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

Mouse models to assess the efficacy of non-typhoidal Salmonella vaccines: revisiting the role of host innate susceptibility and routes of challenge

Non-typhoidal Salmonella enterica (NTS) serovars Typhimurium and Enteritidis are important causes of bacterial gastroenteritis in the USA and worldwide. In sub-Saharan Africa these two serovars are emerging as agents associated with lethal invasive disease (e.g., bacteremia, meningitis). The development of NTS vaccines, based on mucosally administered live attenuated strains and parenteral non-living antigens, could diminish the NTS disease burden globally. Mouse models of S. Typhimurium and S. Enteritidis invasive disease can accelerate the development of NTS vaccines. Live attenuated NTS vaccines elicit both cellular and humoral immunity in mice and their efficacy is well established. In contrast, non-living vaccines that primarily elicit humoral immunity have demonstrated variable efficacy. An analysis of the reported studies with non-living vaccines against S. Typhimurium and S. Enteritidis reveals that efficacy is influenced by two important independent variables: (1) the innate susceptibility to NTS infection that differs dramatically between commonly used mouse strains and (2) the virulence of the NTS strain used for challenge. Protection by non-living vaccines has generally been seen only in host-pathogen interactions where a sub-lethal infection results, such as challenging resistant mice with either highly virulent or weakly virulent strains or susceptible mice with weakly virulent strains. The immunologic basis of this discrepancy and the implications for human NTS vaccine development are reviewed herein.

Inactivated and subunit vaccines to prevent shigellosis

Shigellosis remains a formidable disease globally, with children of the developing world bearing the greatest number of infections. The need for an affordable, safe and efficacious vaccine has persisted for decades. Vaccines to prevent shigellosis can be divided into living and nonliving approaches. Several nonliving Shigella vaccines are currently at different stages of development and show substantial promise. Outlined here is an overview of multiple nonliving vaccine technologies, highlighting their current status and recent advances in testing. In addition, gaps in the knowledge base regarding immune mechanisms of protection are explored.

Immunotherapy of a plasmacytoma with attenuated salmonella

An attenuated strain of Salmonella typhimurium, SL3235, developed as a prototypic typhoid vaccine, is shown to retard growth of a murine plasmacytoma, TEPC-183, and to prolong survival of tumor-bearing mice. Live salmonella, but not acetone-killed organisms, had antitumor activity. The immunotherapeutic effect was demonstrable when the tumor was injected intralesionally or intraperitoneally. Increased survival, longer mean time to death, and retardation of tumor growth were found when the salmonella were given intralesionally as late as the sixth day post-tumor injection. Timing of salmonella inoculation, as well as the salmonella dose, had an effect on treatment efficacy. Injection of salmonella intraperitoneally exerted a strong antitumor effect when given as late as the third day post-tumor inoculation. The highest dose (2 x 10(6)) of salmonella was less effective than doses 10- or 100-fold lower. TEPC-183 plasmacytoma is rapidly growing and highly immunosuppressive, so the ability of the salmonella to exert therapeutic activity against it is a measure of the potency of the vaccine. These observations are of interest, as they show that a genetically engineered, avirulent strain of Salmonella has immunotherapeutic properties similar to those of BCG and other biological response modifiers, and might have clinical potential as an antitumor agent.

Protective capacity of L-form Salmonella typhimurium against murine typhoid in C3H/HeJ mice

L forms of Salmonella typhimurium LT2 conferred strong protection to a lethal challenge with its parental bacterium on innately hypersusceptible C3H/HeJ mice, and its minimal protective dose was approximately 150 L-forming units. Although L-form S. typhimurium was avirulent for C3H/HeJ mice, it multiplied slowly in both the liver and spleen with the maximal growth 2-3 weeks after immunization and thereafter it persisted in the liver until 24 weeks. Protective immunity began to work between 4 and 6 weeks after immunization, and it remained active as long as the L forms colonized the liver (until 24 weeks after immunization). Vaccination with the L form induced a population of T cells responding to L-form whole-cell lysate (WCL), while delayed-type hypersensitivity (DTH) to the extract of S. typhimurium was induced after the establishment of solid immunity. Moreover, neither T-cell responses nor DTH to heat-killed S. typhimurium was generated. In addition, antibody responses were elicited to WCL but not to heat-killed S. typhimurium. These results indicate that protection conferred by the L forms is attributable to the persistent colonization of the L forms rather than the presence of DTH, and also that Salmonella cytoplasmic antigens are involved in induction of immunological responses by vaccination with the L forms.

