Adoptive transfer of gut mucosal antitoxin memory by isolated B cells 1 year after oral immunization with cholera toxin

A protocol was elaborated for the adoptive transfer of lymphocytes from mice which were orally immunized with cholera toxin (CT) to enable the study of long-term gut mucosal immunological memory at the single-cell level. Mesenteric lymph node (MLN) cells were transferred 1 year after priming immunizations, and recipient animals were challenged perorally on days 1 and 2 with CT before sacrifice on day 6 to 7 following transfer of cells. Strong antitoxin ELISPOT spot-forming cell (SFC) responses were recorded in spleens, MLN, and laminae propriae (LP) of recipient mice. In contrast, no SFC were found in Peyer's patches. The magnitude of the response equaled that of the acute response seen after optimal oral CT immunization and was directly dependent on the number of transferred cells. The memory antitoxin response in MLN and LP required oral challenge with CT as opposed to the spleen SFC response, which could also be triggered by intravenous challenge with antigen. Spleen cells from mice immunized perorally with CT were as effective as MLN cells in transferring immunological memory detectable in the gut immune system. Irrespective of the tissue source of transferring immunological memory detectable in the gut immune system. Irrespective of the tissue source of the memory cells, the isotype distribution of the antitoxin SFC response in recipient mice was similar with predominantly immunoglobulin A (96%) in LP and immunoglobulin G (66%) in MLN and spleen. Transfer of antitoxic memory was completely abrogated by treatment of the cells with J11d monoclonal antibody and complement prior to their injection into recipient mice by was unaffected by treatment with anti-Thy-1.2 antibody and complement, suggesting that long-term gut mucosal memory is carried by B cells. Antitoxin B memory cells might help explain the long-term protection against recurrent disease seen in convalescents from cholera in cholera-endemic areas.

The immunological consequences of feeding cholera toxin. II. Mechanisms responsible for the induction of oral tolerance for DTH

The mechanisms behind the induction of oral tolerance after feeding cholera toxin (CT) were examined using cell and serum transfer protocols. The feeding of CT or cholera toxoid (TD) induced a splenic cell capable of inhibiting the induction of systemic delayed-type hypersensitivity (DTH) but not humoral immunity. Depletion studies showed that this cell was Thy-1.2 positive. Transfer experiments suggested that suppressor cell activity was present in the mesenteric lymph nodes (MLN) and spleens of donor mice 1 week but not 3 days after feeding CT. When spleen cells were transferred to syngeneic recipients at various times after immunization, they were more effective at inhibiting systemic DTH when transferred within a short time of immunization. If the cells were transferred 6 days after immunization they no longer suppressed the development of DTH, which suggested that they inhibit the afferent limb of this immune response. This has been confirmed by the failure of a tolerogenic dose of CT, administered by gavage, to suppress the activity of mature effector TDTH cells. Serum collected 1 hr after feeding CT also suppressed the induction of systemic DTH. However, the tolerogenic activity of CT-fed serum was abrogated by the pretreatment of recipients with cyclophosphamide (Cy) (100 mg/kg), suggesting that this activity is mediated through the induction of suppressor cells. Transfer of fed serum, however, did not induce the splenic suppressor cell described above and we would suggest that several mechanisms may operate in the mucosal regulation of systemic DTH.

The immunological consequences of feeding cholera toxin. I. Feeding cholera toxin suppresses the induction of systemic delayed-type hypersensitivity but not humoral immunity

Immunization of adult BALB/c mice with 1 microgram cholera toxin (CT) in complete Freund's adjuvant (CFA) induced both humoral (IgG and IgA) and cell-mediated (DTH) immunity. Although an immunopurified, formalinized, cholera toxoid (TD) in CFA was inferior to the native holotoxin at inducing antitoxin antibodies, both cholera-derived antigens were equally immunogenic for specific DTH. When mice were fed either 1 microgram CT or 5 microgram TD 1 week before immunization, the induction of DTH was inhibited but the development of specific antibody was the same as in sham-fed controls. A feed of 10 micrograms CT not only suppressed the induction of DTH but also enhanced the IgG antitoxin responses measured 1 week after immunization. A dose of TD (50 micrograms), with a similar cholera toxin B subunit content, also induced oral tolerance for DTH but had no effect on the subsequent development of humoral immunity. The smallest doses of CT or TD fed (0.1 microgram and 0.5 microgram, respectively) failed to affect the development of either limb of the systemic immune response. These results suggest that oral tolerance for DTH is not consequent upon the metabolic actions of CT but that stimulation of systemic antibodies after enteric administration may be. Pretreating mice with cyclophosphamide (Cy) (100 mg/kg) before feeding CT abrogated the induction of oral tolerance for DTH but had no effect on humoral immunity, suggesting that suppressor T cells may be responsible for the induction of oral tolerance in these animals.

Oral immunization with a free peptide from cholera toxin: local protection and IgA production

It is frequently of great benefit for good protection against pathogens to elicit a local immunization. For example the importance of antibacterial as well as antitoxin local secretory IgA, for protection against cholera, has been underlined in several studies. We have already reported that oral administration of the peptide corresponding to the 50-75 sequence of cholera toxin (CT) B subunit elicits serum antibodies neutralizing CT activity. In this study we demonstrate that IgA with specificity to CT are present in intestinal secretions of mice immunized orally with the P50-75 or P30-50 peptides of CT B subunit. In addition local protection is observed in the intestine of P50-75 orally immunized mice. These results point out the potential of synthetic peptides as immunogens at the mucosal level.

Oral immunization with Sendai virus in mice

We have shown that in mice cholera toxin can be an effective adjuvant for gastrointestinal immune responses against a virus. The adjuvant properties can be increased and even dissociated from the toxic properties if virus and toxoid are covalently linked. Finally, oral immunization with these preparations of cholera toxin/toxoid and Sendai virus can be used to prime for respiratory immune responses to Sendai virus in which protection from infection correlates with IgA in the upper and with IgG in the lower respiratory tract.

