Salmonella typhimurium infection in calves: delayed specific skin reactions directed against the O-antigenic polysaccharide chain

Development of acquired immunity to Salmonella

Salmonella enterica serovar Typhi (S. typhi) causes human typhoid fever, a serious and widespread disease in developing countries. Other Salmonella serovars are associated with food-borne infections. The recent emergence of multi-drug-resistant Salmonella strains highlights the need for better preventive measures, including vaccination. The available vaccines against Salmonella infection do not confer optimal protection. The design of new Salmonella vaccines must be based on the identification of suitable virulence genes and on knowledge of the immunological mechanisms of resistance to the disease. Control and clearance of a vaccine strain rely on the phagocyte oxidative burst, reactive nitrogen intermediates, inflammatory cytokines and CD4(+) TCR-alphabeta(+) T cells and are controlled by genes including NRAMP1 and MHC class II. Vaccine-induced resistance to reinfection requires the presence of Th1-type immunological memory and anti-Salmonella antibodies. The interaction between T and B cells is essential for the development of resistance following vaccination. The identification of immunodeficiencies that render individuals more susceptible to salmonellosis must be taken into consideration when designing and testing live attenuated Salmonella vaccines. An ideal live Salmonella vaccine should therefore be safe, regardless of the immunological status of the vaccinee, but still immunogenic.

Salmonella: immune responses and vaccines

Salmonella infections are a serious medical and veterinary problem world-wide and cause concern in the food industry. Vaccination is an effective tool for the prevention of Salmonella infections. Host resistance to Salmonella relies initially on the production of inflammatory cytokines leading to the infiltration of activated inflammatory cells in the tissues. Thereafter T- and B-cell dependent specific immunity develops allowing the clearance of Salmonella microorganisms from the tissues and the establishment of long-lasting acquired immunity to re-infection. The increased resistance that develops after primary infection/ vaccination requires T-cells cytokines such as IFNgamma TNFalpha and IL12 in addition to opsonising antibody. However for reasons that are not fully understood seroconversion and/or the presence of detectable T-cell memory do not always correlate with the development of acquired resistance to infection.Whole-cell killed vaccines and subunit vaccines are used in the prevention of Salmonella infection in animals and in humans with variable results. A number of early live Salmonella vaccines derived empirically by chemical or u.v. mutagenesis proved to be immunogenic and protective and are still in use despite the need for repeated parenteral administration. Recent progress in the knowledge of the genetics of Salmonella virulence and modern recombinant DNA technology offers the possibility to introduce multiple defined attenuating and irreversible mutations into the bacterial genome. This has recently allowed the development of Salmonella strains devoid of significant side effects but still capable of inducing solid immunity after single oral administration. Live attenuated Salmonella vaccines have been used for the expression of heterologous antigens/proteins that can be successfully delivered to the immune system. Furthermore Salmonella can transfer plasmids encoding foreign antigens under the control of eukaryotic promoters (DNA vaccines) to antigen-presenting cells resulting in targeted delivery of DNA vaccines to these cells. Despite the great recent advances in the development of Salmonella vaccines a large proportion of the work has been conducted in laboratory rodents and more research in other animal species is required.

Comparison between persisting anti-lipopolysaccharide antibodies and culture at postmortem in salmonella-infected cattle herds

Herds with recent clinical outbreaks of Salmonella dublin (7 herds) and S. typhimurium (4 herds) infections were followed serologically in O-antigen ELISAs over about one year, divided in four equal sampling phases. Animals found to be persistent high-reactors or seronegative at the end of the study were slaughtered and subsequently cultured for salmonella in a selected number of organ samples. Approximately 3% of all animals had high seroreactions up to 17 months after the outbreaks, and less than half of the seropositive animals in the S. dublin-infected herds were salmonella culture positive at slaughter (14/31). However, one persistently seronegative animal was also culture positive. Furthermore, as much as 70% of the male calves investigated at postmortem in the S. dublin-infected herds were high-reactors, among which approx. 56% were culture positive. Surprisingly, 2 of the 14 animals found culture positive turned out to be culture positive for S. typhimurium only. In the S. typhimurium study, none of the 17 animals investigated at postmortem were salmonella culture positive. All sera from these animals were negative in the O:9 blocking ELISA, and no serum sample was positive in the S. dublin ELISA, alone. In conclusion, although serology based on the O-antigens appears to be useful to identify salmonella-infected herds, it seems to be insufficient for identification of persistently infected animals.

