Specific immune response in the human respiratory tract following oral immunization with live typhoid vaccine

Live oral Salmonella enterica serovar Typhi vaccines Ty21a and CVD 909 induce opsonophagocytic functional antibodies in humans that cross-react with S. Paratyphi A and S. Paratyphi B

Live oral Salmonella enterica serovar Typhi vaccine Ty21a induces specific antibodies that cross-react against Salmonella enterica serovar Paratyphi A and Salmonella enterica serovar Paratyphi B, although their functional role in clearance remains unknown. We utilized an in vitro assay with THP-1 macrophages to compare the phagocytosis and survival of Salmonella opsonized with heat-inactivated human sera obtained before and after vaccination with Ty21a or a live oral S. Typhi vaccine, CVD 909. Opsonization with postvaccination sera predominantly increased the phagocytosis of S. Typhi relative to the corresponding prevaccination sera, and increases were also observed with S. Paratyphi A and S. Paratyphi B, albeit of lower magnitudes. Relative to prevaccination sera, opsonization with the postvaccination sera reduced the survival inside macrophages of S. Typhi but not of S. Paratyphi A or S. Paratyphi B. Higher anti-S. Typhi O antigen (lipopolysaccharide [LPS]) IgG, but not IgA, antibody titers correlated significantly with postvaccination increases in opsonophagocytosis. No differences were observed between immunization with four doses of Ty21a or one dose of CVD 909. Ty21a and CVD 909 induced cross-reactive functional antibodies, predominantly against S. Typhi. IgG anti-LPS antibodies may be important in phagocytic clearance of these organisms. Therefore, measurement of functional antibodies might be important in assessing the immunogenicity of a new generation of typhoid and paratyphoid A vaccines. (The CVD 909 study has been registered at ClinicalTrials.gov under registration no. NCT00326443.).

Characterisation of a live Salmonella vaccine stably expressing the Mycobacterium tuberculosis Ag85B-ESAT6 fusion protein

A recombinant Salmonella enterica serovar Typhimurium (S. Typhimurium) vaccine strain was constructed that stably expressed the Mycobacterium tuberculosis fusion antigen Ag85B–ESAT6 from the chromosome. Live oral vaccination of mice with the Salmonella/Ag85B–ESAT6 strain generated a potent anti-Ag85B–ESAT6 T_H1 response with high antibody titres with a IgG2a-bias and significant IFN-γ production lasting over a 120-day period. When mice primed with the Salmonella/Ag85B–ESAT6 vaccine were mucosally boosted with the Ag85B–ESAT6 antigen and adjuvant the IFN-γ responses increased markedly. To determine the protective efficacy of this vaccine strain, guinea pigs were immunised and followed for a 30-week period after aerosol challenge with M. tuberculosis. The heterologous prime-boost strategy of live Salmonella vaccine followed by a systemic boost of antigen and adjuvant reduced the levels of M. tuberculosis bacteria in the lungs and spleen to the same extent as BCG. Additionally, this vaccination regimen was observed to be statistically equivalent in terms of protection to immunisation with BCG. Thus, live oral priming with the recombinant Salmonella/Ag85B–ESAT6 and boosting with Ag85B–ESAT6 plus the adjuvant LTK63 represents an effective mucosal vaccination regimen.

The prostate-associated lymphoid tissue (PALT) is linked to the expression of homing chemokines CXCL13 and CCL21

BACKGROUND

The genitourinary tract is regarded as part of the mucosal immune system. However, the structural and functional aspects of the human prostate-associated lymphoid tissue (PALT) have never been extensively explored.

METHODS

This article describes our investigation of this issue by means of immunohistological, confocal, and ultrastructural examination of the normal human prostate.

RESULTS

PALT consists of two main components: (1) intraepithelial leukocytes, namely CD3(+)T cells with prevalent CD8(+) and CD45RA(-)CD45RO(+) phenotype, sometimes CD69(+), followed by CD94(+)NK, CD11c(+)DCs, some expressing CD86, DC-SIGN(+)DCs and a few B lymphocytes; (2) lymphoid aggregates, frequently below the epithelia, arranged in B cell follicles, endowed with a central ICAM-1(+)VCAM-1(+)CD21(+)FDCs network expressing BLC/CXCL13, and parafollicular T cell areas crossed by PNAd(+)HEV-like vessels showing SLC/CCL21 expression. Parafollicular areas were formed of prevalent CD4(+)T lymphocytes, both CD45RA(-) and CD45RO(+), and intermingled with CD11c(+)DCs. Germinal-center-containing follicles are few and their parafollicular areas are scantily infiltrated by Foxp3(+)CD69(-) highly suppressive regulatory T cells. Most lymphoid follicles lack a distinct germinal center and their parafollicular area harbor numerous Foxp3(+)CD69(-) cells.

