was frozen and thawed before the incubation. The data reported here indicate that posttranslational modification of L7/L12 protein comprising at least an acylation step is required for the brucella L7/L12 DTH activity.

Brucella ribosomal protein L7/L12 is a major component in the antigenicity of brucellin INRA for delayed-type hypersensitivity in brucella-sensitized guinea pigs

A delayed-type hypersensitivity (DTH) reaction in the course of brucellosis in humans and animals can be revealed by the brucellin INRA (Brucellergen) skin test. Brucellergen is composed of more than 20 proteins of different molecular weights. A 12-kDa protein eliciting DTH in Brucella melitensis Rev1-sensitized guinea pigs was found to be a significant component for the allergenic properties of Brucellergen. Sequencing of the gene encoding this protein identified it as the L7/L12 ribosomal protein. The L7/L12 gene of B. melitensis was amplified by PCR and subcloned in the Escherichia coli pQE30 plasmid. The resulting recombinant protein did not produce a DTH reaction in sensitized animals. It was used to raise specific antibodies in a rabbit. Affinity chromatography with these antibodies was used to isolate a single protein from Brucellergen and from B. melitensis cytosol preparations which produced a DTH reaction in guinea pigs sensitized with B. melitensis Rev1. N-terminal amino acid sequencing of the protein confirmed that it was the L7/L12 ribosomal protein. This is the first complete report on the involvement of a defined bacterial ribosomal protein in the DTH response of animals infected with intracellularly multiplying bacteria.

Requirement of the conformational stability of a Salmonella ribosomal vaccine for its mouse protection

The 43-kDa non-O antigenic component isolated from the crude ribosomal fraction of Salmonella typhimurium [9] was further purified by affinity chromatography (43-kDa protein: 43-kDp). Immunization with 43-kDp did not induce complete mouse protection in CF1 mice to 500 LD50 of S. typhimurium, although it elicited a substantial IgG antibody response. The 43-kDp exhibited the mitogenicity to splenocytes (CF1 and C3H/HeJ) and B cell-rich populations (CF1). Complexing 43-kDp with the compact ribosomes of Streptococcus pyogenes by formaldehyde (complex vaccine: CV) elicited both IgM and IgG antibodies to 43-kDp. CV induced a boosting effect to enhance IgG antibody response. Moreover, CV generated delayed-type hypersensitivity to salmonella antigens and also conferred complete protection against 500 LD50 challenge of S. typhimurium to CF1 mice. These abilities of CV were reduced or impaired by RNase digestion. CV was able to induce partial or complete protection in inbred mouse strains (C3H/HeN, C3H/HeJ, DBA/2 and A/J). These data, in addition to other reports, suggest that conformational stability between ribosomes and contaminating substances such as 43-kDp or O-antigens might be required for the overall effects of the ribosomal vaccine.

Polysaccharide nature of O antigen in protective ribosomal preparations from Shigella: experimental evidence and implications for the ribosomal vaccine concept

Shigella ribosomal vaccine (SRV) was previously shown to be highly active in induction of mucosal and systemic O-antibody response and protection against Shigella infection in guinea pigs and monkeys. In this study, the O-specific component (OSC) was isolated from the SRV by affinity chromatography using rabbit O antibodies coupled to CNBr-Sepharose. The results of the reaction with carbocyanine dye as well as chemical data show that ribosomal OSC is devoid of lipid A and KDO, which are characteristic of classical LPS. The comparison of OSC with various LPS-related substances led to the conclusion that ribosomal OSC is similar to and probably identical with cytoplasmic O polysaccharide (L hapten), an O-side-chain polymer which accumulates in cytoplasm. It is hypothesized that the extremely high immunogenicity of SRV depends on a cooperative action of OSC, representing an epitope-specific part of the vaccine, and a ribosomal particle which serves as a vector, providing amplification of the immunogenic effect. The data obtained indicate the presence of a non-covalent link between the two components of the ribosomal vaccine.

Analysis of cell wall and membrane contamination of ribosomal preparations from Streptococcus mutans

A ribosomal preparation from a cariogenic strain of Streptococcus mutans was examined for cell wall and membrane contamination. A biochemical characterization established that the preparation contained 61.0% RNA and 39.0% protein. Carbohydrate was not detected by phenol-sulfuric acid or methyl pentose assays. Glucosyltransferase and D-succinate dehydrogenase, which are cell wall- and membrane-associated enzymes, respectively, were not found. However, D-lactate dehydrogenase, another membrane-associated enzyme, was present in the preparation. A comparison of two-dimensional gel electropherograms of a mixture of cell walls and membranes and the S. mutans ribosomal preparation revealed contamination of the latter sample with at least six cell wall- or membrane-associated proteins. Adsorption of a rabbit antiserum raised against the ribosomal preparation with whole S. mutans cells abrogated antibodies directed against at least two proteins from the ribosomal preparation. Immunodiffusion plates showed reactivity of this antiserum against preparations of purified lipoteichoic acid from Streptococcus pyogenes and S. mutans. Adsorption of rat and rabbit antisera against the ribosomal preparation with the cell wall-derived materials glucosyltransferase, lipoteichoic acid, glucan, and a Rantz-Randall extract reduced the concentration of antibodies against the ribosomes by as much as 10-fold. These data indicated that the preparation was contaminated with at least six cell wall proteins, one cell membrane-associated enzyme, and lipoteichoic acid.