A protective role of extrathymic alpha beta TcR cells in the liver in primary murine salmonellosis

The liver comprises unique T cells differentiating extrathymically and expressing an intermediate intensity of alpha beta T-cell receptor (TcR) and a high intensity of leucocyte function antigen-1 (LFA-1). To elucidate the functional roles of the intermediate alpha beta TcR cells in host defence against bacterial infection, we examined the effects of depletion of the intermediate alpha beta TcR cells by in vivo administration of monoclonal antibodies (mAb) to intercellular adhesion molecule-1 (ICAM-1)/LFA-1 and alpha beta TcR on the bacterial growth in the liver after infection with Salmonella chorelaesuis in mice. Pretreatment with mAb to LFA-1 (200 micrograms/mouse) together with mAb to ICAM-1 (200 micrograms/mouse), which could preferentially deplete the intermediate alpha beta TcR cells and gamma delta TcR cells in the liver, resulted in a severely reduced ability to resolve acute phase of Salmonella infection in the liver. Pretreatment with a low dose of anti-alpha beta TcR mAb (60 micrograms/mouse), which depleted only bright alpha beta TcR cells, did not affect the bacterial growth in the liver at the early stage after Salmonella infection, while the depleting of both intermediate and bright alpha beta TcR cells by pretreatment with a high dose of anti-alpha beta TcR mAb (120 micrograms/mouse) allowed the bacteria to multiply exaggeratedly in the liver at this stage. These results suggest that intermediate alpha beta TcR cells may play an important role in protection at the early stage after Salmonella infection in liver and that the interaction of ICAM-1/LFA-1 is critically involved in protective roles of extrathymic T cells bearing intermediate alpha beta TcR in liver at the early stage after Salmonella infection.

Correlation of antibody titres induced by vaccination with protection in mouse typhoid

The ELISA method was used to titrate the humoral immune response in vaccinated mice. When mice were given two doses of a heat-killed salmonella vaccine 6 days apart, there was a steady but low-level increase of antibody synthesis. In contrast, if a booster vaccination was administered 21 days after the primary inoculation, the anamnestic response produced a significantly greater antibody titre, rapidly reaching its peak within 10 days. Such a heightened humoral response induced in the genetically susceptible C57BL/6J mice also coincided with effective protection against an otherwise lethal challenge with Salmonella typhimurium.

Induction of gamma/delta T cells in murine salmonellosis by an avirulent but not by a virulent strain of Salmonella choleraesuis

To elucidate the relationship between the virulence of intracellular bacterium and its ability to induce gamma/delta T cells in the host during infection, we examined the differences in appearance of gamma/delta T cells in mice infected with Salmonella choleraesuis virulent strain RF-1 carrying a virulence plasmid of 50 kb, and with avirulent strain 31N-1 cured of the 50-kb plasmid. The number of gamma/delta T cells in the peritoneal cavity was increased to a significant level on day 3 after an intraperitoneal infection with a sublethal dose (5 x 10(4) colony-forming units) of avirulent strain 31N-1. On the other hand, no increase in the number of gamma/delta T cells was evident in the peritoneal cavity at any stage after infections with various doses of virulent strain RF-1, although the numbers of the bacteria were drastically increased. Similar to that seen in the peritoneal cavity, the number of gamma/delta T cells in the liver was significantly increased after an intraperitoneal infection with avirulent strain 31N-1 but not with virulent strain RF-1. The early appearing gamma/delta T cells during salmonellosis with avirulent stain 31N-1, which preferentially used V gamma 1/V delta 6, showed blastogenesis in response to purified protein derivative (PPD) derived from Mycobacterium tuberculosis. The gamma/delta T cells also responded to the peritoneal adherent cells in mice infected with avirulent strain 31N-1 6 d previously, which expressed a high level of endogenous heat-shock protein (hsp) homologous to the mycobacterial 65-kD hsp. The expression of the hsp, however, was not prominent in the adherent cells in mice infected with virulent strain RF-1. These results suggest that the gamma/delta T cells specific for PPD may play important roles in host defense against murine salmonellosis, and that the virulence of Salmonella may be inversely correlated with its ability to induce endogenous hsp in the infected macrophages, which in turn stimulate the gamma/delta T cells in the host during salmonellosis.

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.

Yersinia enterocolitica serotype O:3 is arthritogenic for mice

It is shown, for the first time, that Yersinia enterocolitica serotype O:3 is experimentally arthritogenic. Moreover, it is arthritogenic for the mouse, an optimal model for human yersiniosis. This arthritis can be induced by the oral route, the most common route in man. The pattern of joint disease closely parallels that of human reactive arthritis associated with this pathogen.

Pathogenesis and immunity in murine salmonellosis

Salmonella is traditionally described as a facultative intracellular parasite, and host macrophages are regarded as the primary effector cells in both native and acquired immunity in mouse typhoid. This concept has not been unanimously accepted in the literature. Based on cell culture experiments and electron microscopic examinations of infected tissues, we observed that virulent Salmonella typhimurium is killed within polymorphs and macrophages of guinea pigs and mice. In a systemic disease, the organism propagates primarily in the extracellular locations of sinusoids and tissue lesions and within hepatocytes. Hence, it is more likely to be an extracellular pathogen and its virulence is directly related to its antiphagocytic property. The conspicuous absence of macrophages in the primary lesions of murine salmonellosis disputes the likelihood of their significant role in native resistance to the disease. Acquired cellular immunity is expressed as an enhanced antibacterial activity of macrophages facilitated by cytophilic antibodies rather than as an altered antibacterial action of immune macrophages. It is proposed that acquired immunity in murine salmonellosis is a synergistic manifestation of the innate capacity of polymorphs and macrophages to destroy ingested salmonellae, the activated antibacterial functions of macrophages mediated by cytophilic antibodies, the opsonic and agglutinating actions of antiserum, and the accelerated inflammation associated with delayed hypersensitivity to bacterial antigens. Unlike live attenuated vaccines, nonviable vaccines offer a significant, though not a solid, protection against subsequent challenges.