CONCLUSIONS

Comparison with the tonsils shows that PALT displays immunomorphological features required for the onset of cellular and humoral immune responses, while its T regulatory cells appear to function as suppressor-regulators of T and B cell responses.

Intranasal immunization strategy to impede pilin-mediated binding of Pseudomonas aeruginosa to airway epithelial cells

Prevention of pulmonary Pseudomonas aeruginosa infections represents a critical unmet medical need for cystic fibrosis (CF) patients. We have examined the tenet that a mucosal immunization approach can reduce interactions of a piliated form of this opportunistic pathogen with respiratory epithelial cells. Vaccinations were performed using ntPEpilinPAK, a protein chimera composed of a nontoxic form of P. aeruginosa exotoxin A (ntPE), where the C-terminal loop amino acid sequence of the PAK strain pilin protein was inserted in place of the ntPE Ib domain. Intranasal (i.n.) immunization of BALB/c mice with ntPEpilinPAK generated both serum and saliva immune responses. A series of in vitro studies showed that diluted samples of saliva obtained from immunized mice reduced pilin-dependent P. aeruginosa binding to polarized human tracheal epithelial cells, protected human pulmonary epithelial cells from cytotoxic actions associated with bacterial challenge, and reduced exotoxin A toxicity. Overall, i.n. administration of ntPEpilinPAK induced mucosal and systemic immune responses that may be beneficial for blocking early stage adhesion and/or infection events of epithelial cell-P. aeruginosa interactions at oropharyngeal surfaces.

Upper Respiratory Tract Immunity

Most viral infections occur via mucosal surfaces like the respiratory, gastrointestinal, or genital epithelium. The mucosal immune system is an important component of the body's defense against such infections and consequently induction of mucosal, in addition to systemic immunity, might improve vaccine efficacy. Several orally administered vaccines, for example, against poliovirus and gastrointestinal bacterial infections, have been developed and are widely used. In contrast, to date most vaccines against respiratory pathogens are applied parenterally and thus do not induce significant mucosal immunity. For the development of effective mucosal vaccines a more profound understanding of the immune mechanisms operative at mucosal surfaces and of the interplay between different mucosal compartments is needed. Moreover, factors like the dose, form of application, and type of mucosal adjuvants are critical to the induction of effective mucosal immunity. This brief review will focus mainly on the nasal route and will summarize some recent findings concerning the function of the mucosal immune system of the upper respiratory tract. Furthermore, routes of cross-immunization between distinct mucosal compartments and how they might be relevant to vaccine development will be addressed. Finally, I will outline critical factors for the rational design of nasal vaccines and in this context highlight some recent preclinical and clinical developments in the field.

Distinct mechanisms for cross-protection of the upper versus lower respiratory tract through intestinal priming

A main feature of the common mucosal immune system is that lymphocytes primed in one mucosal inductive site may home to distant mucosal effector sites. However, the mechanisms responsible for such cross-protection remain elusive. To address these we have used a model of local mucosal infection of mice with reovirus. In immunocompetent mice local duodenal priming protected against subsequent respiratory challenge. In the upper respiratory tract this protection appeared to be mainly mediated by specific IgA- and IgG2a-producing B cells, whereas ex vivo active effector memory CTL were found in the lower respiratory tract. In accordance with these findings, clearance of reovirus from the lower respiratory tract, but not from the upper respiratory tract, of infected SCID mice upon transfer of gut-primed lymphocytes depended on the presence of T cells. Taken together this study reveals that intestinal priming leads to protection of both the upper and lower respiratory tracts, however through distinct mechanisms. We suggest that cross-protection in the common mucosal immune system is mediated by trafficking of B cells and effector memory CTL.