Immunoprotective activity of capsular polysaccharide in Klebsiella pneumoniae ribosomal preparations does not involve ribonucleic acid

Two peaks were obtained by cesium chloride density gradient ultracentrifugation of Klebsiella pneumoniae ribosomal preparations. Peak I contained capsular polysaccharide, lipopolysaccharide, protein, and less than 0.5% ribonucleic acid. Peak II consisted mainly of ribonucleic acid, with low amounts of protein and capsular polysaccharide. Expressed as capsular polysaccharide content, the 50% protective dose of peak I and of nonfractionated ribosomal preparations was nearly constant (2.6 and 1.2 ng, respectively). Since peak I contained less than 0.5% ribonucleic acid, these results provide evidence that ribosomal ribonucleic acid is not required for protection of mice by K. pneumoniae capsular polysaccharide which contaminates ribosomal preparations.

Antigenic modification: its relation to protective host resistance in murine salmonellosis

Both the physical state of the immunogen and the route of immunization were found to be extremely important in inducing effective host resistance against salmonellosis.

On the immunogenicity of ribosomes and ribosomal proteins isolated from Klebsiella pneumoniae and Streptococcus pneumoniae

The two pathogenic species Streptococcus pneumoniae and Klebsiella pneumoniae were used to analyze the immunogenic role of proteins in ribosomal preparations. The protective activity of ribosomes prepared from either strain and further purified by washing with high-salt concentrations, followed or not by sucrose gradient separation of the particles, was identical to that of crude unwashed ribosomes. Similarly, no substantial alteration of the level of protection was observed after treatment with the antibiotic puromycin. Therefore, the immunizing efficacy of ribosomes does not appear to be due either to the nonribosomal proteins adsorbed at the surface of organelles or to the growing polypeptide chain. It seems rather to be attributable to the structural ribosomal proteins themselves, which were indeed shown to induce alone a significant level of protection.

Intranasal immunization of mice against Pasteurella multocida

A potassium thiocyanate (KSCN) extract of Pasteurella multocida serotype III:A was shown to protect mice from an intranasal challenge with up to 300 50% lethal doses of P. multocida. In addition to preventing death, bacteria were rapidly cleared from the lungs of immunized mice so that by 72 to 96 h postchallenge no bacteria were present in the lungs of immunized mice, whereas up to 10(9) bacteria were present in lungs of nonimmunized mice. Immunization by the intranasal route was slightly better than that by the intramuscular route. Protection was considered specific, since immunization with P. multocida protected only against P. multocida and not against Salmonella agona. Furthermore, a similar KSCN extract from P. haemolytica did not protect against P. multocida challenge. A comparison of the KSCN extract with a Formalin-killed bacterin suggested that the KSCN extract may be superior to the bacterin.

Immunogenicity of ribosomal preparations from Neisseria gonorrhoeae

Protection against gonococcal infection was obtained by immunization with ribosomal preparations from Neisseria gonorrhoeae. Ribosomes were isolated from disrupted cells by differential ultracentrifugation and treatment of the microsomal fraction with 0.25% sodium dodecyl sulfate. The isolated ribosomal preparations contained 55% ribonucleic acid, 39% protein, and 0.35% carbohydrate. The ribosomal preparations contained small amounts of endotoxin as determined by thiobarbituric acid- and lead acetate-sensitized mice assays. Guinea pigs immunized subcutaneously with ribosomal preparations were challenged intrachamberially with 10(7) colony-forming units of N. gonorrhoeae, and protection was assessed by clearance of the organism from subcutaneous chambers. The ribosomal preparations elicited significant protection, which was enhanced by incoporation of the immunogen into adjuvant. This protection was comparable to that obtained with whole cells. Treatment with proteolytic enzymes destroyed the protective effect of the ribosomal preparations, but ribonuclease had no measurable effect. Passive hemagglutination and immunodiffusion tests with sera from immunized animals demonstrated the presence of antibody to the ribosomal antigens. Results of adsorption of antiribosomal sera with enzyme-treated ribosomal preparations also indicated the protein nature of the immunogen. These results indicate that protein associated with the gonococcal ribosomal preparation is the major protective immunogen. The role of endotoxin contamination in the immunogenicity of gonococcal ribosomal preparations warrants further investigation.