The kinetoplastid membrane protein 11 of Leishmania donovani and African trypanosomes is a potent stimulator of T-lymphocyte proliferation

Kinetoplastid membrane protein 11 (KMP-11) from Leishmania donovani is an abundant 11-kDa surface membrane glycoprotein. Lymph node cells from mice of six different H-2 haplotypes immunized with KMP-11 or with L. donovani promastigotes were stimulated to proliferate in vitro KMP-11. Primed purified T cells required antigen presentation since they were not stimulated unless KMP-11-pulsed or L. donovani-infected macrophages were added. Promastigotes of a wide variety of Leishmania species and procyclic forms of African trypanosomes stimulated proliferation of KMP-11-primed or L. donovani promastigote-primed lymph node cells. All of the Leishmania promastigotes and African trypanosomes tested contained an 11-kDa protein, as detected by immunoblotting with KMP-11-specific monoclonal antibodies. The widespread distribution of the 11-kDa (KMP-11) molecules and their ability to stimulate strong T-lymphocyte proliferation in a non-H-restricted fashion suggest that they may be important molecules for induction of cell-mediated immune responses.

Mucosal immune responses in calves orally vaccinated with a live auxotrophic aroA Salmonella dublin strain

The mucosal immune responses were studied in two calves orally vaccinated with the live aroA mutant strain, Salmonella dublin SL5631, and in two non-vaccinated control calves. Intestinal secretions were collected through a permanent fistula in place during a 5-week period. Vaccinated calves responded with high IgM and IgA titres against the S. dublin lipopolysaccharide. Both IgA and the IgM titres appeared already after 3 days and IgM somewhat earlier than the IgA titres. Both antibody titres remained high for 2 weeks after the third and final vaccine dose. The calves also showed marked T-cell responses in lymphocytes collected from mesenterial lymph nodes and the spleen.

Immune response of pigs to parenteral vaccination with an aromatic-dependent mutant of Salmonella typhimurium

Cellular and humoral immune responses to parenteral vaccination with an aromatic-defined (aroA) Salmonella typhimurium and to oral challenge with the S. typhimurium parent strain were examined in pigs. The effectiveness of aroA S. typhimurium vaccination for prevention of clinical disease following challenge was also evaluated. A split litter model was utilized and analysis of variance was by least squares. The statistical model accounted for the effects of vaccination and litter. Parenteral vaccination of pigs with the aroA mutant induced a significant O-polysaccharide (O-ps) specific lymphocyte blastogenic response as well as a significant antibody response to O-ps, lipopolysaccharide and killed bacteria. The aroA strain was avirulent in pigs, was not shed in the feces and significantly reduced the severity of diarrhea following oral challenge.

Salmonella O antigen-specific oligosaccharide-octyl conjugates activate complement via the alternative pathway at different rates depending on the structure of the O antigen

Artificial Salmonella serogroup B, D or Cl-specific glycolipids were prepared by covalently linking oligosaccharides corresponding to two O-antigen repeating units, obtained by phage enzyme hydrolysis of native O-antigenic polysaccharides, to octyl residues. Sheep erythrocytes coated with the artificial glycolipids were studied for their ability to consume C3, when incubated in C4- deficient guinea pig serum. Salmonella C1 (0-6,7) glycolipid-coated erythrocytes consumed C3 40% more efficiently than Salmonella D (0-9,12) glycolipid-coated erythrocytes, and 10-times more efficiently than Salmonella B (0-4,12) glycolipid-coated erythrocytes. These results resemble C3 consumption by Salmonella C1, D, and B cells and by sheep erythrocytes coated with purified lipopolysaccharides of these O-specificities. The results prove directly that in a particulate system C3 activation via the alternative pathway depends on the structural properties of the O-antigenic side chain. Structures as small as octasaccharides, or as two O-antigenic repeating units, are sufficient for triggering C3 activation, but the magnitude of activation depends on the nature of the monosaccharides. Apparently, neither the core oligosaccharide nor Lipid A of lipopolysaccharide are required for C3 activation via the alternative pathway.