Mucosal and systemic immune responses in humans after primary and booster immunizations with orally administered invasive and noninvasive live attenuated bacteria

The mucosal and systemic immune responses after primary and booster immunizations with two attenuated live oral vaccine strains derived from a noninvasive (Vibrio cholerae) and an invasive (Salmonella typhi) enteric pathogen were comparatively evaluated. Vaccination with S. typhi Ty21a elicited antibody-secreting cell (ASC) responses specific for S. typhi O9, 12 lipopolysaccharide (LPS), as well as significant increases in levels of immunoglobulin G (IgG) and IgA antibodies to the same antigen in serum. A strong systemic CD4(+) T-helper type 1 cell-mediated immune (CMI) response was also induced. In contrast to results with Ty21a, no evidence of a CMI response was obtained after primary immunization with V. cholerae CVD 103-HgR in spite of the good immunogenicity of the vaccine. Volunteers who received a single dose of CVD 103-HgR primarily developed an IgM ASC response against whole vaccine cells and purified V. cholerae Inaba LPS, and seroconversion of serum vibriocidal antibodies occurred in four of five subjects. Serum IgG anti-cholera toxin antibody titers were of lower magnitude. For both live vaccines, the volunteers still presented significant local immunity 14 months after primary immunization, as revealed by the elevated baseline antibody titers at the time of the booster immunization and the lower ASC, serum IgG, and vibriocidal antibody responses after the booster immunization. These results suggest that local immunity may interfere with colonization of the gut by both vaccine strains at least up to 14 months after basis immunization. Interestingly, despite a low secondary ASC response, Ty21a was able to boost both humoral (anti-LPS systemic IgG and IgA) and CMI responses. Evidence of a CMI response was also observed for one of three volunteers given a cholera vaccine booster dose. The direct comparison of results with two attenuated live oral vaccine strains in human volunteers clearly showed that the capacity of the vaccine strain to colonize specific body compartments conditions the pattern of vaccine-induced immune responses.

Oral and rectal immunization of adult female volunteers with a recombinant attenuated Salmonella typhi vaccine strain

An attenuated strain of Salmonella typhi delta(cya) delta(crp-cdt) delta(asd) expressing a gene encoding a hepatitis B virus core-pre-S protein was tested in female adult volunteers for its ability to elicit a systemic and a mucosal immune response. Specifically, our purpose was to evaluate the potential of such a vaccine strain to induce specific secretory immunoglobulin A (sIgA) at genital and rectal surfaces. Oral and rectal routes of immunization were compared: oral immunization induced seroconversion against the bacterial lipopolysaccharide (LPS) in six out of seven volunteers, while after rectal immunization only one out of six volunteers seroconverted against LPS. To our disappointment, the latter volunteer was also the only one who seroconverted against the carried antigen (pre-S1), demonstrating the poor ability of this live vaccine to induce an immune response against the carried antigen. Anti-LPS sIgA was found in both the vaginal and cervical secretions of a volunteer who presented a strong seroconversion after oral immunization (16-fold increase in anti-LPS IgG). Smaller amounts of anti-LPS sIgA were found in the rectal secretions of one orally and one rectally immunized volunteer and in the saliva of three orally and one rectally immunized woman. Our data show for the first time that it is possible to induce specific sIgA in the genital and rectal tracts of women by using an S. typhi vaccine strain.

Intransal or intragastric immunization with proteosome-Shigella lipopolysaccharide vaccines protects against lethal pneumonia in a murine model of Shigella infection

Mice immunized intransally or intragastrically with proteosome vaccines containing either Shigella sonnei or S. flexneri 2a lipopolysaccharide were protected against lethal pneumonia caused by homologous organisms in an experimental murine intranasal challenge model of Shigella infection. Histopathological analysis demonstrated that immunization also protected against the progressive lesions resulting from invasion of the pulmonary mucosa by S. sonnei. These data show that mucosal proteosome-lipopolysaccharide vaccines can protect against lethal bacterial pneumonia and indicate that such vaccines are promising candidates for protection against intestinal shigellosis.