Immunogenicity of ribosomes from enzymatically lysed Streptococcus pyogenes

Ribosomal fractions isolated from Streptococcus pyogenes by physical and enzymatic disruption of the cell wall were found to provide protection in mice against challenge with the homologous M type. Although ribosomal fractions isolated by physical disruption of the cells also provided protection against challenge with several heterologous M types, ribosomal fractions from enzymatically lysed cells did not provide protection against any of the heterologous M types. Ribosomes isolated by either method were found to be contaminated with cell surface proteins. Chemical analysis of the ribosomes showed a greater protein:ribonucleic acid ratio in ribosomes from physically disrupted cells than in ribosomes from enzymatically disrupted cells (2:1 versus 1:1). Antisera to ribosomes isolated from physically disrupted cells detected many more antigenic determinants on ribosomes isolated from enzymatically disrupted cells than did the corresponding homologous antisera. Immunodiffusion analysis suggested that ribosomes isolated from physically disrupted cells may contain cell wall antigenic determinants which are present on ribosomes isolated from enzymatically disrupted cells in a partially degraded form. Washing of ribosomes in high-molarity salt solutions suggested that some of the contaminating cell wall proteins are tightly bound to the ribosomes.

Correlation of the duration and magnitude of protection against Salmonella infection afforded by various vaccines with antibody titers

Groups of mice were immunized with optimal doses of the following vaccines of Salmonella typhimurium W118-2: acetone-killed cells, lipopolysaccharide, ribosomes, and live cells. At 3 weeks, 1 month, 2 months, 4 months, or 6 months postimmunization, sera were collected from control and vaccinated animals, and the anti-lipopolysaccharide and whole-cell agglutination titers of the sera were determined. Other groups of similarly vaccinated mice were tested for resistance to infection by challenging with live W118-2 and scoring the number of survivors 30 days postinfection. It was found that only ribosomes and live cells afforded significant protection 6 months after immunization. Thus, in duration of protection ribosomes were superior to the other nonviable vaccines tested. At all time intervals tested, purified lipopolysaccharide was the least effective vaccine. Protection afforded by the acetone-killed cell and ribosomal vaccines correlated better with the whole-cell agglutination titers than with the anti-lipopolysaccharide titers. However, the longer duration of protection afforded by the ribosomal vaccine, as compared with the acetone-killed vaccine, could not be accounted for by differences in whole-cell agglutination titers. These studies show that ribosomal vaccines are equal in all parameters to acetone-killed cells and have the advantage of providing longer-lasting immunity.

Immunogenicity of the ribosomal fraction of Salmonella typhimurium: analysis of humoral immunity

The ribosomal fraction prepared from Salmonella typhimurium LT2 was further purified by gel filtration of Sepharose 4B and afforded excellent protection against homologous challenge. The highly effective immunogens were composed of several fractions which could give different types of protection to mice. The first type of protection was heat-labile antigens which could induce humoral immunity, and the second type of protection was heat-stable antigens capable of evoking cellular resistance in mice. The former were different from O-antigens and the latter were free of endotoxin and rich in ribonucleic acid. The third type of protection was heat-resistant substances of cell wall components, which were mainly composed of O-antigens. The high immunogenicity observed in this study could be obtained only by the heat-stable antigens rich in ribonucleic acid, and the immunity conferred by this kind of antigen was due to the cellular type of protection.

Capsular serotypic specificity of the protection conferred on mice by Klebsiella pneumoniae ribosomal preparations

Klebsiella pneumoniae ribosomal preparations protect mice immunized by the subcutaneous route against an intraperitoneal challenge of 100 50% lethal doses. The minimal protective doses are 5 and 0.4 micrograms of proteins for preparations extracted from strains of capsular serotypes 1 and 2, respectively. This difference in protective activity is also found in bacteria killed by Formalin. The protective activity of these preparations is not diminished by their purification on sucrose gradient, which eliminates most of the membrane vesicles which are visible by electron microscopy. The use of four strains of K. pneumoniae belonging to capsular serotypes 1 and 2 allowed us to show that the immunoprotective capacity of the ribosomal preparations was specific to the capsular serotype of the origin strain. This was confirmed by experiments in which the serum of immunized mice was transferred passively. The experimental data favor the presence in the ribosomal preparation of antigens belonging to the bacterial surface and resisting elimination by ultracentrifugation on sucrose gradient. Those surface antigens (possibly capsular polysaccharide) at least play a role in the orientation of the specificity of the protection induced by the ribosomal preparations.