Evidence of T-cell recognition in mice of a purified lipophosphoglycan from Leishmania major

We have previously reported that a Leishmania major lipophosphoglycan (LPG), given with killed Corynebacterium parvum as an adjuvant, can vaccinate mice against cutaneous leishmaniasis. In order to analyze whether T cells are able to recognize this important parasite antigen, we have studied both humoral and cellular immune responses to L. major LPG that had been isolated from promastigotes by sequential solvent extraction and hydrophobic chromatography. The data show that immunization of mice with highly purified LPG induced an increase in frequency of L. major-reactive T cells and the production of immunoglobulin G antibodies to LPG. Furthermore, genetically resistant mice infected with L. major were able to develop a specific delayed-type hypersensitivity response in the ear to L. major LPG. These findings strongly suggest that T cells can recognize and respond to glycolipid antigens, in this case a host-protective Leishmania LPG, even though such antigens appear not to be potent T-cell stimulators in mice.

Oral Salmonella typhimurium vaccine expressing circumsporozoite protein protects against malaria

Immunization with radiation-attenuated malaria sporozoites induces potent cellular immune responses, but the target antigens are unknown and have not previously been elicited by subunit vaccines prepared from the circumsporozoite (CS) protein. A method is described here for inducing protective cell-mediated immunity to sporozoites by immunization with attenuated Salmonella typhimurium transformed with the Plasmodium berghei CS gene. These transformants constitutively express CS antigens and, when used to immunize mice orally, colonize the liver, induce antigen-specific cell-mediated immunity, and protect mice against sporozoite challenge in the absence of antisporozoite antibodies. These data indicate that the CS protein contains T cell epitopes capable of inducing protective cell-mediated immunity, and emphasize the importance of proper antigen presentation in generating this response. Analogous, orally administered vaccines against human malaria might be feasible.

The way ahead for vaccines and vaccination: symposium summary

In this summary, several biological and non-biological constraints to rapid progress in the molecular vaccine era are highlighted such as genetically-based unresponsiveness, induction of inappropriate immune responses, sustaining protective immunity in the vaccines problems in demonstrating efficacy, and ensuring availability and usage of this class of biologicals throughout the world. Some approaches to increasing immunogenicity are discussed with emphasis on composite antigens. Finally, the eight broad strategies for constructing vaccines outlined by Chanock in 1984 are re-examined.

Injection versus infection: The cellular immunology of parasitism

Parasites are immunogenic. But the variety of immune responses they can elicit is matched by their range of mechanisms to evade, subvert or distract these responses. The parasites' aim is survival and reproduction, ours is to restrict or eliminate them, and amplification of protective immune responses has become a key approach to this. But while vaccination has achieved many successes against the 'simpler' organisms such as viruses, the more complex protozoa and helminth parasites have proven much less tractable. In this article, Graham Mitchell discusses the differences between immune responses operated by whole parasites and those induced by prepared fractions.

An outer membrane protein (porin) as an eliciting antigen for delayed-type hypersensitivity in murine salmonellosis

The porin, an outer membrane protein of Salmonella typhimurium, was found to be a suitable antigen for eliciting delayed-type hypersensitivity in mouse salmonellosis. Histological examination of the reaction site revealed that the porin was superior to other antigenic preparations in eliciting a typical delayed-type hypersensitivity reaction consisting of mononuclear cell infiltration without polymorphonuclear cell contamination. This study indicates the importance of using a suitable protein antigen from S. typhi for human application.