Serum C-reactive protein and immune responses in dogs inoculated with Bordetella bronchiseptica (phase I cells)

Eight Beagle dogs were inoculated intrabronchially with 5 x 10(9) live, avirulent cells of Bordetella bronchiseptica L-414 strain (phase I cells) (B. bronchiseptica) to investigate the serum levels of their C-reactive protein, the white blood cell counts, the antibody responses to B. bronchiseptica in the sera and tracheal secretions, and the effects of prednisolone given to four of the dogs on C-reactive protein (CRP), white blood cells (WBC) and immune responses. In two Beagle dogs inoculated intrabronchially with sterile physiological saline, the concentrations of CRP and the WBC counts did not increase. CRP was markedly increased one day after inoculation in the dogs inoculated with B. bronchiseptica to 385.0-720.0 micrograms/ml (mean 498 +/- 132 micrograms/ml) in the group given the B. bronchiseptica inoculation only, and to 372.0-649.0 micrograms/ml (mean 551 +/- 106 micrograms/ml) in the group treated with prednisolone following inoculation of B. bronchiseptica, as determined by an enzyme-linked immunosorbent assay (ELISA). The CRP levels were 23-95 times the pre-inoculation values, which indicated that prednisolone had no effect on the production of CRP. In the prednisolone-treated group, the WBC count increased and stayed at an increased level for approximately 12 days. An indirect fluorescent antibody test led to the detection of anti-B. bronchiseptica IgM and IgG antibodies in the sera from 5 days after B. bronchiseptica inoculation and S-IgA and IgG anti-B. bronchiseptica antibodies in the tracheal secretions on the day after the challenge exposure to B. bronchiseptica. The increase in CRP after challenge exposure to B. bronchiseptica was significantly (p < 0.05) smaller than that found after the first inoculation of B. bronchiseptica.

Immune response in the lungs following oral immunization with bacterial lysates of respiratory pathogens

We have investigated the local immune response of the BALB/c mouse respiratory tract after oral immunization with a bacterial lysate of seven common respiratory pathogens. After two immunization on five consecutive days, we examined the immunoglobulin (immunoglobulin G [IgG], IgM, and IgA) secretion rates of cells isolated from the lungs and compared them with those of spleen cells of orally immunized and nonimmunized animals by using a new test system based on time-resolved fluorescence. The procedure followed the principle of the classical ELISPOT test with nitrocellulose-bottomed microtiter plates, but europium (Eu3+)-linked streptavidin rather than enzyme-conjugated streptavidin was used, with the advantage of quantifying secreted immunoglobulins instead of detecting single antibody-secreting cells. Lymphocytes isolated from the lungs of treated animals revealed significant increases in total and antigen-specific IgA synthesis compared with the rates of the controls, whereas IgG and IgM production rates showed no remarkable differences. In addition, the sera of treated mice revealed higher antigen-specific IgA titers but not increased IgM and IgG levels. We conclude that priming the gut-associated lymphoid tissue with bacterial antigens of pneumotropic microorganisms can elicit an enhanced IgA response in a distant mucosal effector site, such as the respiratory tract, according to the concept of a common mucosa-associated immune system.

Use of the Vibrio cholerae irgA gene as a locus for insertion and expression of heterologous antigens in cholera vaccine strains

Vibrio cholerae may be a particularly effective organism for use in delivering heterologous antigens to stimulate a common mucosal immune response. A live attenuated vaccine strain of V. cholerae was constructed from the ctxA deletion mutant 0395-N1, containing the B subunit of Shiga-like toxin I under the transcriptional control of the iron-regulated irgA promoter. The B subunit of Shiga-like toxin I is identical to the B subunit of Shiga toxin (StxB). irgA encodes the major iron-regulated outer membrane protein of V. cholerae, which is a known virulence factor for this organism. Clones of the structural gene irgA from the classical V. cholerae strain 0395, with the gene for the Shiga-like toxin I B subunit inserted under the control of the irgA promoter, were used to introduce an internal deletion of irgA into the chromosome of 0395-N1 by in vivo marker exchange, using the suicide vector plasmid pCVD442. This plasmid contains the sacB gene from Bacillus subtilis, which allowed positive selection for loss of plasmid sequences on exposure to sucrose. The construction of vaccine strains was confirmed by Southern hybridization studies and outer membrane protein analysis. The expression of StxB in the vaccine strain VAC2 following growth in high- or low-iron conditions was shown to be tightly iron-regulated by Western blot analysis and by quantification of StxB using a sandwich enzyme-linked immunosorbent assay. The production of StxB by VAC2 under low-iron conditions was greater than that of the reference strain Shigella dysenteriae 60R.(ABSTRACT TRUNCATED AT 250 WORDS)

Active immunisation and resistance to experimental acute pneumococcal otitis media