Role of local IgA antitoxin-producing cells for intestinal protection against cholera toxin challenge

We examined in mice, perorally immunized with cholera toxin (CT) or cholera B subunit (CTB), the association between protection against intestinal toxin challenge and frequency and function of gut mucosal IgA antitoxin-forming cells. The in vitro production of IgA antitoxin by isolated cells and the toxin-neutralizing ability of culture supernatants were determined. Repeated oral immunizations with CT gave rise to high numbers of IgA antitoxin 'spot-forming' cells (SFC) in the lamina propria as well as to protection against challenge with CT in ligated intestinal loops. In contrast, mice immunized with purified CTB, gave poor IgA antitoxin SFC responses in the lamina propria and little or no protection. When a small amount of CT was used to adjuvant the response to CTB, many IgA antitoxin SFC were found; however, protection in intestinal loops remained poor. This discrepancy was explained by the predominant localization of antitoxin SFC in the proximal small intestine following oral CTB/CT-adjuvant immunization, whereas relatively few SFC were found further down in the intestine where the loop-protection test was performed. Thus, when lamina propria plasma cells were isolated from challenged loops and cultured in vitro, they released only low titers of IgA antitoxin and CT-neutralizing antibodies in culture supernatants; this was in contrast to cells from optimally immunized mice which gave supernatants with high IgA antitoxin and toxin-neutralizing antibody titers. Increasing the dose of CT, added as adjuvant to the CTB, resulted in better protection and higher numbers of IgA antitoxin SFC in more distal parts of the intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunogenicity of two formulations of oral cholera vaccine comprised of killed whole vibrios and the B subunit of cholera toxin

Two formulations of oral cholera vaccine were evaluated for safety and immunogenicity in adult volunteers in Thailand, an area with sporadic cholera outbreaks. One formulation consisted of 2 x 10(11) killed vibrios and 5 mg of cholera toxin B subunit, as was previously evaluated in North American volunteers, and the other consisted of 1 x 10(11) killed vibrios and 1 mg of B subunit, as was recently evaluated in a field trial in Bangladesh. Three doses of each formulation were given with citrate-bicarbonate buffer. Neither formulation had adverse effects. The formulations stimulated similar serum immunoglobulin G (IgG) and IgA responses to Vibrio cholerae lipopolysaccharide and cholera toxin and intestinal secretory IgA responses to lipopolysaccharide and toxin after three doses. The formulation containing twice the quantity of killed vibrios stimulated better vibriocidal responses, especially to Ogawa serotype. A formulation of oral vaccine containing more killed vibrios than were included in the vaccine studied in the Bangladesh field trial may provide greater protection against cholera.

Cholera toxin and its subunits as potential oral adjuvants

Cholera toxin has been shown to have adjuvant effects in multiple different systems. The dose, timing and genetic background of the recipient all seem to be important variables. The role of the two subunits in both the immunogenicity and the adjuvanticity of this molecule remain unclear. The mechanisms of the adjuvant effect likely involves effects on regulatory T cells; there is evidence that the adjuvant effect is due at least in part to inhibition of suppressor T cells. When KLH is used as a model antigen, the adjuvanticity of cholera toxin appears to be related to its immunogenicity in that both properties occur mainly in mouse strains that are high responders to cholera toxin. The genetic engineering of chimeric neoantigens consisting of cholera toxin subunits coupled to antigens of interest has been shown to be technically possible and is an attractive future approach for the generation of effective oral vaccines.

Cellular basis of immunomodulation by cholera toxin in vitro with possible association to the adjuvant function in vivo

Cholera toxin (CT) is a potent oral immunogen that also acts as a strong mucosal adjuvant for immune responses to related as well as unrelated Ag. To elucidate the immunomodulating effects of CT at the cellular level we have examined interactions of CT with APC and with B and T lymphocytes in vitro. CT markedly stimulated the production of IL-1 from APC (mouse peritoneal macrophages or macrophage cell line P388D1) but did not induce Ia-Ag and had marginal, if any, effect in potentiating Ia Ag expression stimulated by rIFN-gamma on these cells. CT had differential effect on T cell proliferation in vitro, usually strongly inhibitory but on Con A-stimulated spleen cells during prolonged (greater than or equal to 5 days) culture or when added on day 4 or later to these cultures up to a two- to three-fold enhancement of proliferation was seen. CT-induced inhibition of T cell proliferation was associated with decreased production of IL-2 and anergy to exogenously added IL-2 despite apparently normal expression of IL-2R. Similar to what was found with T cells LPS-stimulated spleen B cells demonstrated both inhibition and enhancement of proliferation in the presence of CT: in high concentrations (greater than or equal to 10(-8) M) and early in culture (day 3) CT had a strong inhibitory effect on the proliferation of B cells, whereas later (day 6) and/or at lower CT concentrations (10(-9) to 10(-11) M) the proliferation was increased up to 10-fold. The net effect of CT treatment on Ig-production by LPS-stimulated spleen B cells was seen as an enhanced level of IgA and IgG but not IgM in culture supernatants. The differential effects of CT on the cells of the immune system observed in vitro may, singly or in combination, explain the immunostimulatory function of CT.

The effect of opiates on the intestinal immune response to cholera toxin in mice

We studied the effect of opiates on the intestinal immunoglobulin A response in mice. C57BL mice were orally immunized by two doses of 10 micrograms of cholera toxin, 2 weeks apart. Experimental groups received subcutaneous injections of morphine, either 10 or 20 mg/kg/day, in two divided doses. Morphine was given for 4 days, starting 1 day prior to each cholera toxin dose. Intestinal secretions were collected by lavage 1 week after the last cholera toxin dose, and assayed for specific anticholera toxin antibody and total immunoglobulin A. Results were expressed as units of anticholera toxin per nanogram immunoglobulin A. It was found that morphine, 20 mg/kg/day, reduced the response from 30.9 +/- 3.11 to 9.78 +2- 1.42 units/ng (M +/- SEM; p less than 0.0001). 10 mg/kg/day of morphine slightly reduced the immune response to 21.38 +/- 3.51 units/ng (M +/- SEM), but failed to achieve statistical significance. Naloxone administration prior to morphine injections abolished the inhibitory effects of morphine. Morphine administration had no effect on the response to a booster dose of cholera toxin 3 months after the initial cholera toxin immunization and morphine administration. It is concluded that morphine has a significant inhibitory effect on the intestinal immune response, but does not effect long-term mucosal immunological memory. The effect is probably mediated by a specific opiate receptor, as it is blocked by naloxone. This effect may have clinical implications.