Protective ability of Salmonella ribosomal protein and RNA in inbred mice

Ribosomal vaccines prepared from Salmonella typhimurium were effective immunogens in A/J, C3H/HeDub, and C3H/HeJ mice. Purified ribosomal components were also tested as immunogens in the inbred mice. Protein isolated from a Salmonella ribosomal fraction could protect all three mouse strains. Although purified RNA was shown to be protective for A/J and C3H/HeDub mice, it was not protective for C3H/HeJ mice. Protective immunity could be induced in A/J and C3H/HeDub mice by various immunostimulants. Immunity in C3H/HeJ mice, however, could only be induced by Salmonella ribosomes or protein isolated from the Salmonella ribosomal fraction.

Immuno-stimulation by a ribosomal vaccine associated with a bacterial cell wall adjuvant in humans

We have studied a new vaccine of ribosomal nature associated with glycoprotein cell walls from Klebsiella pneumoniae which served as an immunoadjuvant. Thus vaccine was administered by the aerosol route to working men free of any important disease, especially of respiratory disease. A total of 104 men working for the Commissariat à l'Energie Atomique, all volunteers, were randomly placed into two groups. During the first period, 51 patients (group I) were vaccinated three times a week during 5 weeks, and the second group was used as control. During the second period, which started on day 225, the control group received the vaccine, and the first group was revaccinated. Results of this experience show a significant difference in the immunity of the two groups. The specific antibodies increased with vaccination as illustrated by chi-square test (Yates correction), which corresponds to an independent probability equal to 0 (P = 0.5 X 10-4).

Immunogenic capacity of ribosomes of Salmonella typhi interfered with a flagellin-like material contaminant

The double-immunodiffusion technique and sodium dodecyl sulfate-polyacrylamide electrophoresis were used to demonstrate the presence of flagellin-like material strongly attached to ribosomes of Salmonella typhi Ty 2. This flagellin-like material contaminating the ribosome preparation interferes with the induction of antiribosome serum promoting the formation of antisera reacting either only with flagellin or in some cases with flagellin and ribosomes, but giving a very weak reaction with the latter. The interference is also observed when purified ribosomes from a nonflagellated mutant of S. typhi (S. typhi O-901) mixed with purified S. typhi Ty 2 flagellin are utilized as antigens. The antiribosome sera obtained with ribosomes from S. typhi O-901 have a considerably higher titer than those that are interfered with. These sera were able to react with ribosomes obtained from several related species and did not react with flagella-derived flagellin of S. typhi Ty 2.

Comparative efficacy and toxicity of a ribosomal vaccine, acetone-killed cells, lipopolysaccharide, and a live cell vaccine prepared from Salmonella typhhimurium

The protective and toxic properties of a ribosomal vaccine prepared from Salmonella typhimurium W118-2 were systematicaly compared with those of an acetone-killed whole cell vaccine, purified lipopolysaccharide, and living cells in CD-1 mice. Tests of graded immunizing doses of each vaccine against several challenge doses of live strain W118-2 showed that, although the protection given by ribosomes approached the levels of protection conferred by living organisms, acetone-killed cells administered in appropriate dosages provided levels of protection comparable to that of ribosomes. Lipopolysaccharide was found to be significantly less protective than the other vaccines. On a dry-weight basis, ribosomes were the least toxic with a 50% toxic dose (TD50) of 5,000 microgram; acetone-killed cells had an intermediate TD50 of 1,400 microgram; and lipolysaccharide was the most toxic, with a TD50 of 320 microgram. The dose of each vaccine that protected 50% of the mice against a challenge of 1,00 times the 50% lethal dose was determined and divided by the TD50 to give the therapeutic index. This ratio also indicated that the ribosomes and acetone-killed cells were equally effective, whereas lipopolysaccharide was markedly inferior.

Characterization of the immunoprotective antigen of ribosomal preparations from Haemophilus influenzae

This investigation was designed to characterize the immunoprotective antigen of ribosomal preparations from Haemophilus influenzae. The ribosomes that elicited 80 to 90% protection contained 25% protein and 75% ribonucleic acid but did not contain any detectable hexoses. The immunodiffusion and hemagglutination inhibition tests also failed to demonstrate that the capsular material (polyribose phosphate) was in ribosomal preparations. Treatment of ribosomes with ribonuclease degraded 78% ribonucleic acid but did not affect the immunogenicity of such preparations. The proteolytic enzymes reduced the immunogenicity of ribosomes corresponding to the amount of protein degraded. The protection elicited by ribosomal protein extracted with 2-chloroethanol was comparable to that induced by intact ribosomes. In contrast, the low levels of protection observed by immunization with phenol-extracted ribonucleic acid were dependent on the amounts of contaminating protein. Finally, immunogenicity of ribosomal ribonucleic acid and protein was abrogated by treatment with proteolytic enzymes. These results clearly indicate that the protein associated with Haemophilus ribosomes is the major immunoprotective antigen.