Safety, infectivity, immunogenicity, and in vivo stability of two attenuated auxotrophic mutant strains of Salmonella typhi, 541Ty and 543Ty, as live oral vaccines in humans

Two Salmonella typhi mutants, 541Ty (Vi+) and 543Ty (Vi-), auxotrophic for p-aminobenzoate and adenine, were evaluated as live oral vaccines. 33 volunteers ingested single doses of 10(8), 10(9), or 10(10) vaccine organisms, while four others received two 2 X 10(9) organism doses 4 d apart. No adverse reactions were observed. Vaccine was recovered from coprocultures of 29 of 37 vaccinees (78%) and from duodenal string cultures of two; repeated blood cultures were negative. The humoral antibody response to S. typhi O, H, Vi, and lysate antigens in serum and intestinal fluid was meager. In contrast, all vaccinees manifested cell-mediated immune responses. After vaccination, 69% of vaccinees overall and 89% of recipients of doses greater than or equal to 10(9) responded to S. typhi particulate or purified O polysaccharide antigens in lymphocyte replication studies but not to antigens of other Salmonella or Escherichia coli. All individuals, postvaccination, demonstrated a significant plasma-dependent mononuclear cell inhibition of wild S. typhi.

Cellular and humoral immune response to a phenolic glycolipid antigen (PhenGL-I) in patients with leprosy

The ability of phenolic glycolipid I (PhenGL-I) of Mycobacterium leprae to stimulate in vitro lymphocyte proliferation (LP) was tested in cultures of peripheral blood cells from 42 patients with leprosy in Chicago and Thailand, 9 individuals with household contact in Thailand, and 10 unexposed North American controls. Only 10 responders (24%) were found among the patients, and the degree of LP was small. Responders were found among patients with lepromatous (18%) or tuberculoid (30%) leprosy without relation to age, complications, duration of treatment, or lepromin responsiveness. The specificity of the response was supported by a lack of response to two other glycolipids, by responses by T cells but not B cells, and by the observation that three of four responders tested maintained their responses to PhenGL-I for at least 1 year. Serum immunoglobulin M (IgM) and IgG antibodies were measured in the same patients by using PhenGL-I or its terminal monosaccharide conjugated to a bovine serum albumin carrier in an enzyme-linked immunosorbent assay. The presence of IgM antibody correlated negatively with LP to lepromin and to PhenGL-I in patients with tuberculoid leprosy. We conclude that circulating T cells from some leprosy patients proliferate in the presence of PhenGL-I in vitro, but the response is weak, possibly due to concomitant suppression or inhibition. The predominance of IgM antibody to PhenGL-I may be related to a lack of a T-helper-cell-mediated switch to IgG antibody response.

Immunization against experimental murine salmonellosis with liposome-associated O-antigen

Partially delipidated Salmonella typhimurium (O-1,4,5,12) lipopolysaccharide was incorporated into small multilamellar liposomes composed of either naturally occurring or synthetic phospholipids. Vaccination of mice with the liposome-lipopolysaccharide complexes induced a cellular response specific for O-1,4,5,12 determinants, as determined by the development of a delayed-type hypersensitivity reaction. The liposome-lipopolysaccharide vaccines were significantly more effective, compared with other nonviable vaccines tested, in protecting mice against a lethal intravenous challenge infection with virulent S. typhimurium. Protection afforded by the liposome-lipopolysaccharide vaccines was comparable to that conferred by a live S. typhimurium vaccine. Results suggest that liposome-induced modulation of the host immune response in favor of cell-mediated immunity may be more efficacious in preventing diseases in which cell-mediated immunity is of prime importance.

Blastogenic response of bovine lymphocytes to Brucella abortus lipopolysaccharide

Brucella abortus lipopolysaccharide was tested in a blastogenesis assay with unfractionated and nylon wool-separated peripheral blood lymphocytes of Brucella-naive cattle and cattle immunized with B. abortus. Our results indicated that in cattle the lipopolysaccharide of B. abortus is not a B-cell mitogen. In immunized animals it stimulated predominantly nylon wool-adherent cells. The lipopolysaccharide of Escherichia coli O128:B12, in contrast, induced a substantially greater proliferative response in circulating lymphocytes, predominantly those adherent to nylon wool, of the Brucella-naive cattle.