[Use of gnotobiotic animals for the study of the pathogenesis of cholera intoxication]

Germ-free suckling rabbits and minipigs can be recommended as models suitable for the study of different aspects of the pathogenesis of cholera intoxication. In minipigs, individual representatives of intestinal autochthonous microflora produce different effect on the sensitivity of the animals to the toxigenic and choleragenic action of Vibrio cholerae antigen introduced by oral administration, that should also be taken into consideration in the determination of residual toxicity during the trial of new vaccine preparations against cholera.

Effects of cholera toxin on delayed-type hypersensitivity to sheep red blood cells inoculated intranasally into mice

The effects of cholera toxin (CT) on delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC) were studied in mice sensitized by intranasal administration of SRBC. CT (1 microgram/mouse), given intranasally together with SRBC (2 x 10(7)/mouse), induced a maximally enhanced DTH response, which reached its peak around 7 days after sensitization, and also induced an accelerated DTH response upon a second administration of SRBC 28 days later. The ability of CT to enhance the DTH to SRBC was lost, either when CT was administered via the intraperitoneal or subcutaneous route, or when CT was introduced into the nasal site from which a large proportion of the SRBC was discharged 2 days after SRBC administration. These results indicate that the cells that are located in the nasal site and participate in the earlier events of DTH response were most affected by CT. The following effects of CT on the earlier events, which occur within 24 hr after the intranasal administration of both CT and SRBC, appeared to be involved in the mechanisms by which CT enhances DTH to SRBC: (i) facilitation of the penetration of the antigen into the nasal tissue; (ii) reinforcement of the migration of immunocompetent cells from the blood to the nasal tissues; (iii) promotion of the ability of Ia-positive macrophages to present the antigenic determinants to T cells; (iv) facilitation of the differentiation of primed T cells to DTH-effector T cells.

Protection against influenza virus infection by vaccine inoculated intranasally with cholera toxin B subunit

Secretory IgA antibodies in mucosa are known to play an essential role in protection against various infectious agents. To enhance the induction of protective mucosal antibodies, influenza HA vaccine was inoculated intranasally into mice with the B subunit of cholera toxin (CTB), which is known to be an excellent mucosal self-adjuvanting molecule. This combination resulted in high levels of antiviral IgA antibodies in nasal secretions and enhanced serum haemagglutinin-inhibiting (HI) antibodies 4 weeks after inoculation, compared with the inoculation of vaccine alone which induced only a low level of HI serum antibodies and no local IgA antibodies. (Subcutaneous or intraperitoneal inoculation of the vaccine with CTB failed to induce detectable nasal antiviral IgA antibodies). Levels of nasal IgA and serum HI antibodies increased in a dose-dependent fashion with increasing nasal doses of both vaccine and CTB, and correlated with the degree of protection against viral challenge. A greater protective effect was seen with cholera toxin than with its B subunit. Moreover, a second administration of vaccine alone, 4 weeks after the inoculation of the vaccine with CTB, elevated the level of the antiviral IgA nasal antibodies to 10-100 times higher than that of the primary response. These results suggest that either CT or CTB could be used as a potent adjuvant to induce protective secretory antibodies by nasal vaccination against pathogens impinging on respiratory mucosa.

Oral administration of cholera toxin-Sendai virus conjugate potentiates gut and respiratory immunity against Sendai virus

Successful oral immunization to prevent infectious diseases in the gastrointestinal tract as well as distant mucosal tissues may depend on the effectiveness of an Ag to induce gut immune responses. We and others have previously reported that cholera toxin possesses strong adjuvant effects on the gut immune response to co-administered Ag. To explore further adjuvant effects of cholera toxin, the holotoxin or its B subunit was chemically cross-linked to Sendai virus. The resulting conjugates, which were not infectious, were evaluated for their capacity to induce gut immune responses against Sendai virus after oral administration to mice. Conjugating cholera toxin to virus significantly enhanced the adjuvant activity of cholera toxin compared to simple mixing. Cholera toxin B subunit, however, did not show an adjuvant effect either by itself or conjugated with the virus. Oral administration of the Sendai virus-cholera toxin conjugate was also able to prime for protective anti-viral responses in the respiratory tract. Mice that were orally immunized with the conjugate and intra-nasally boosted with inactivated virus alone showed virus-specific IgA titers in nasal secretions that correlated with protection against direct nasal challenge with live Sendai virus. For comparison, s.c. immunization was also studied. Systemic immunization with the virus-cholera toxin conjugate induced virus-specific antibody responses in serum as well as in the respiratory tract but failed to protect the upper respiratory tract against virus challenge. Systemic immunization plus an intra-nasal boost did, however, confer a variable degree of protection to the upper respiratory tract, which correlated primarily with bronchoalveolar lavage (lung) antibody titers.

Field trial of oral cholera vaccines in Bangladesh: results of one year of follow-up

We assessed the protective efficacy (PE) of three doses of B subunit-killed whole cell (BS-WC) and killed whole cell-only (WC) oral cholera vaccines in a randomized, double-blind trial among 62,285 children and women residing in rural Bangladesh. After one complete year of surveillance, 110 cases of cholera were detected in the placebo group, 52 in the WC group (PE, 53%; P less than .0001), and 41 in the BS-WC group (PE, 62%; P less than .0001). Protection was greater for BS-WC recipients than for WC recipients only during the initial eight months of observation. Both vaccines conferred equivalent protection against cholera associated with life-threatening dehydration and against less severe cholera. High-grade, sustained protection was observed in persons vaccinated when older than five years; in younger persons protection was transient. We conclude that BS-WC and WC vaccines confer significant protection against cholera, particularly in persons vaccinated when older than five years.

The effect of splanchnic nerve stimulation and neuropeptide Y on cholera secretion and release of vasoactive intestinal polypeptide in the feline small intestine

The effect of sympathetic nerve stimulation and intra-arterial infusion of neuropeptide Y (NPY) on net fluid secretion and release of vasoactive intestinal polypeptide (VIP) was studied in the cat small intestine during a secretion due to cholera toxin. Activation of the splanchnic nerves (4 Hz, 5 ms, 5 V) decreased net fluid secretion to 57 +/- 10% of control. Concomitantly, the release of VIP was reduced to less than 50%. Furthermore, close i.a. infusion of NPY (estimated increase in plasma concentration 75 nmol l-1) reduced the net fluid secretion and VIP release to 27 +/- 5 and 28 +/- 4% of the pre-stimulatory value. The correlation between the decrease in net fluid secretion and reduction in VIP release showed a strong positive correlation (r = 0.83). These results strongly indicate that the antisecretory effect of sympathetic nerve stimulation during cholera diarrhoea is mediated by inhibition of secretory VIP neurons in the intestinal mucosa. A similar mechanism is also proposed for the intravascularly administered NPY.