New test for endotoxin potency based upon histamine sensitization in mice

The results of a test of endotoxic potency based upon the development of histamine hypersensitivity in mice were compared with the results obtained by testing the same materials for pyrogenicity in rabbits and lethality for chicken embryos (CELD50). The results of the histamine hypersensitization test (HHT) correlated well with those of the other two tests. The sensitivity of the HHT was about the same as that of the CELD50 assay. The HHT may provide a relatively inexpensive, fast, and reliable assay method for endotoxin laboratories that do not have the facilities for the more elaborate assays.

Role of endotoxin contamination in ribiosomal vaccines prepared from Salmonella typhimurium

Ribosomal vaccines prepared from Salmonella typhimurium SR-11 and 6707 an Re mutant bacterium of strain LT2, were effective immunogens in A/J and C3H/HeDub inbred mice. Only SR-11 ribosomes were able to induce significant protection in C3H/HeJ mice. C57BL/6J mice were not protected by either ribosomal preparation. A/J mice were protected against salmonella infection by purified SR-11 endotoxin preparations. Neither the C3H/HeDub, the C3H/HeJ, nor the C57BL/6J mice were protected by the endotoxin preparation. Passive hemagglutination studies showed that C3H/HeJ mice had no antibodies to O antigen but were significantly protected by SR-11 ribosomes. In contrast, C57BL/6J mice, which had the highest titers of O antibodies of the four inbred mouse strains, were not protected by SR-11 ribosomes. Endotoxin cannot totally account for the effectiveness fo ribosomal account for the effectiveness of ribosomal vaccines prepared from S. typhimurium.

Lack of protection afforded by ribonucleic acid preparations from Mycobacterium tuberculosis against Mycobacterium leprae infections in mice

Mycobacterial ribonucleic acid preparations from H37Ra, an attenuated strain of Mycobacterium tuberculosis, provide their usual marked protection against M. tuberculosis challenge; however, they provided no protection against Mycobacterium leprae challenge. Suspensions of intact H37Ra were not effective against M. leprae. Suspensions of BCG gave their usual distinct protection against M. leprae challenge.

Immunogenic activity of a ribosomal fraction obtained from Pasteurella multocida

The cells of P. multocida strain P-1059 were destroyed with the French pressure cell; the ribosomal fraction proven to be homogeneous by analytical ultracentrifugation was obtained from the product by centrifugal fractionation, zonal electrophoresis, and Sephadex G-200 gel filtration. The ribosomal fraction exhibited intense protective antigenicity in mice and chickens, but the lipopolysaccharide (endotoxin) and the other bacterial cell fraction obtained in this experiment did not. Sodium deoxycholate treatment of the ribosomal fraction resulted in only a 13% loss in immunological activity, and ribonuclease treatment caused a 60% loss of activity.

Variability of protection in inbred mice induced by a ribosomal vaccine prepared from Salmonella typhimurium

Ribosomal vaccines prepared from Salmonella typhimurium were effective immunogens in A/J inbred mice and C3H/HeTex, inbred mice. However, ribosomal vaccines were not protective in C57BL/6J inbred mice. A/J mice were protected against lethal challenge by attenuated S. typhimurium live-cell, ribosomal, phenol, and heat-killed vaccines. C3H/HeTex mice were protected by live-cell, ribosomal, and phenol vaccines but not the heat-killed vaccine. Only the live-cell vaccine gave significant protection in the C57BL/6J inbred mice. A comparison of the kinetics of infection in sham-immunized mice and mice immunized with ribosomes showed that ribosome preparations elicited protection against Salmonella infection in mice inherently sensitive and resistant to Salmonella.

Humoral immunity to Streptococcus pneumoniae induced by a pneumococcal ribosomal protein fraction

Isolation of a protective subfraction of ribosomes from Streptococcus pneumoniae has been achieved, and the immune response it induces has been investigated. Mice immunized with pneumococcal ribosomes or purified protein extracted from the ribosomal preparation (2-CE protein) exhibit similar survival rates upon challenge by virulent S. pneumoniae. In contrast, recipients of purified ribosomal ribonucleic acid were never protected against pneumococcal challenge. Serum from mice immunized with pneumococcal ribosomes or 2-CE protein passively immunized syngeneic recipients against pneumococcal challenge, whereas spleen cells from the same donors were unable to transfer immunity. Passive immunization with antiribosome serum could be abrogated by absorption with whole ribosomes, 2-CE protein, or various serotypes of S. pneumoniae (capsular types 2, 3, 6, and 14). Antiribosome serum significantly enhanced clearance of S. pneumoniae from mouse blood in vivo and in vitro. This required phagocytic cells, since antiribosome serum alone, with or without complement, supported growth of S. pneumoniae to an extent comparable to normal serum. The data suggest that the primary immunogen of pneumococcal ribosomes resides in the protein fraction. Further, the immunity induced by the protein fraction is mediated by antibody that appears to function as an opsonin for S. pneumoniae.