Immunogenic endotoxin associated protein from a rough strain of Salmonella

A multimolecular complex of polypeptides found associated with the lipopolysaccharide endotoxin in Salmonella, referred to as endotoxin-associated protein (EP), has been extracted from a rough strain of Salmonella typhimurium which does not synthesize 0 antigens. Since standard methods of extraction applicable to smooth strains of Salmonella were not successful for this rough strain, two modified procedures were developed. The resulting products were similar to smooth EP in terms of their biochemical, physical and mitogenic properties. When the immunogenicity of the rough EP was characterized by a protection assay in mice challenged with virulent Salmonella, it was found that the rough EP preparations were protective; however, they were not as active as the EP from a smooth strain of S. typhimurium.

Enhancement of protection against Salmonella infection in mice mediated by a synthetic lipopeptide analogue of bacterial lipoprotein in S. typhimurium vaccines

Vaccines consisting of acetone-killed Salmonella typhimurium were supplemented with a synthetically prepared lipopeptide derivative of bacterial lipoprotein, Pam3Cys-Ser-Ser-Asn-Ala. NMRI mice were immunized with these vaccines, receiving two intraperitoneal injections and were challenged intraperitoneally with graded doses of S. typhimurium C5. The protective capacity of the supplemented vaccines was compared with that of the unsupplemented bacterial vaccine, and with the effectiveness of the supplementing component alone. The LD50 served as a criterion for protective capacity. The results showed that 90% of the S. typhimurium S-form vaccine could be replaced by the adjuvant lipopeptide without a recognizable decrease in protective immunizing capacity. A similar but less pronounced enhancement of protection was obtained with a R-mutant vaccine supplemented with the lipopeptide; by supplementing the standard vaccine dose with lipopeptide an increase in protection was also achieved. Lipopeptide alone was not effective in protecting mice from infection with S. typhimurium.

Isolation and immunological characterization of a 55-kilodalton surface protein from Salmonella typhimurium

Surface proteins of different Salmonella R mutants were labeled selectively by treating live bacteria with cycloheptaamylose-dansylchloride. The labeled proteins were extracted from the cells with 6 M urea and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. From the urea extract a 55-kilodalton protein common to numerous Salmonella strains could be isolated by ion-exchange chromatography and gel filtration free of lipopolysaccharide. Immunization of rabbits with isolated protein led to the formation of specific antibodies. Such antiprotein antisera could be employed in Western blots for the specific identification of the 55-kilodalton protein in bacterial extracts containing mixtures of different Salmonella proteins. The importance of this antigen is emphasized by antisera against acetone-killed Salmonella bacteria, showing a preferential interaction with the 55-kilodalton protein in Western blots. Active immunization of mice with the 55-kilodalton protein afforded significant protection against experimental infection with S. typhimurium.

Reduced proliferative response of mouse spleen cells to mitogens during infection with Salmonella typhimurium or Listeria monocytogenes

A significant reduction in the mitogenic responsiveness (uptake of 3H-thymidine) of murine spleen cells to concanavalin A, phytohemagglutinin or lipopolysaccharide was observed during infection with virulent Salmonella typhimurium. The decreased response to mitogens could be observed independent of the immunity to typhimurium (Ity) genotype, i.e. in CBA/J mice and C3H/HeJ mice (Ityr) as well as in C57BL/6 mice (Itys). Because reduced responsiveness was demonstrated in C3H/HeJ mice, which are susceptible to S. typhimurium infection but are unresponsive to lipopolysaccharide, it is concluded that the two phenomena are not correlated with one another. A similar decrease in response to mitogens was shown in mice infected with Listeria monocytogenes. Reduction in mitogenic responsiveness was directly correlated with the number of viable bacteria detected in the spleen cell suspension. Decreased lymphoproliferation could be observed as early as 2 days after infection and lasted 3 weeks in sublethally infected mice. The question remains whether or not the reduced responsiveness indicates an enhanced susceptibility to infection or merely represents a high degree of activation of defense mechanisms.

Protective immunity in mouse salmonellosis: comparison of smooth and rough live and killed vaccines

Protective immunity against Salmonella infection was studied in a mouse model. To study specificity of protection we used smooth (O-4,5,12) and rough vaccines; live and killed vaccines of both types were compared. The protection was assessed by enumerating the number of bacteria in the livers, and by following survival of the mice after intravenous challenge with smooth O-4,5,12 bacteria. Passively transferred antibodies induced by the smooth vaccines had a small protective effect and those induced by the rough vaccines no protective effect in this model. Both live vaccines induced long-lasting protective immunity which was much stronger than that mediated by antibodies. Since the live rough vaccine induced protective immunity and contained no O antigen we conclude that the protective immunity induced by it was mainly cell-mediated and directed to other antigens than the O antigen, the target of protective antibodies. Both killed vaccines also induced protective immunity, but this was weaker than that induced by the corresponding live vaccine.

Temperature-sensitive growth mutants as live vaccines against experimental murine salmonellosis

Temperature-sensitive growth mutants of Salmonella enteritidis, NUB 209 and NUB 323, characterized as protein synthesis mutants, were unable to proliferate at 37 C and lost the parent's virulence. In mice, these mutants conferred high levels of protection as live vaccines. Although the vaccination effect of NUB 323 was not so good as that of NUB 209, NUB 323 was preferred as a safer live vaccine because this mutant was completely avirulent and no back mutation appeared.