[The role of the liver in the intestinal immune system. Origin of specific B-lymphocytes in the liver following intestinal immunization]

After intestinal priming with cholera toxin (CT) the highest number of specific B-cells is found in the liver, whereas after an intestinal booster dose of CT, high numbers of specific B-cells also locate to the intestine. Correspondingly, after priming, 70% of biliary IgA anti-CT are synthesized within the liver and after boosting approximately 30%. To test the hypothesis that the B-cells in the liver are derived from intestinal lymphoid tissue, thoracic duct lymphocytes (TDL) from intestinally primed and boosted donor rats were transferred to syngeneic recipients. TDL from primed donors predominantly homed to the liver of recipients, and TDL from boosted donors in high numbers to the intestine also. High biliary IgA anti-CT titers in both groups of recipients proved that the immune response was transmitted successfully. In the rat, at any rate, the liver is part of the intestinal immune system not only in terms of IgA transport but also as a specific homing organ for intestinal B-cells.

Cholera toxin neutralization: a comparison of purified serum IgG and biliary secretory IgA antibodies

Rats were immunized three times with cholera toxin via the intraintestinal or intravenous route, and their respective biliary secretory IgA (sIgA) or serum IgG antibodies were affinity-purified on a cholera toxin immunoabsorbent. On a molar basis, the sIgA antibodies were roughly seven-fold more efficient than IgG antibodies in neutralizing cholera toxin in the ligated intestinal loop assay. Various explanations for this difference in neutralizing capacity are proposed.

Combined oral/nasal immunization protects mice from Sendai virus infection

Based on the concept of a common mucosal immune system wherein mucosal associated lymphocytes traffic among the various mucous membranes, the murine gastrointestinal tract was immunized with Sendai virus antigens in order to elicit a virus-specific immune response in the respiratory tract. Multiple intragastric (oral) administration of live or killed Sendai virus induced IgA and IgG antiviral antibodies in both gastrointestinal secretions and serum. When cholera toxin as an adjuvant was included along with virus, gut IgA and IgG as well as serum IgA responses were enhanced. Antiviral antibodies induced in respiratory secretions by oral killed virus plus cholera toxin, however, were variable and protection from virus challenge was not demonstrated. Significantly higher levels of respiratory antiviral antibodies were induced if immunization with oral killed Sendai virus/cholera toxin was combined with intranasal administration of small amounts of killed virus. The combined immunization also resulted in protection of both the upper and lower respiratory tracts from virus infection. Protection of the upper respiratory tract was correlated with the presence of IgA antiviral antibodies in nasal washings. On the other hand, protection of the lower respiratory tract was correlated with IgG antiviral antibodies in bronchoalveolar lavage fluids. Immunization with intranasal killed virus alone conferred partial protection to the lower respiratory tract and no protection to the upper respiratory tract. Thus, oral immunization with killed virus antigen could prime for a protective immune response in the murine respiratory tract and this protective response included IgA antibodies.

Blood-cerebrospinal fluid barrier alteration following intraventricularly administered cholera toxin

Cholera toxin (CT) has been reported to double cerebrospinal fluid (CSF) formation following its introduction into the ventricular system of cats and dogs. In our laboratory we noted that CT used in a similar fashion in rabbits and cats resulted in only a slight increase in CSF formation and was associated with a steadily rising protein content in the cisterna magna effluent. To further investigate this finding, rabbits and cats underwent ventriculo-cisternal perfusions, one group with CT introduced into the ventricles and the other without. In the rabbit only, radioiodinated serum albumin (125I-RISA) was given i.v. Other groups of rabbits had 125I-RISA or 125I-CT injected into the ventricles. The group of rabbits receiving intraventricular CT experienced a 4-10-fold elevation in the amount of both protein and 125I-RISA in the cisterna magna effluent compared with the control group. Electrophoretic pattern of the protein present in the effluent was similar to that of rabbit plasma. Autoradiography of the brains of those animals given intraventricular 125I-CT were found to have a very high uptake of 125I-CT in the choroid plexus and along all exposed ventricular surfaces, a finding not evident when 125I-RISA alone was given intraventricularly. It is concluded that CT altered the blood-CSF barriers allowing the reference marker to penetrate these barriers and plasma to leak into the CSF. These findings appear to account for most if not all of what was thought to be an increase in CSF formation in response to intraventricular CT.

Specific antibody synthesis and biliary secretion by the rat liver after intestinal immunization with cholera toxin

This study was designed to investigate the location, specificity, and significance of antibody-containing cells in the liver. After intestinal administration of cholera toxin, high numbers of specific antibody-containing cells appeared in the liver during the early priming period and after boosting. In contrast, a significant number of specific antibody-containing cells appeared in the lamina propria of the intestine only after boosting. In the liver, the specific antibody-containing cells were predominantly located in the sinusoidal region of zone 1 of the liver lobules. About 80% of the specific antibody-producing cells in the liver synthesized anticholera toxin antibody of the immunoglobulin A class. During the priming period, the concentration of immunoglobulin A anticholera toxin in bile paralleled the increase and decrease in the number of specific antibody-containing cells in the liver. Liver perfusion experiments indicated that during the priming period at least 70% of the biliary immunoglobulin A anticholera toxin antibody was synthesized within the liver, whereas 30% was synthesized in the liver after boosting. Thus, during the early immune response, the liver seems to be the major source for specific biliary antibody to intestinally administered cholera toxin.

Efficacy of oral rehydration solutions in a rat model of secretory diarrhea

Controversy continues regarding the ideal composition of glucose/electrolyte solutions used for oral rehydration of infants and children with acute diarrhea. We have used cholera toxin-treated rat small intestine as a model of secretory diarrhea to assess the efficacy of oral rehydration solutions by intestinal perfusion. All solutions tested reversed net water secretion but a hypotonic bicarbonate-free solution was more effective than other solutions, including the World Health Organization oral rehydration solution (p less than 0.003). Net sodium secretion persisted with all solutions tested but there was a significant linear relationship between sodium concentration of the solution perfused and net sodium transport (r = 0.75, p less than 0.05). Cholera toxin treatment alone and in combination with perfusion of oral rehydration solutions significantly reduced plasma sodium concentration and osmolality (p less than 0.05), the effects being most marked with low sodium solutions. Although direct parallelism between observations in this animal model of secretory diarrhea and human diarrheal disease has not been established as yet, the model may be useful in assessing clinical efficacy of new oral rehydration solutions and in systematic analysis of the relative benefits of their individual components.