Evidence for an extrinsic immunogen in effective ribosomal vaccines from Salmonella typhimurium

Previous work has indicated that ribosomes isolated from Salmonella typhimurium were highly immunogenic and afforded excellent protection against homologous challenge. Effective protection was obtained also when ribonucleic acid ( RNA) extracted from these ribosomes was used as a vaccine. In this investigation ribosomes prepared by another method and washed repeatedly in 1 M NH1Cl lost much of their prophylactic potency and yielded poorly protective RNA. The high-salt wash of the ribosomes was immunogenic. The RNA and the protein isolated from the salt wash of the ribosomes were effective vaccines. No intrinsic component of the ribosomes was removed by the NH4Cl wash, since the ability of both "crude" and "clean" ribosomes to function equally well in an in vitro protein synthesizing system was demonstrated. The presence of a component with toxic properties similar to those of endotoxin was found in active vaccines but not in weak ones. This was shown by the ability of effective vaccines to kill lead acetate-sensitized mice and to induce tolerance to endotoxin.

The immunogenic activity of ribosomal fractions derived from Brucella abortus

The immunizing activity of ribosome preparations derived from Brucella abortus strain 19 cells was examined in guinea-pigs and mice. After subcutaneous injections of Br. abortus ribosomes in Freund's incomplete adjuvant, both mice and guinea-pigs developed immunity to challenge by virulent Br. abortus 544 organisms which was at least as effective as the protection conferred by live strain 19 vaccine. Both mice and guinea-pigs also developed agglutinating and complement-fixing antibodies and delayed hypersensitivity to Br. Abortus antigens. Conversely, ribosome preparations elicited delayed hypersensitivity reactions on intracutaneous injection into guinea-pigs chronically infected with Br. abortus or Br. melitensis. On injection into rabbits, Br. abortus ribosomes incorporated in incomplete adjuvant induced high titres of agglutinins, complement fxing antibodies and precipitins for Br. abortus antigens. On immunochemical examination, the ribosome preparations were not grossly contaminated with antigens derived from the cell surface. They were chemically complex, however, and in addition to RNA contained numerous protein components identified by disk electrophoresis. The nature of the components responsible for conferring protection against Br. abortus was not determined.

Evidence for O antigens as the antigenic determinants in "ribosomal" vaccines prepared from Salmonella

The nature of the protective substance in ribosomal ribonucleic acid and protein extracts of Salmonella has been investigated. The results of experiments in which vaccines were prepared from isogenic strains and strains with defects in lipopolysaccharide synthesis show that O antigens contaminate both ribonucleic acid and protein ribosomal extracts, and are responsible for at least part of their strain-specific protective activity. In addition, it was observed that a ribosomal ribonucleic acid preparation from S. adelaide contains a heat-stable immunogen which is not an O antigen or that gives cross-protection across species lines. The contribution of ribosomes to the immunity induced by "ribosomal vaccines" is discussed.

Effect of erythrocytes treated with enterobacterial common antigen on experimental Salmonella typhimurium infection of mice

The immunogenicity of enterobacterial common antigen (CA)-treated horse or mouse erythrocytes was determined in Swiss white albino mice by comparing survival rates with control mice, immunized with P. aeruginosa fraction-treated RBC and challenged in parallel with 10 LD50 S. typhimurium. The administration of small amounts of CA on horse, but not mouse, RBC significantly delayed mortality; protection was only marginally less than that evoked with 12-fold larger amounts of CA in the absence of RBC. Survival in infected animals was transient; independent of immunogen or control preparation employed, all mice were dead by day 15 after challenge.

Immunogenicity of ribosomal vaccines isolated from group A, type 14 Streptococcus pyogenes

A ribosomal preparation isolated from group A, type 14 Streptococcus pyogenes protected mice against a challenge of 1,000 mean lethal doses. Optimal immunization consisted of subcutaneous administration of 326 mug of protein with Freund incomplete adjuvant. Animals immunized with higher or lower antigen concentrations showed decreased survival. Freund incomplete adjuvant was necessary to insure optimum immunization. Immunochemical studies showed no M protein or C carbohydrate present in the ribosomal preparation. Mice optimally immunized with the type 14 ribosomal preparation were protected against heterologous challenge with M types 2, 5, 8, and 12. Protein-free ribonucleic acid extracts isolated from the type 14 ribosomal preparation did not protect mice against homologous challenge. But ribonucleic acid-free protein extracts showed 100% protection in mice after homologous challenge.