Analysis of immunity to infection with Salmonella typhimurium in outbred mice. II. Isolation and immunogenicity of the protective non-O antigenic component from ribosomal vaccine

The active component in crude ribosomal fraction (CRF) of Salmonella typhimurium, capable of inducing protective antibody, was partially purified by two series of chromatography (Sephadex G-150 and DEAE-Sepharose CL6B) after sodium dodecyl sulphate (SDS)-treated CRF was precipitated with ammonium sulphate. The major active component was eluted by 0.4-0.45 M NaCl from DEAE-Sepharose CL6B, and its molecular weight was 43,000 as determined by SDS-polyacrylamide gel electrophoresis. Immunization with the fraction containing 43,000 component alone did not always confer protection on CF1 mice, but its administration together with either the purified transfer RNA (tRNA) or Freund's complete adjuvant (FCA) was much more effective against infection with S. typhimurium. Antibody to the fraction containing 43,000 component was not only free in serum but also associated with peritoneal cells. Macrophages that had been exposed to the antibody had enhanced anti-bacterial activity. Western blot analysis showed that 43,000 component did not react to antiserum to lipopolysaccharide (LPS), but to antiserum to CRF. The antibody elicited by non-O antigenic component and the cell-mediated resistance stimulated by the adjuvant effect of RNA together confer effective protection on CF1 mice.

Protective immunity induced by outer membrane proteins of Salmonella typhimurium in mice

Outer membrane proteins (OMP) extracted from both smooth (C5) and rough (Rb2) strains of Salmonella typhimurium were able to induce protective immunity to salmonellosis. The OMP-induced protection lasted for at least 6 months. The antibody level was estimated by passive hemagglutination. In the C5 OMP-immunized mice, antibodies to both proteins and lipopolysaccharide were detected. On the other hand, in the Rb2 OMP-immunized mice, antiprotein but not antilipopolysaccharide antibodies were detected. Delayed-type hypersensitivity appeared as early as the second week after immunization with OMP and persisted through the fourth week.

Clonal analysis of primary B cells responsive to the pathogenic bacterium Salmonella typhimurium

In the present study, a modification of the splenic focus system is used to analyze the S. typhimurium strain TML (TML)-specific B cell repertoire. The results show that the frequency of primary TML-specific splenic B cells in CBA/Ca mice is approximately 1 per 10(5) B cells and less than 30% of these B cells are specific for LPS. In contrast, the frequency of memory TML-specific cells is approximately 1 per 5-8 X 10(3) splenic B cells and greater than 95% of these B cells are specific for LPS. These results suggest that the frequency of primary TML-specific B cells is extremely low and that it expands 15-20-fold after antigen exposure. It is interesting that less than 30% of the primary B cells are specific for the LPS molecule since it is considered to be the major antigenic determinant on Salmonella organisms. Furthermore, the majority of the LPS-specific anti-TML antibody-producing clones are directed against the LPS O antigen region. Conversely, more than half to two-thirds of the memory LPS-specific anti-TML B cell clones are directed against the KDO or lipid A region of the LPS molecule. These results indicate that the preferential expansion of LPS-specific B cell clones observed after immunization resides primarily in the B cell subsets responsive to the KDO/lipid A moieties on the LPS molecule. Finally, unlike B cell responses to chemically defined antigens, TML stimulates very little IgG1 antibody. IgG2 and IgA isotypes appear to play a predominant role in anti-TML antibody responses, although all H chain classes are produced to some extent. Collectively, these findings are consistent with the responses reported for two other natural antigens, HA and PC. Hence, the pattern of stimulation by infectious agents, such as S. typhimurium, appears to be distinct from that of synthetic antigens. Thus, the studies presented herein have begun to provide insights into those subsets of B cells responsive to S. typhimurium and other infectious disease organisms.

Vaccination of calves with a diaminopimelic acid mutant of Salmonella typhimurium

The purpose of this study was to evaluate the safety and efficacy of a diaminopimelic acid mutant of Salmonella typhimurium as a vaccine for calves. Transposon techniques were used to create a stable nonreverting diaminopimelic acid mutant of a virulent S. typhimurium strain. Calves were vaccinated at weekly intervals with the diaminopimelic acid mutant given as an oral dose of 10(10) organisms, followed by two subcutaneous doses of 10(9) organisms. The calves tolerated vaccination well and the vaccine strain was eliminated from the feces within four days. Of five vaccinated calves, three survived challenge with 5 X 10(9) organisms of the parent strain whereas all five unvaccinated calves that were challenged died. The surviving calves eliminated the challenge organism from the feces within three weeks.