Protective efficacy in humans of killed whole-vibrio oral cholera vaccine with and without the B subunit of cholera toxin

Natural protection from cholera is associated with local intestinal antibacterial and antitoxic antibodies, which appear to act synergistically. Although current parenteral cholera vaccines offer insufficient protection, new vaccines administered orally have more promise. Killed Vibrio cholerae, alone or given with the B subunit of cholera toxin, was evaluated in adult volunteers. Vaccinees, who received three doses of either vaccine, and unvaccinated controls ingested 10(6) V. cholerae organisms to determine the protective efficacy of the vaccines. The combination vaccine provided 64% protection, and the whole vibrio vaccine given alone provided 56% protection. In addition, illnesses in vaccines were milder than those in controls, and both vaccines gave complete protection against more severe disease. This substantial level of protection against a dose of V. cholerae that caused cholera in nearly 90% of controls suggests that these vaccines might provide at least as high a level of protection if given to the population of an endemic area. Indeed, a field efficacy trial is underway in Bangladesh, and preliminary data indicate a protective efficacy of 85% for a killed whole vibrio plus B subunit vaccine similar to that tested in volunteers and an efficacy of 58% for the killed whole vibrio vaccine alone. Thus, the studies in human volunteers were successful in predicting the substantial protection afforded by the vaccines in a cholera endemic area.

B subunit-whole cell and whole cell-only oral vaccines against cholera: studies on reactogenicity and immunogenicity

We conducted a randomized trial among persons in rural Bangladesh to evaluate the side effects and immunogenicity of orally administered B subunit-killed whole cell (BS-WC) and killed whole cell-only (WC) cholera vaccines and a killed Escherichia coli strain K12 placebo proposed for field testing. Three doses of BS-WC, WC, E. coli, or a control agent were given with antacid to 1,257 women (aged greater than 15 years) and children (aged to to 15 years). The four groups exhibited no statistically significant differences in occurrence of symptoms after each dose, and rises in titers of vibriocidal (VC) antibodies to Inaba and Ogawa were twofold higher for vaccinees than for controls (P less than .001). Half of the persons with fourfold or greater VC responses to WC responded after the first dose; many additional patients, particularly young children, responded after subsequent doses. In contrast, 89% of persons who responded to BS-WC with twofold or greater rises in titer of IgG antibodies to cholera toxin did so after the first dose. After the third dose, vaccinees exhibited a fivefold higher rise in titer than did controls (P less than .001); a dose-to-dose booster effect was most evident in young children.

[Effect of intestinal microflora on the pathogenesis of cholera intoxication]

Germ-free minipigs, previously treated with bacteroids, develop cholinergic reaction after the intragastric administration of Vibrio cholerae exotoxin. The intensity of this reaction, disturbances in homeostasis, and the character of morphological changes depend on the dose of choleragen, the bacteroid strain, and the presence of the concomitant (Escherichia coli) and residual microflora in the intestine.

Effectiveness of liposomes as potential carriers of vaccines: applications to cholera toxin and human malaria sporozoite antigen

Two antigens, cholera toxin (CT) and a synthetic albumin-conjugated 16-residue peptide derived from the circumsporozoite (CS) protein of Plasmodium falciparum sporozoites, were tested as immunogens in rabbits. The malaria peptide-albumin conjugate by itself was completely nonimmunogenic, and although cholera toxin was immunogenic it also expressed considerable native toxicity. After attachment of CT to liposomes containing ganglioside GM1, toxicity of CT was completely eliminated and antigenicity was enhanced. Therefore liposomes may be capable of reducing toxicity of certain potentially dangerous antigens such as toxins. After incorporation of the malaria peptide-albumin conjugate into liposomes a high titre of specific antibodies was induced against the malaria peptide but not against albumin. These antibodies also reacted with native CS protein. Three adjuvants, including lipid A and two types of lipophilic muramyl dipeptide, were compared and found to be effective in liposomes. Based on the conversion of synthetic P. falciparum CS peptide from a nonimmunogenic to an immunogenic form and on the 'toxoiding' effect of liposomes for CT, it is concluded that liposomes should be considered as being a useful carrier for antigens and adjuvants for vaccines for poorly antigenic or toxic substances.

Protection of rats against cholera toxin and cholera-like enterotoxins by immunization with enteric-coated cholera toxin

Pure cholera toxin (CT) given as a booster in enteric-coated tablets to rats produced a humoral and intestinal immune response similar to the result of instilling the boosting dose of CT directly into the duodenum. This method protects the antigen against gastric acid and allows delivery of the immunogen to intestinal mucosa, an essential step in producing intestinal secretory IgA. Immunization gave protection against pure CT during intestinal perfusion but also significantly protected against the secretory effects of E. coli LT and CT-like toxin of A. sobria. The use of enteric-coated vaccines offers advantages for mass immunization programmes and our results suggest that immunization with preparations containing CT holotoxin may protect against heterologous toxins which cross-react with CT.

Intestinal mucosal memory and presence of memory cells in lamina propria and Peyer's patches in mice 2 years after oral immunization with cholera toxin

The build-up of long-term immunological memory in the gut mucosal immune system may explain long-lasting protection against new attacks of cholera in convalescents from natural disease. We have looked for gut mucosal antitoxin immunological memory and memory cells in mice after oral immunization with cholera toxin. Our results show that mice that were orally primed with cholera toxin and then boosted 2 years later with a single oral antigen dose mounted a rapid and vigorous IgA antitoxin response in the intestinal lamina propria. A specific secondary antitoxin response could also be elicited without any in-vivo boosting by in-vitro stimulation of isolated lymphocytes from the lamina propria, Peyer's patches, mesenteric lymph nodes, and spleen. The results provide evidence for the almost life-long persistence of anti-cholera toxin memory B cells (and perhaps also T cells) in the intestine and probably also recirculating cells, after oral immunization with cholera toxin. A functional antitoxic immune response may be boosted rapidly on renewed enteral exposure to cholera toxin by the stimulation of memory cells both in the lamina propria and in the Peyer's patches.