An analysis of those components of Toxoplasma gondii responsible for delayed hypersensitivity reactions in mice

Testing of extracts of Toxoplasma gondii (RH strain) indicated that delayed hypersensitivity as manifested by delayed skin reactions and inhibition of macrophage migration was induced only by those fractions containing RNA.

Protection against Toxoplasma gondii in mice immunized with Toxoplasma cell fractions, RNA and synthetic polyribonucleotides

Mice immunized with fractions obtained by centrifugation of disrupted Toxoplasma gondii trophozoites as well as with 200 μg of Toxoplasma ribonucleic acid (RNA) were resistant (as measured by time to death and total mortality) to challenge with Toxoplasma 30 days later. When mice were challenged at 15 days no protection was noted. A dose of 50 μg of Toxoplasma RNA was effective in protecting mice against lethal challenge only when incorporated into Freund's incomplete adjuvant. In studies performed to determine the specificity of the resistance observed, resistance was also noted in mice immunized with 200 μg of RNA extracted from normal mouse peritoneal macrophages, as well as in mice immunized with 100 μg of the synthetic polyribonucleotide polycytidylic acid. Polyadenylicuridylic acid conferred protection only when incorporated into Freund's incomplete adjuvant and polyinosinic—cytidylic acid had no effect. The protection induced by Toxoplasma RNA was eliminated by prior treatment of the preparation with ribonuclease but not by treatment with pronase, suggesting that the moiety responsible for the protective effect was RNA. In experiments designed to explore the mechanism of resistance in the vaccinated mice, macrophages harvested from mice which had been injected with Toxoplasma RNA 15 days earlier were found to be activated in that they resisted challenge with Listeria monocytogenes.

Ribosomal vaccines. II. Specificity of the immune response to ribosomal ribonucleic acid and protein isolated from Salmonella typhimurium

Ribosomal proteins isolated from Salmonella typhimurium were effective in inducing immunity in mice. This immunity was specific since animals immunized with ribosomal proteins from S. typhimurium were not protected against challenge with S. cholerae-suis or S. enteritidis. Immunity was evident as early as 5 days after immunization. Ribosomal ribonucleic acid (RNA) failed to provide any effective immunity in mice. Polyinosinic acid: polycytidylic acid (poly I: C) induced a rapid, short-lived immunity to all three Salmonella species. In contrast, ribosomal RNA failed to elicit any rapid nonspecific response to infection.

Immunity to Salmonella typhimurium infection: characterization of antigens in active protection by polyacrylamide gel electrophoresis

Immunity to challenge with Salmonella typhimurium (strain SR-11) was studied in NIH/NMRI Swiss mice. Viable organisms induced the best protection, but ribosomes were the best immunogen of the subcellular fractions. Antigens with lower concentrations of protein did not induce protection as well as antigens which had higher concentrations of protein. Acrylamide gel electrophoresis of the SR-11 subcellular components, fractionation, and differential staining of the gel columns indicated that the immunogen is a high-molecular-weight glycoprotein or mucopolysaccharide.

Ribonucleic acid-protein fractions of virulent Salmonella typhimurium as protective immunogens

Mice were injected with virulent Salmonella typhimurium SR-11 subfractions containing varied amounts of ribonucleic acid (RNA) and protein or with living attenuated S. typhimurium RIA. In these mice, maximal resistance to lethal infection by 1,000 or 5,000 median lethal doses of S. typhimurium SR-11 was seen 2 to 3 weeks after immunization. The S. typhimurium RIA vaccine and a crude ethanol-precipitated RNA fraction (E-RNA) prepared from lysates of S. typhimurium SR-11 were the most efficient immunogens inducing protection against salmonellosis. The contribution of the components present in the E-RNA fractions to host protection against lethal salmonella infection was also examined. RNA-rich fractions (P-RNA) prepared from lysates of the virulent salmonellae contained several bands of protein when examined by disc electrophoresis. P-RNA fractions stimulated protective immunity in mice to infection with S. typhimurium SR-11 but to a much lesser degree than did the E-RNA fractions or strain RIA vaccine. Protein-rich fractions (NP), separated from E-RNA by salt precipitation, exhibited the same number and distribution of protein bands by disc electrophoresis as did the parent E-RNA fractions. Mixtures of either bovine liver soluble RNA or various synthetic polynucleotides and NP were examined, as was NP fraction alone, for the ability to confer protection in mice to challenge infections by the virulent strain of salmonella. Polyadenylic-uridylic acid plus NP conferred significant protective immunity to challenge infections in mice immunized with this mixture, being nearly as effective an immunogen as were the E-RNA fractions of S. typhimurium SR-11 or the attenuated S. typhimurium RIA.