New knowledge on pathogenesis of bacterial enteric infections as applied to vaccine development

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Induction of endotoxin tolerance with nonpyrogenic O-antigenic oligosaccharide-protein conjugates

We prepared a dodecasaccharide, specific for the O-antigenic polysaccharide chain of Salmonella typhimurium (O-antigens 4 and 12), by the partial hydrolysis of the O-polysaccharide chain, utilizing bacteriophage 28B endo-alpha-L-rhamnosidase. The dodecasaccharide was shown by chemical and spectroscopical analyses to be totally devoid of lipid A and core oligosaccharide. By coupling this dodecasaccharide to human serum albumin, a glycoconjugate (DODECA-4809-ITC-HSA) was prepared and found to be (i) nonpyrogenic, (ii) unable to gelate a Limulus amoebocyte lysate, and (iii) unable to induce early-phase pyrogenic tolerance to endotoxin. Rabbits immunized either intravenously (with the glycoconjugate suspended in saline) or intrapopliteally (with the glycoconjugate suspended in Freund complete adjuvant) developed a significant although modest pyrogenic tolerance against challenge with the O-antigenic homologous S. typhimurium lipopolysaccharide (P less than 0.025 and P less than 0.01 for immunized and control rabbits, respectively). The evoked tolerance was O-antigen specific since no pyrogenic tolerance against challenge with lipopolysaccharide from S. thompson (possessing identical lipid A and core oligosaccharide structures but differing in the O-antigen polysaccharide chain) could be seen (P greater than 0.1). These results demonstrate that a nonpyrogenic O-antigenic polysaccharide hapten, when coupled to an immunogenic carrier protein, evokes immune responses which mediate significant, although modest, late-phase tolerance and is capable of partly reducing the pyrogenic activity of the O-antigenic homologous lipopolysaccharide.

Salmonella typhimurium infection in calves: protection and survival of virulent challenge bacteria after immunization with live or inactivated vaccines

Salmonella typhimurium SL1479, an auxotrophic mutant strain having a complete block in the aromatic biosynthetic pathway and therefore requiring p-aminobenzoic acid and 2,3-dihydroxybenzoate not available in mammalian tissues, was given orally in a dose of 10(10) live bacteria to 4- to 5-week-old calves. Only a mild transient fever response was seen. Strain SL1479 was unable to colonize and persist in the calves for more than 2 weeks. In a vaccination experiment, groups of six calves were (i) orally vaccinated with the live S. typhimurium SL1479 strain, (ii) subcutaneously vaccinated with a heat-inactivated S. typhimurium SVA1232 strain with aluminum hydroxide as adjuvant, or (iii) not vaccinated, to serve as controls. Calves were orally challenged with the live, calf-virulent S. typhimurium SVA44 strain: either 10(6) bacteria (equivalent to 100 25% lethal doses [LD25S]) or 10(9) bacteria (100,000 LD25S doses). The live oral vaccine gave significantly better protection than the heat-vaccinated, subcutaneously injected vaccine since (i) only control calves and calves given the killed vaccine developed profuse diarrhea, (ii) clinically, the mild fever responses seen after challenge in calves given the live vaccine were significantly lower (P less than 0.0005), (iii) autopsies performed 21 days after the challenge infection revealed normal findings in calves given the live vaccine, whereas calves given the killed vaccine showed signs of acute enteritis and chronic salmonellosis, (iv) all 12 calves given either 100 X or 100,000 X the LD25 survived the 21-day observation period; the mean survival time in nonvaccinated calves was 8.0 days; in calves given heat-inactivated vaccine and 100 X the LD25 it was 21.0 days, and in calves given 100,000 X the LD25 it was 11.5 days, (v) the fecal bacterial counts of the challenge S. typhimurium SVA44 strain were significantly lower (P less than 0.0005) in both groups given the live vaccine, and (vi) upon autopsy followed by culture, the qualitative recovery of the challenge strain from the alimentary canals and tissues of calves given the live vaccine was significantly lower (P less than 0.005).