Cholera antibody production in vitro by peripheral blood lymphocytes following oral immunization of humans and mice

We have studied specific antibody production from peripheral blood lymphocytes (PBL) after oral cholera immunization of humans and mice. Two oral immunizations with cholera toxin (CT) in mice or a single dose of the combined cholera B-subunit/whole cell vaccine in humans gave rise to PBL which spontaneously secreted cholera-specific antibodies when cultured in vitro. A high proportion of IgA antibodies was seen in contrast to antibodies produced by PBL after parenteral immunization which were predominantly IgG. Cultured PBL produced antitoxin as well as anti-lipopolysaccharide antibodies after oral immunization, whereas serum only revealed titre rises for anti-CT. Antibody-secreting PBL appeared in the blood 2-4 days after immunization and persisted for about two weeks with a peak after 6-8 days. Mitogen stimulation in vitro of PBL from multiply-orally vaccinated humans activated a population of specific IgM antibody-secreting cells which persisted for several months following immunization, suggesting the presence of long-lived memory cells. The analysis of IgA antibody production from in-vitro cultured PBL seems to be a promising technique to assess the local immunogenicity of oral vaccines.

Appearance of dark keratinocytes following intracutaneous injection of cholera toxin in mouse skin

Intracutaneous injection of cholera toxin (CT), exotoxin of Vibrio cholerae, induces epidermal hyperplasia in mice, rats, and hamsters. In the work reported here we found that, like other hyperplasiogenic compounds such as 12-O-tetradecanoylphorbol-13-acetate which are tumor promoters, CT induces dark basal keratinocytes (dark cells) in the epidermis of mice. These are distinct from other epidermal cells since they contain dense cytoplasm rich in ribosomes and tonofilaments. This was demonstrated by electron microscopy and by toluidine blue staining of paraffin- or Epon-embedded sections. They comprised 3.1% of interfollicular basal cells 24-64 h after injection of 1 ng CT as compared with 0.5% in saline-injected skin. It was found by autoradiography of paraffin sections that about 47.2% of dark cells were labeled with [3H]thymidine at these times, while under the same conditions, labeling indices of basal cells were about 30% at the peaks. These results are discussed in relation to tumor promotion in two-stage carcinogenesis of mouse skin.

Inflammatory mechanisms in corneal ulceration

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Cholera toxin feeding did not induce oral tolerance in mice and abrogated oral tolerance to an unrelated protein antigen

The feeding of protein antigens to mice results in a state of tolerance when feeding is followed by parenteral immunization. Cholera toxin (CT) is a protein that has been used extensively as a potent oral immunogen for mucosal IgA responses, but CT feeding also stimulates a substantial plasma IgG antibody response. This latter finding prompted us to study whether or not CT induces oral tolerance. Mice were fed 5 mg keyhole limpet hemocyanin (KLH) or 10 micrograms CT at least twice before parenteral immunization with 1 microgram KLH or CT in alum i.p. Plasma and intestinal secretions were collected at intervals. The specific IgG or IgA antibody in the samples was measured by ELISA. Although KLH feeding did induce oral tolerance, CT feeding did not induce oral tolerance in any of three mouse strains tested or at any dose of CT given orally. The feeding of the B subunit of CT did not result in oral tolerance either. When both CT and KLH were fed together, CT was able to abrogate oral tolerance to KLH, an antigenically unrelated protein. Moreover, feeding CT along with KLH stimulated secretory IgA anti-KLH responses, whereas no such IgA responses were found when KLH was given alone. Thus, in these experiments with protein antigens, IgA immunization and oral tolerance were reciprocally linked and did not occur simultaneously. CT appears to abrogate oral tolerance and to stimulate secretory IgA responses by altering the regulatory environment in gut-associated lymphoid tissue, shifting it toward responsiveness.

Cholera toxin B subunit as a carrier protein to stimulate a mucosal immune response

Horseradish peroxidase (HRP) was covalently coupled to the binding subunit of cholera toxin (CTB) via a two-step glutaraldehyde procedure. The HRP-CTB conjugate was characterized by physiochemical as well as immunochemical methods. Mice were immunized intraduodenally with the HRP-CTB conjugate, with HRP alone, or with a mixture of uncoupled CTB and HRP. The functionally active dose of CTB was 50 micrograms and the HRP dose was in the 30- to 90-micrograms range. Both IgA and IgG antibody responses were measured in serum, intestinal washes, and bile by using a solid phase immunoradiometric assay. Mice immunized with the HRP-CTB conjugate showed a significantly higher level of IgA anti-HRP in intestinal washes and bile, as well as increased levels of serum IgG anti-HRP. Animals that received only HRP or the mixture of CTB and HRP had reduced levels of HRP-specific antibody of either class in both gut washes and bile. The IgA anti-HRP responses in the gut washes were 33- to 120-fold higher when the conjugate was used as the immunogen in comparison with immunization with the CTB + HRP or the HRP alone. Vaccines to stimulate mucosal immunity to any antigenic determinant might thus be prepared by covalent conjugation to effective mucosal immunogens such as CTB.

Generalized systemic and mucosal immunity in mice after mucosal stimulation with cholera toxin

Cholera toxin (CT) has been found to be an extremely potent immunogen for mucosal IgA responses when administered via the intestine. This study has examined both mucosal and systemic immune responses after feeding CT and compared these responses with those obtained after feeding keyhole limpet hemocyanin (KLH), another protein that is strongly immunogenic in mice. Feeding CT to mice resulted not only in IgA antibody in intestinal secretions but also resulted in substantial plasma IgG and IgA antibody levels. Feeding KLH in much larger quantity resulted in little or no antibody response in intestinal secretions or plasma. Lymphoid cells from various tissues of mice fed CT were cultured in vitro for 10 days and the supernatant was tested for antibody to CT. Spontaneous antibody synthesis (no antigen added to cultures) was present in cultures of each cell type, but IgG anti-CT was found mainly in cultures of spleen and mesenteric lymph node cells and IgA anti-CT mainly in cultures of Peyer's patch and lamina propria cells. Peyer's patch cells cultured with CT as antigen synthesized both IgG and IgA anti-CT, suggesting that the antibody response to both isotypes originated in this site. Helper T cell activity for both IgA and IgG anti-CT was detected in spleens, mesenteric lymph nodes, and Peyer's patches. Lastly, when KLH and CT were fed to mice at the same time, an intestinal IgA anti-KLH and plasma IgG anti-KLH response was stimulated, a response pattern similar to that occurring to CT after CT was fed alone. We conclude that mucosal stimulation by CT generates both a systemic IgG and mucosal IgA response to this antigen, and that CT can cause a similar pattern of response to an unrelated protein antigen when both are administered into the intestine at the same time. The data favor the idea that both the IgG and IgA responses originate in GALT and then disseminate to other tissues. We propose that CT accomplishes these effects by altering the regulatory environment within GALT.