Cellular aspects of the longer-lasting immunity against mouse typhoid infection afforded by the live-cell and ribosomal vaccines

In order to compare the potential of salmonella vaccines prepared from Salmonella typhimurium to provide the longer-lasting protection from the aspects of cell-mediated immunity, groups of mice were immunized with optimal doses of the following preparations: live cells, ribosome-rich extract, acetone-killed cells, and heat-killed cells. At various intervals post-immunization, mouse peritoneal macrophages and splenic T cells were tested for biological activities. The capacity of each vaccine to confer mouse protection against a lethal challenge with S. typhimurium correlated with the degree of macrophage activation engendered by each of them in the early stage of immunization. In the late stage of immunization, the level of mouse protection conferred by each vaccine was found to be based on the capacity of T cells to respond to salmonella antigens, which correlated with the degree of adoptive immunity by T cells. The live-cell and ribosomal vaccines were superior to killed-cell vaccines in inducing the cell-mediated protection. Thus, the longer-lasting immunity provided by the live-cell and ribosomal vaccines can be accounted for by the fact that T cells of mice immunized with both vaccines have the persistent reactivity to salmonella antigens.

Immunomodulation of the antibody response to lipopolysaccharide in C3H/HeJ mice by complexing with heterologous ribosomes

We show that formaldehyde fixation of Salmonella typhimurium lipopolysaccharide (LPS) to ribosomes purified from Brucella abortus induced a primary immunoglobulin M (IgM) response to LPS in C3H/HeJ mice and upon revaccination resulted in elevated titers of IgM and induction of IgG antibody to the O antigens of LPS, as measured by an enzyme-linked immunosorbent assay. A similar LPS-Aspergillus fumigatus ribosomal complex yielded IgM and IgG antibody to LPS only after secondary stimulation. These results demonstrate that the hyporesponsiveness of C3H/HeJ mice with respect to antibody formation to LPS can be overcome by complexing this molecule to ribosomal particles and provide a theoretical mechanism for the action of some "ribosomal" vaccines. The results are compatible with the hypothesis that LPS in complex with the ribosomes is converted to a T-dependent form of the antigen to which the C3H/HeJ mice can respond.

Immunity to Salmonella typhimurium infection in C3H/HeJ and C3H/HeNCrlBR mice: studies with an aromatic-dependent live S. typhimurium strain as a vaccine

Immunization with avirulent Salmonella typhimurium strain SL3235, a smooth, aroA- derivative, was shown to induce high levels of resistance to challenge with virulent S. typhimurium in innately hypersusceptible C3H/HeJ mice and inherently resistant C3H/HeNCrlBR mice. Strain SL3235 is one of a class of avirulent aroA- derivatives made from various strains and species of Salmonella that are being considered as vaccine candidates for cattle and humans. This paper supports their efficacy and potential utility in this regard. In C3H/HeJ mice, immunity against over 1,000 50% lethal doses of virulent S. typhimurium was evident as early as 3 days after immunization and persisted for at least 7 months. Further, the vaccine was effective over a broad spectrum of doses, ranging from 10(4) to 10(6) organisms. Infection with SL3235 led to marked splenomegaly in both mouse strains. The relationship of splenomegaly to the growth kinetics and colonization by SL3235 in the spleens of infected C3H/HeJ and C3H/HeNCrlBR mice was followed. SL3235 initially multiplied slowly in the spleens of both mouse strains and then was rapidly cleared. Less multiplication was seen in the resistant C3H/HeNCrlBR mice than in C3H/HeJ mice. Maximum splenomegaly occurred after clearance of the organism had begun. Protection against virulent S. typhimurium persisted after virtually all of the SL3235 vaccine strain had been cleared from the spleen. Cross-protection against Listeria monocytogenes was evident, but had a later onset, waned by 21 days, and was not detectable by 1 month after vaccination. Demonstration of this cross-protection is consistent with the interpretation that SL3235 induces cellular immunity. One-week immune spleen cells adoptively transferred anti-S. typhimurium and anti-L. monocytogenes immunity. T cell-enriched fractions were ineffective in adoptive transfer, as were spleen cells taken 2 weeks or later after immunization. Protective capacity was in the adherent cell fraction and seemed to be associated with macrophages. Evidence for induction of a population of sensitized T cells was obtained by using a peritoneal exudate T-lymphocyte proliferation assay on peritoneal T lymphocytes collected 1 to 3 months after SL3235 infection.

Macrophage-mediated mitogenic suppression induced in mice of the C3H lineage by a vaccine strain of Salmonella typhimurium

Salmonella typhimurium, strain SL3235, an avirulent organism, has been used as a live vaccine in mice of the C3H lineage and has been found to confer high levels of protection. In the present study, it was found that intraperitoneal injection of approximately 5 X 10(5) live SL3235 induced potent suppression of spleen cell mitogenic responses to a panel of B- and T-cell mitogens in the Salmonella-hypersusceptible C3H/HeJ and C3HeB/FeJ, and the inherently resistant C3H/HeNCrlBR mice. Maximal suppression (greater than 99%) was seen at 1 week, and was still significant but waning (50%) at 3 weeks postimmunization. In contrast, cells of mice receiving acetone-killed cells were not suppressed. Removal of macrophages, but not T or B cells, restored responsiveness, indicating that suppression was macrophage mediated. Prostaglandins were not the major mediator of suppression, as in vitro administration of indomethacin failed to abrogate suppression. As mitogenic suppression occurred in mice with high levels of Salmonella immunity, the suppression is interpreted as a marker of a powerful immunomodulatory process induced by live cells, rather than as an indication of poor immune status of the host.