The middle ear mucosal system and the humoral systemic immune factors are the two immunological systems whose involvement in the defence against acute otitis media (AOM) have been most intensively studied. However, their respective importance and their mutual influence is not clear. In the present study, a rat model for pneumococcal AOM was used to further elucidate the involvement of systemic immunity in protection against pneumococcal AOM. Six groups of male Sprague-Dawley rats were immunised with pneumococcal vaccine (PneumovaxRN) or live pneumococci (type 3) via one of three different routes: intraperitoneally, into the gastrointestinal tract (GIT) or into the right middle ear. A subsequent middle ear challenge (re-challenge in one group) with the same pneumococcal strain was performed after 4 days to 8 weeks in the different groups. Systemic immunity was found to be triggered, not only by systemic immunisation, but also by antigenic stimulation of the mucosa in the middle ear and in the GIT. In all groups but that immunised in the GIT, no new peak of specific IgG antibody response was demonstrated in serum after middle ear challenge/re-challenge. In contrast, half of the rats immunised in the GIT showed such a response not only after the inoculation into the GIT but also after a later performed middle ear challenge. Though a faster resolution of pus from the middle ear was observed in rats from all but one group, a significant reduction in the number of rats who developed AOM occurred exclusively among those rats that had previously manifested serological response to immunisation in the GIT.

Old microbes with new faces: molecular biology and the design of new vaccines

Rational approaches to the design of live attenuated bacterial and viral recombinant vaccine strains are leading to the manipulation of old vaccines and the generation of new ones. The two basic problems to be solved are attenuation of pathogenic strains, and the stable expression of foreign antigens.

Indirect measurement of intestinal immune responses to an orally administered attenuated bacterial vaccine

Intestinal fluid, saliva, circulating peripheral blood lymphocytes (PBL), and serum samples obtained from 81 human adult subjects who had been orally vaccinated with either Salmonella typhi Ty21a or one of its recombinant derivatives were examined to determine the value of indirect measurements of an antigen-specific intestinal-immunoglobulin A (IgA) response. Salivary IgA failed to provide consistent or correlative responses, and no evidence of a significant relationship was apparent with the intestinal-IgA responses. No significant correlation between the specific increase in responses in serum IgA and intestinal IgA was evident. While the magnitude of the serum IgG response significantly correlated with the intestinal-IgA response (P = 0.00064), it failed to detect 14.8% of the intestinal-IgA responses. The observation that 16.6% of the subjects had delayed serum IgA responses, with a peak occurring after day 23 compared with days 12 to 14, may have contributed to the inadequacy of the serum IgA response as a correlative indicator. The serum IgG responses in these subjects were also of a diminished magnitude. Specific IgA production by circulating PBL was found to be the most sensitive (92.6% response rate) and correlative (P = 0.00071) indicator of a specific intestinal-IgA immune response. However, its value in predicting protective efficacy is untried. These studies confirm that for the assessment of an enteric bacterial vaccine, determination of in vitro specific IgA production by circulating PBL may offer a single measurement of specific immunity which is as useful as serum and intestinal measurements combined.

Effect of parenteral immunization on the intestinal immune response to Salmonella typhi Ty21a

The effects of parenteral administration of a killed typhoid vaccine on the intestinal immune response to live orally administered Salmonella typhi Ty21a in human subjects was evaluated. Priming with parenteral vaccination neither enhanced nor suppressed the subsequent specific serum and intestinal immunoglobulin A (IgA) immune responses to a booster course of live oral vaccine. Neither a single oral dose of live vaccine nor a single dose of parenteral vaccine had any measurable booster effect on the observed primary intestinal IgA response to the live oral vaccine. Two booster doses of subcutaneously administered killed typhoid vaccine did result in a significant increase in the specific intestinal IgA antibody in those subjects primed with the oral live vaccine. This response was comparable in magnitude to the primary intestinal response. No evidence of this response could be found in serum IgA, although nonsignificant rises in serum IgG were evident. Previous parenteral priming had no effect on secondary immune responses to a live oral vaccine in humans. Serum immune responses were generally found to be of little value as indicators of local intestinal immunity. This study confirmed that parenteral vaccination was only able to induce an intestinal immune response following priming with live, orally administered organisms and that multiple parenteral booster doses were necessary to induce a measurable effect on intestinal immune responses.