Enhanced mucosal priming by cholera toxin and procholeragenoid with a lipoidal amine adjuvant (avridine) delivered in liposomes

The mucosal adjuvant activity of avridine, a synthetic lipoidal amine [N,N-dioctadecyl-N',N'-(2-hydroxymethyl) propanediamine, previously designated CP-20,961), was studied in rats immunized intraintestinally with cholera toxin or procholeragenoid. Avridine was most efficient as an adjuvant when incorporated into liposomes; liposomes that lacked avridine had no adjuvant effect. Coadministration of avridine-containing liposomes with enteric priming doses of cholera toxin or procholeragenoid enhanced the efficiency of priming for secondary mucosal anti-cholera toxin responses, i.e., the establishment of memory, five- to sevenfold. Avridine-containing liposomes had no significant effect, however, on either the primary mucosal anti-cholera toxin response, when given with the primary dose of antigen, or on the secondary response, when given with the booster dose to previously primed animals. Little or no adjuvant effect occurred when avridine-containing liposomes were given concurrently with antigen, but at a separate mucosal site or parenterally, or at the site of enteric immunization, but 1 day earlier or later. These results support the notion that adjuvants may be developed which enhance the mucosal immunogenicity of locally applied antigens and suggest that liposomes may be effective vehicles for delivery of such adjuvants.

Differences in cross-protection in rats immunized with the B subunits of cholera toxin and Escherichia coli heat-labile toxin

Although cholera toxin (CT), Escherichia coli heat-labile toxin (LT), and their B subunits are known to be immunologically related, the ability of each to raise an antitoxin response that provides equally strong cross-protection against active challenge with pure heterologous toxin has not been examined previously. We immunized rats with pure preparations of the B subunits of human LT, porcine LT, and CT. Immunization with either of the LT B subunits raised greater than or equal to fourfold increases in specific mucosal immunoglobulin A antitoxin titers to homologous and heterologous LT and CT B subunits, thereby providing strong protection against active challenge in ligated ileal loops with all three respective holotoxins and with a viable LT-producing E. coli strain. In contrast, immunization with the CT B subunit raised a greater than or equal to fourfold increase in antitoxin titers only to itself and provided strong protection only against challenge with the CT holotoxin. Conjugation of the CT B subunit with the E. coli heat-stable toxin by the carbodiimide reaction yielded a cross-linked immunogen with equal antigenicity for both components; immunization with this conjugate raised greater than or equal to fourfold increases in antitoxin titers to both components, but it provided significant protection only against challenge with a viable heat-stable toxin-producing E. coli strain and not to an LT-producing E. coli strain. These observations indicate that immunization with the LT B subunits raises a heterologous antitoxin response that extends to the CT B subunit, thereby providing equally strong protection against LT and CT; however, immunization with the CT B subunit raises principally a homologous antitoxin response, so that this immunogen provides strong protection only against CT.

Estrogen-like stimulation of uterine ornithine decarboxylase by cholera toxin

Cholera toxin administered by intrauterine injection to ovariectomized rats increased uterine ornithine decarboxylase activity as much as systemic estradiol at 4 h after treatment. At 45-60 min after treatment, however, cholera toxin did not increase nuclear estrogen receptor or stimulate synthesis of the uterine "induced protein," which is closely correlated with nuclear receptor, whereas estradiol caused substantial increases in both nuclear receptor and induced protein synthesis. Intrauterine injection of cholera toxin also produced an estrogen-like elevation of the uterine protein/DNA ratio at 24 h. Because both cholera toxin and estradiol are known to increase vascular permeability, our results support the hypothesis that some uterine effects of estradiol are not mediated by receptor-genome interaction but involve another mechanism that is associated with increased vascular permeability.

A lavage technique allowing repeated measurement of IgA antibody in mouse intestinal secretions

Mouse intestinal secretions can be readily obtained without harm to the mice by administering a lavage solution to them intragastrically followed by pilocarpine intraperitoneally. These secretions are rich in proteases but this enzyme activity can be blocked by addition of a mixture of inhibitors. Both total and specific IgA antibody could be measured in these secretions using ELISA techniques. The total IgA recovered was found to vary considerably, even in the same group of mice sampled on multiple occasions. Specific IgA anti-cholera toxin antibody was easily demonstrable in the intestinal secretions of mice fed cholera toxin but not of mice fed an irrelevant antigen. Expression of the specific IgA antibody per unit of total IgA recovered is desirable in order to correct for the variable recovery of IgA.

[Reactogenicity and immunological effectiveness of a chemical sorbed typhoid vaccine in combination with choleragen-anatoxin administered subcutaneously by jet injector]

The article presents immunological data substantiating the combined immunization of humans with the mixture of choleragen toxoid and chemical adsorbed typhoid vaccine, introduced subcutaneously by means of a jet injector.

Induction of optimal mucosal antibody responses: effects of age, immunization route(s), and dosing schedule in rats

The antitoxin response in intestinal mucosa was studied in rats immunized either intestinally or by combined parenteral and intestinal dosing with cholera toxin or cholera toxoid. Attention was given to the duration of enteric priming and the magnitude and time course of mucosal anti-cholera toxin responses in rats of defined age. Cholera toxin given only intraduodenally was a more efficient priming immunogen in young rats than in older rats and caused priming that lasted at least 32 weeks; repeated enteric doses increased local priming and repeatedly evoked vigorous mucosal anti-cholera toxin responses which occurred rapidly and declined slowly. Results differed when a portion of the immunizing regimen was parenteral. Cholera toxoid given intraperitoneally (i.p.) caused mucosal priming that peaked promptly and then rapidly declined; parenteral boosting after enteric priming was much more effective given i.p. than subcutaneously; moreover, the booster response was brief, virtually disappearing within 11 days, and could not be reproduced by a second i.p. immunization. These results accord with evidence that parenteral immunization both stimulates and suppresses mucosal secretory immunoglobulin A responses, whereas local immunization is not known to be suppressive. Evidence for parenterally induced suppression was the rapid decline in mucosal priming after i.p. immunization, the shortened mucosal antibody response after i.p. immunization, and possibly the inability to parenterally evoke a booster response twice. In these studies, the level of priming observed at different intervals after parenteral, enteric, or combined immunization appeared to reflect the sum of priming and suppressive effects evoked by the preceding immunization(s).