Role of outer membrane proteins in immunity against murine salmonellosis--1. Antibody response to crude outer membrane proteins of Salmonella typhimurium

The humoral immune response to crude outer membrane proteins (comp) of S. typhimurium in mice has been characterized. Maximal and quicker antibody response was observed when 50 micrograms of comp was injected intraperitoneally. The comp of smooth C5 strain of S. typhimurium evoked antibody response to both lipopolysaccharide (LPS) and proteins. Absorption of these sera with LPS coated erythrocytes eliminated the antibodies to LPS completely, while the antibody level to protein was left unaltered. The comp from rough mutant (lacking O-specific chain of LPS) of S. typhimurium elicited antibodies to proteins but not to LPS. These results indicate the concomitant production of antibodies to Salmonella outer membrane proteins also. The significance of such antibodies in protection and diagnosis has been discussed.

Role of the polysaccharide and of the lipopolysaccharide in the immunoprotective capacity of Klebsiella pneumoniae ribosomes

Ribosomes, ribosomal RNA (r-RNA), capsular polysaccharide (PS-K) and lipopolysaccharide (LPS) were isolated and purified from Klebsiella pneumoniae, type I. The protective capacity of these different fractions was investigated in function of their analytical composition. The results show that ribosomes, and in particular, ribosomal RNA have the greatest protective activity at the lowest concentrations. The role of PS-K in the specific immune response to ribosomes was also investigated. Even at very high levels PS-K failed to afford any significant protection. LPS gave no protection. A stable r-RNA/PS-K complex was isolated by means of affinity chromatography. This complex was uncontaminated by LPS and its existence indicated strong bonding between surface polysaccharide antigens and r-RNA. The r-RNA/PS-K complex was not antigenic in itself but conferred good protection when combined with an adjuvant.

Immunogenic dialyzable factor derived from a ribosomal fraction of Salmonella typhimurium. II. Isolation and characterization of the protective moiety in the dialyzable factor

An immunogenic dialyzable factor was obtained by dialysis of the freeze-thawed ribosomal fraction derived from a smooth virulent strain (LT2) of Salmonella typhimurium. Ion exchange chromatography of the dialyzable factor on Dowex 1-X2 (Cl- form) demonstrated the presence of four peaks and the fourth peak eluted with 0.4 M NaCl in 0.005 N HCl was found to be necessary for protection. This effective peak was not obtained by chromatography of nonprotective dialyzable factors such as an RNase digest. Dowex chromatography of the dialyzable factors isolated from rough mutants of strain LT2 revealed that the dialyzable factor of strain SL1004 whose live vaccine is capable of inducing protective immunity contained fairly large amounts of peak IV. DEAE-cellulose for two-dimensional thin layer chromatography was used to identify the composition of the dialyzable factor and peak IV. Eight spots were located under ultraviolet light and seven spots were characterized by their absorption ratios. In peak IV, four nucleotides were located and identified by comparison with a map of the original dialyzable factor. The data show that the effective components of the dialyzable factor are mixed nucleotides and may be unique to ribonucleic acids of strains of S. typhimurium in which live vaccines are capable of affording mouse protection.

Immunity to Salmonella infection

The foregoing literature review and data presentation have been set forth in the hope of clarifying some complex and confusing issues in regard to Salmonella infection. From a practical point of view, the information presented has implications for the direction to take with regard to improving the current typhoid vaccine, as the presently used acetone-killed cell preparation has considerable toxicity. The issues are important from a theoretical standpoint, because they have bearing on the nature of the concepts researchers and clinicians carry as working hypothesis with regard to the mechanisms of immunity to Salmonella infection. An incomplete appreciation of the literature seems to have led many scientists to believe that only cellular immunity can protect a mouse, and by analogy a human, against Salmonella. The logical deduction from such a premise is that only live vaccines will be effective in humans againsT S. typhi. Such a conclusion would appear unfounded, as documented in this review, for killed vaccines have been shown to be highly effective in vaccinating many mouse strains, as well as humans, against enteric fever.

The protein-lipopolysaccharide complex extracted with trichloracetic acid from Salmonella typhimurium effective in protection of mice against S. typhimurium infection

A protein-lipopolysaccharide complex has previously been postulated as necessary to protect susceptible mice against Salmonella typhimurium infection. Lipopolysaccharide attached to non-specific proteins, bovine serum albumin or methylated BSA, gave a specific delayed-type hypersensitivity (DTH) reaction when injected into the footpad of mice sensitized with sublethal doses of S. typhimurium. However, immunization of BALB/c mice with the complex gave no survivors after challenge with 100 LD50 S. typhimurium. Trichloracetic acid extraction of bacterial cultures produced lipopolysaccharide with attached protein. This method gave simple and convenient production of an active factor, demonstrating few major protein bands after electrophoresis. The complex elicited specific DTH reactions in sensitized mice and protected 37% of BALB/c mice against 100 LD50 S. typhimurium. Combinations of protein:lipopolysaccharide were used in DTH experiments to determine the relative importance of the components. A minimum requirement for both was demonstrated, although the ratio was not critical. Use of O-antigenic mutant strains of Salmonella indicated a role for protein in the specificity of activity of the complex.