Response of mice to injection of ribosomal fraction from group B Neisseria meningitidis

Ribosomes of strain NOR-7 of group B Neisseria meningitidis were isolated by a procedure that included treatment of the cells with sodium dodecyl sulfate, disruption in a French pressure cell, and differential centrifugation. These preparations consisted of 66% ribonucleic acid and 24% protein and sedimented as a single component with a constant of approximately 66S. When used in immunodiffusion tests with homologous rabbit antiserum, untreated ribosomes formed two precipitin lines, when treated with ribonuclease three lines, and when Pronase-digested only one distinct line. Qualitatively indistinguishable reactions were obtained with the same antiserum and ribosomes from group A meningococci, but no precipitation occurred with those of Escherichia coli. When injected into mice, group B ribosomes elicited an increase in the number of antibody-producing spleen cells demonstrable by the hemolytic plaque technique using unsensitized sheep erythrocytes. Sensitization of the erythrocytes with increasing amounts of supernatant fluid of meningococcal cultures progressively reduced the number of demonstrable plaque-forming cells. Neuraminidase treatment of the erythrocytes increased immune hemolysis, whereas Pronase digestion reduced it. Injected mice were protected against homologous and heterologous meningococcal challenge. Both hemolysis and protection-inducing activities of the ribosomes were unimpaired by ribonuclease, but were reduced by Pronase. It is concluded that the immunological response elicited by the meningococcal ribosomes does not involve the group-specific carbohydrate antigen. The immunological mechanism by which the mice are protected against meningococcal challenge remains unknown.

Isolation of protective somatic antigen from Vibrio cholerae (Ogawa) ribosomal preparations

Ribosomal preparations from Vibrio cholerae Ogawa and Inaba are protective immunogens for mice challenged with either serotype. Column chromatography of ribosomal fractions separated protective antigen from the ribosomes. The antigen is a heterogeneous colloid which contains protein, lipid, and carbohydrate in the ratio 3:1:1. Amino acid composition is that of a slightly acidic protein with no unusual complement of amino acids. The lipid component consists of several longchain fatty acids and of phosphatidyl ethanolamine. The major sugars identified were glucose and galactose. The colloid can be dissolved by treatment with chelating agents and sodium dodecyl sulfate. Purification of the solubilized material or of the colloid was unsuccessful.

Ribosomal vaccines. I. Immunogenicity of ribosomal fractions isolated from Salmonella typhimurium and Yersinia pestis

The immunogenicity of ribosomes and ribosomal subfractions isolated from Yersina pestis and Salmonella typhimurium has been studied. Ribosomes and ribosomal protein isolated from S. typhimurium protected mice against lethal challenge. Ribosomal ribonucleic acid isolated by phenol extraction failed to induce any significant level of protection in mice. None of the ribosomes or ribosomal subfractions isolated from Y. pestis were effective in inducing immunity to lethal challenge. These results suggest that the immunogen of the ribosomal vaccine is protein.

Purification of immunogenically active ribonucleic acid preparations of Salmonella typhimurium: molecular-sieve and anion-exchange chromatography

Immunogenic Salmonella typhimurium ribonucleic acid (RNA) preparations, prepared by differential centrifugation, phenol extraction at 65 C, and ethanol precipitation from 0.5% sodium dodecyl sulfate solution, maintained their immunogenicity through lyophilization. As measured by survival, differential pathogen counts 5 days postchallenge, or clearance of the infecting organism from the tissues, immunization with 50 mug (dry weight) of the lyophilized preparation proved as effective as immunization with 0.1 LD(50) of attenuated S. typhimurium cells. Chromatography of the immunogenic fraction through Biogel P-6 (exclusion limit > 4,600) or through Biogel P-300 (exclusion limit > 300,000) resulted in only one immunogenically active protein of the eluate found in the void volume of the columns. Diethylaminoethyl (DEAE) cellulose anion-exchange chromatography of the RNA preparations showed that the immunogenic activity was eluted from the column at 0.8 to 1.0 m NaCl in a linear 0.1 to 2.0 m NaCl gradient. Nonimmunogenic, protein-containing minor peaks were eluted at 0.1 to 0.5 m NaCl. Serial fractionation of the crude RNA preparations over Biogel P-6 to DEAE cellulose to Biogel P-300 molecular-sieve or anion-exchange columns did not alter the immunogenicity of the RNA preparation. Incorporation of the column fractions into Freund's incomplete adjuvant did not increase their relative effectiveness in eliciting anti-salmonella resistance. Chemical analysis of the immunogenic preparations indicated that they were lacking in detectable protein, lipid, and deoxyribonucleic acid. These results suggest that the immunogenic moiety of the crude nucleic acid fraction is either RNA or an as yet undefined polysaccharide of greater than 300,000 molecular weight.