Local and systemic antibody responses and immunological memory in humans after immunization with cholera B subunit by different routes

A single oral or intramuscular immunization with purified cholera B subunit induced an intestinal secretory immunoglobulin A (IgA) antitoxin response in, respectively, 10 out of 11 and 9 out of 12 Bangladeshi volunteers. The IgA titre rise in intestinal lavage fluid was similar by either route of immunization, but the duration of the response was usually longer after the oral dose. A second immunization by either route, given 25 days after the first, and a third dose (oral only), given 15 months later, resulted in intestinal immune responses which did not differ in magnitude from that induced by the initial immunization but were observed significantly earlier, usually by day 3. Both the first oral and intramuscular immunizations induced significant antitoxin titre rises, mainly IgG, in the serum in most vaccinees but the magnitude of the response was considerably higher after the intramuscular dose. Significant IgA antitoxin titre rises in saliva and breast milk were seen after both oral and intramuscular immunization.

Effects of amphotericin B and cholera toxin on intestinal transport in the rat. An in vivo model for the effects of dihydroxy bile acids and fatty acids on intestinal transport

In vivo perfusion experiments were performed in the rat jejunum and colon to test the hypothesis that the changes in intestinal solute transport induced by dihydroxy bile acids and fatty acids are the result of the combined effects of fluid secretion and enhancement of mucosal permeability. The hypothesis predicts that absorption of organic solutes will be reduced in inverse relationship to the absorption rates under control conditions and that absorption of small, nonabsorbable solutes such as mannitol will be enhanced by these agents. Fluid secretion was induced either by administering cholera toxin or by increasing the osmolality of the perfusion solution to 365 mOsm/L. Permeability was enhanced by adding amphotericin B, 50 micrograms/ml, to the perfusion solutions. The isotonic perfusion solutions contained 11.2 mM glucose and 4 mM triethylene, tetraethylene, pentaethylene, and hexaethylene glycol or mannitol as probes of passive permeability. In the jejunum cholera toxin induced fluid and electrolyte secretion and reduced organic solute absorption to a small but significant degree (p less than 0.05). Amphotericin B alone enhanced absorption of organic solutes, water, and electrolytes (p less than 0.01). In the presence of fluid secretion induced by an osmotic load, only absorption of triethylene and pentaethylene glycol was reduced. Addition of amphotericin B after exposure to cholera toxin or to the hypertonic solutions resulted in a further significant reduction of absorption of glucose and ethylene glycols (p less than 0.05). The combination of amphotericin B and cholera toxin resulted in enhanced absorption of mannitol (p less than 0.02). Similarly, 5 mM deoxycholate enhanced jejunal absorption of mannitol (p less than 0.01) and reduced the absorption of glucose and the low-molecular-weight ethylene glycols (p less than 0.01). In the colon the administration of amphotericin B after the exposure to cholera toxin resulted in enhanced absorption of glucose (p less than 0.05) in spite of continuing fluid secretion. The combination of fluid secretion and enhancement of mucosal permeability, therefore, reproduced all in vivo effects of bile acids and fatty acids on intestinal transport of organic solutes.

Conjunctival immunity: compared effects of ocular or intestinal immunization in rats

The ability to induce a conjunctival antitoxin response by conjunctival or enteric administration of cholera toxin antigen was studied in rats. Repeated enteric immunization caused a vigorous jejunal antitoxin response, but none in the conjunctiva. Enteric immunization did, however, prime for a conjunctival antitoxin response to locally applied antigen, as did direct ocular administration of cholera toxin. Vigorous conjunctival antitoxin responses occurred only after ocular challenge, and were localized to the challenged eye. These results agree with the notions that (1) specific memory cells migrate to the conjunctiva after enteric immunization, or arise locally after ocular immunization; and (2) specific antibody-producing plasma cells arise almost entirely within the immunized conjunctiva, and few if any migrate to the conjunctiva from distant mucosae or from the conjunctiva of the immunized eye to that of the nonimmunized eye.

Parenteral immunization causes antigen-specific cell-mediated suppression of an intestinal IgA response

Rats immunized s.c. with cholera toxin (CT) or toxoid (CTd) show antigen-specific suppression of the jejunal IgA anti-CT response to subsequent enteric doses of CT. We determined whether this effect was partly cell-mediated and studied the suppressor cell response involved. Spleen cells from s.c.-immunized rats suppressed the jejunal anti-CT response in adoptive recipients when cell transfer was at, or 4 days before, intraduodenal priming with CT. Transferred suppression was antigen-specific, and the suppressor cells were nylon wool-nonadherent. Increasing the s.c. dose of CT from 0.1 to 40 micrograms, and the interval between immunization and cell harvest from 2 to 16 wk, each increased the suppressive effect of a constant spleen cell inoculum. After s.c. immunization, suppressor cells were present in the spleen within 1 to 2 wk, among TDL within 4 to 8 wk, and in Peyer's patches and thymus within 8 to 16 wk; this sequence suggested they arose in the spleen and later migrated to mucosae and the thymus. Prior splenectomy did not alter the suppressive effect of s.c. CT, however, nor did it prevent suppressor cell appearance among TDL, indicating that suppressor cells also arose from nonsplenic sites. Transferred suppressor cells acted by interfering with the development of specific immunologic memory within Peyer's patches during enteric priming; transfer of suppressor cells at the time of enteric boosting had no effect upon the secondary mucosal anti-CT response. We conclude that the suppressive effect of s.c. immunization on a specific mucosal IgA response is due largely to the action of systemically derived suppressor cells upon the primary mucosal immune response within Peyer's patches. This sequence resembles the mirror image of oral tolerance, which involves the suppression of systemic IgG and IgM responses by suppressor cells that arise in Peyer's patches and migrate to the spleen after antigen feeding.