Dissociation of innate susceptibility to Salmonella infection and endotoxin responsiveness in C3HeB/FeJ mice and other strains in the C3H lineage

Studies of various mouse strains in the C3H lineage have shown that there is no correlation between innate susceptibility to Salmonella infection and sensitivity to the toxic or mitogenic effects of lipopolysaccharide (LPS). C3H/HeNCrlBR mice were Salmonella resistant, but sensitive to the toxic and mitogenic effects of LPS, whereas C3HeB/FeJ mice were Salmonella susceptible as the C3H/HeJ mice, yet were mitogenically responsive to LPS and sensitive to its lethal effects. Furthermore, other mouse strains (C3H/HeTex and C3H/HeDub) displayed intermediate susceptibility to Salmonella infection and were responders to the mitogenic and toxic effects of LPS. These results are interpreted to mean that endotoxemia cannot be a major factor in the pathogenesis of Salmonella infection and provide evidence for the involvement of multiple factors in the control of innate resistance to Salmonella infection in mice of the C3H lineage.

Phagocytosis and killing of salmonella typhimurium by peritoneal exudate cells

Normal peritoneal cells from conventional, germfree, or nu/nu mice readily killed opsonized salmonellae, an observation that suggests that this activity in the normal peritoneal cavity may not be dependent on either environmental antigenic stimulation or T-cell mediation. In contrast, peritoneal cells elicited 4 days after injection with thioglycolate medium failed to kill opsonized salmonellae but appeared to be highly phagocytic. Peritoneal cells from thioglycolate-treated mice could be induced to kill opsonized salmonellae by giving the mice a primary footpad injection and a secondary intraperitoneal injection of Corynebacterium parvum. This activation by C. parvum appeared to be thymus dependent, since it did not occur in nu/nu mice.

Induction of immunoenhancing factors for murine splenocyte cultures by Salmonella typhimurium ribosome and ribonucleic acid extracts

Ribosomal and ribonucleic acid (RNA)-rich preparations derived from Salmonella typhimurium were examined for their ability to enhance the primary in vitro antibody response of normal mouse spleen cell cultures to sheep erythrocytes. Both of these fractions were consistently more active in elevating the antibody response of normal mouse splenocytes from lipopolysaccharide (LPS) responder mice than was LPS. Furthermore, injection of mice with either the ribosomal or RNA-rich fraction induced antibody response helper factor activity in 2-h post-treatment serum similar to that induced by LPS. Endotoxin low-responding C3H/HeJ mice were stimulated to release helper factors by ribosomes and the RNA extracts but not by LPS. Treatment of the ribosomes and RNA fractions with ribonuclease destroyed their ability to stimulate the production of the helper factor in serum of treated mice. Therefore, it appears likely that ribosomes and RNA-rich fractions stimulated an intermediate helper factor due to the presence of RNA and not LPS.

Artificial Salmonella vaccines: Salmonella typhimurium O-antigen-specific oligosaccharide-protein conjugates elicit protective antibodies in rabbits and mice

Several saccharides representative of the O-antigenic polysaccharide chain of Salmonella typhimurium (O antigens 4 and 12) were used as haptenic groups covalently linked to bovine serum albumin. The disaccharide abequose 1 --> 3 D-mannose was synthesized, and the [Formula: see text] tetra-, octa- and dodecasaccharides were isolated after cleavage of isolated S. typhimurium O-polysaccharide chains by using bacteriophage endo-glycosidases. Rabbits immunized with the saccharide-protein conjugates suspended in Freund complete adjuvant readily responded with O4 antibody titers as high, or almost as high, as those elicited by heat-killed bacteria. The octa- and dodecasaccharide conjugates also gave rise to O12 antibody titers. The antibody response in mice differed in two ways from that seen in rabbits: mice did not respond with measurable antibody production against the disaccharide haptens, and the highest S. typhimurium lipopolysaccharide antibody response elicited by the saccharide haptens was still approximately 50-fold lower than that elicited by heat-killed bacteria. The latter difference may be a consequence of the fact that the mouse preferentially produces antibodies against the galactose residue which is terminal in the hapten but not in the native O-antigenic polysaccharide chain. Antibodies elicited in rabbits against all saccharide-protein conjugates protected passively transferred mice against intraperitoneal challenge with 100 times the 50% lethal dose of S. typhimurium SH 2201 (O4, 12) but not against challenge with S. enteritidis SH 2204 (O9, 12). The antibodies elicited by the saccharide-protein conjugates protected as well as antibodies elicited by heat-killed bacteria.

Evidence for the presence of lipopolysaccharide in a ribonuclease-sensitive ribosomal vaccine of Pseudomonas aeruginosa

To obtain information about the nature of the immunogens in the ribosomal vaccine (fraction II) of Pseudomonas aeruginosa, we studied the specificity of rabbit antibodies to fraction II. Crossed immunoelectrophoresis demonstrated the presence of antibodies which precipitated with ribosomal antigens, but not with lipopolysaccharide (LPS). By means of an enzyme-linked immunosorbent assay, antibodies to LPS were detected in antibodies to fraction II. Antibodies to fraction II could protect mice against a lethal challenge with P. aeruginosa. Absorption experiments demonstrated that the protective ability of antibodies to fraction II was due to antibodies to cell envelope antigens, whereas antibodies to ribosomal antigens did not contribute to the protection. Antibodies to LPS could be detected in mice 1 week after a single vaccination with fraction II. It was concluded that the protective activity of fraction II was due, at least in part, to the presence of LPS in the ribosomal vaccine. Treatment of fraction II with ribonuclease decreased the protective activity of the ribosomal vaccine. Addition of synthetic polyadenylic acid-polyuridylic acid restored the protective activity of ribonuclease-treated fraction II, indicating that RNA in the ribosomal vaccine might act as an adjuvant or a carrier in the presentation of the of the contaminating cell envelope antigens. The protective activity and the toxicity of fraction II were compared with the protective activity and the toxicity of fraction I, which contained cell envelope components, including LPS, and of purified LPS. The results indicated that protection by the ribosomal vaccine was associated with a slightly higher toxicity than was protection by fraction I, whereas purified LPS was the most toxic vaccine.