Salmonella typhimurium infection in calves: cell-mediated and humoral immune reactions before and after challenge with live virulent bacteria in calves given live or inactivated vaccines

Groups of six calves, 4 to 5 weeks old, were vaccinated either orally with a live auxotrophic Salmonella typhimurium (O-antigen 1,4,12) SL1479 vaccine (10(8) bacteria on day zero, 10(10) bacteria on days 7 and 14) or subcutaneously with a heat-inactivated (56 degrees C, 30 min) S. typhimurium SVA1232 vaccine (10(10) bacteria suspended in 30% [vol/vol] aluminum hydroxide on days zero, 7, and 14). The calves were then orally challenged with either 10(6) (approximately 100 X the 25% lethal dose) or 10(9) (approximately 100,000 X the 25% lethal dose) live bacteria of the calf-virulent S. typhimurium SVA44 strain. The immune reactivity of these calves and of nonvaccinated control calves was followed before and after the challenge infection up to 42 days by (i) intradermal injection of S. typhimurium crude extract, outer membrane protein preparation (porins), and lipopolysaccharide (LPS), (ii) in vitro stimulation of peripheral blood lymphocytes estimated by using uptake of [3H]thymidine, with S. typhimurium crude extract, porins, LPS, and polysaccharide (O-antigenic polysaccharide chain free of lipid A), and Salmonella sp. serotype thompson (O-antigen 6,7) strain IS40 LPS and polysaccharide, and (iii) estimation of the class-specific immunoglobulin G (IgG) and IgM antibody responses against S. typhimurium LPS and porins, and Salmonella sp. serotype thompson LPS. The immune studies showed that in calves given the live vaccine orally, the skin test reactivity and lymphocyte stimulation indices were significantly higher (P values ranging from less than 0.025 to less than 0.0005) against homologous, but not heterologous, antigens than those seen in calves given the heat-inactivated vaccine subcutaneously. In contrast, the IgG and IgM antibody titers against homologous LPS and porins were significantly higher (P less than 0.0005) in sera collected on day 21 from calves given the heat-inactivated vaccine than in calves given the live vaccine. After the oral challenge, calves given the live vaccine showed reduced cell-mediated immune reactions, in agreement with the observation that the host defense could eradicate the challenge organism, whereas calves given the heat-inactivated vaccine showed significantly increased cell-mediated immune reactions (P values ranging from less than 0.025 to less than 0.005), in agreement with the observation that in these calves, the challenge strain caused enteritis as well as systemic invasion. The increased cell-mediated immune reactivity in calves given the live vaccine correlated well with the excellent protection against challenge infection seen in these animals.

Salmonella typhimurium infection in calves: specific immune reactivity against O-antigenic polysaccharide detectable in in vitro assays

Peripheral blood lymphocytes collected from calves infected experimentally with Salmonella typhimurium (O antigens 4,5,12) or Salmonella sp. serotype dublin (O 9,12) were stimulated with various bacterial cell envelope components, and their [3H]thymidine incorporation was measured. It was found that peripheral blood lymphocytes from infected calves incorporated significantly more [3H]thymidine than peripheral blood lymphocytes from uninfected controls (P values ranged from less than 0.05 to less than 0.0005). The responder cell type was found in a B-cell-depleted and T-cell-enriched population. The Salmonella infections elicited T-cell responses against at least two cell envelope components: (i) a specific response against the O-antigenic polysaccharide chain of the lipopolysaccharide (This was evident in that a polysaccharide from S. enteritidis [O 9,12] which shares a trisaccharide structure [O antigen 12 determinant] with S. typhimurium stimulated [3H]thymidine uptake, which, although lower than in the homologous system, was significantly higher than that seen after incubation with unrelated Salmonella sp serotype thompson polysaccharide.) and (ii) a response against outer membrane proteins (porins), which are present in both S. typhimurium and Salmonella sp. serotype dublin. The experiments with peripheral blood lymphocytes from Salmonella sp. serotype dublin-infected calves gave results in excellent agreement with those obtained in S. typhimurium-infected calves.