O-antigenic specificity of the protective supernatant factor from Salmonella typhimurium effective in S. typhimurium-infected mice

A supernatant factor (SF) prepared from cultures of Salmonella typhimurium protected naturally susceptible inbred mice against challenge with S. typhimurium subcutaneously injected (s.c.i.), but not against Salmonella enteritidis, suggesting tha the relevant specificity involved lipopolysaccharide. Further experiments were performed with two transductant strains of S. typhimurium. Strain SH6701 has O-antigen 4 from S. typhimurium and SH6703 had O-antigen 9 from S. enteritidis. Immunization with SF from SH6701 protected 95% BALB/c mice challenged with 100 LD50 S. typhimurium s.c.i., whereas SH6703 immunization had no effect on survival or mean survival time. SH 6703 SF gave some protection against homologous challenge. Antibody titres and delayed-type hypersensitivity reactions were also tested in immunized mice. The SF was, therefore, specific in that O-antigen 4 was necessary to protect mice against S. typhimurium challenge. Since we have previously demonstrated protein to be necessary for protection by SF, the active factor may be in the form of a protein-lipopolysaccharide complex.

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.

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.

Ribonuclease-sensitive ribosomal vaccine of Pseudomonas aeruginosa

In mice, active protection against Pseudomonas aeruginosa could be induced with two fractions derived from a crude preparation of ribosomes from P. aeruginosa. The two fractions were obtained by gel filtration chromatography of the crude ribosomal preparation on Sepharose CL-2B. In fraction I, less than 1% of the ribonucleic acid (RNA) applied to the column was recovered. Fraction II contained RNA and protein in a ratio of 1.94. The presence of ribosomes in this fraction was confirmed by analysis on a sucrose density gradient. The protection by fraction I was not affected by treatment with ribonuclease; in contrast, incubation of fraction II with ribonuclease completely abolished active protection. Fraction I contained lipopolysaccharide (LPS) as was indicated by the presence of 2-keto-3-deoxyoctonic acid. No LPS was found in fraction II. The adjuvant dimethyl dioctadecyl ammonium bromide enhanced the protection by fraction II; however, immunity by a low dose of fraction I was abolished by dimethyl dioctadecyl ammonium bromide. Protection by fractions I and II appeared to be restricted to the homologous serotype of P. aeruginosa. These results indicate that RNA is required for protection by fraction II. Active protection by fraction I is likely due to LPS.

Immunization of mice with Trypanosoma cruzi polyribosomes

Studies were carried out with a polyribosomal fraction isolated from Trypanosoma cruzi Y epimastigotes, with the intention to determine both its immunogenic activity and the degree of protection it could induce against experimental T. cruzi infection. This fraction was assayed in four groups of mice by using different schedules of vaccination and varying the dose, intervals, and route of administration. Seven days after the last dose, the animals were sacrificed for immunological studies or subjected to challenge with T. cruzi trypomastigotes. The results obtained in all schedules showed that our polyribosomal fraction only induced a weak antibody response, but was capable of evoking an expressive cellular response. It was also shown that this fraction has the capacity of inducing a high degree of protection against T. cruzi infection, as determined by the decrease of parasitemia and the prolonged survival time of immunized animals.

Artificial Salmonella vaccines: O-antigenic oligosaccharide-protein conjugates induce protection against infection with Salmonella typhimurium

Outbred mice were vaccinated with various artificial Salmonella vaccines and subsequently challenged intraperitoneally with graded doses of virulent Salmonella typhimurium. The Salmonella vaccines used were: (i) octasaccharide, obtained by hydrolysis of the O-antigenic polysaccharide chain of S. typhimurium strain SH 4809 with phage P22-associated endo-rhamnosidase and covalently linked to either diphtheria toxin or edestine; (ii) purified outer membrane proteins (porins) from S. typhimurium; and (iii) octasaccharide covalently linked to porins. All vaccines induced significant protection against experimental infection of mice with S. typhimurium. However, vaccination with the octasaccharide-porin conjugate resulted in better protection than that obtained by vaccination with octasaccharide or porin vaccines separately. Rabbit antibodies raised against the different vaccines were also passively administered intravenously to mice. Such mice were protected against challenge with virulent S. typhimurium by antibodies specific for the S. typhimurium O-antigen or for the porins. Thus, active immunization with more than one surface component of Salmonella bacteria improved the efficacy of the vaccine. The data from the passive immunization experiments also emphasized the role of humoral immunity for protection against S. typhimurium infection.