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.

[Experimental research on cholera vaccines. Local immunity]

Parenteral immunization of rabbits with cholera vaccine decreased the number of Vibrio cholerae adhering to the mucous membrane of the small intestine. Cholera toxoid and the complex preparation ensure protection from the local action of cholera toxin on the ligated loop of the rabbit intestine, while cholera vaccine produces no effect under the same conditions. The use of three preparations under study leads to the decrease of exudative reaction to the introduction of live V. cholerae, the effectiveness of these vaccines growing in the following order: cholera vaccine, cholera toxoid, the complex preparation.

[Distribution of lymphocytes according to the cell cycle phases in T, B, D and O populations in human blood and the immune system organs of animals vaccinated against cholera]

The work presents the results of the study (carried out by the method of continuous flow cytofluorometry) of changes in the distribution of lymphocytes and their populations (obtained by means of distributing cell electrophoresis) according to the phases of the cell cycle (G0 + G1; S; G2 + M) in the blood and spleen of guinea pigs, as well as in the blood of humans, before and after immunization with cholera vaccine. The results of the determination of DNA-synthesizing lymphocytes in the blood of immunized humans and animals have been shown to serve as an objective characteristic for the complex evaluation of the biological activity of cholera vaccines.

Saliva, breast milk, and serum antibody responses as indirect measures of intestinal immunity after oral cholera vaccination or natural disease

The possibility that antibody responses in serum, saliva, or breast milk samples to oral vaccines or enteric infections may reflect the intestinal immune response was evaluated in Bangladeshi volunteers orally immunized with a cholera B subunit-whole-cell vaccine (B + WCV) and in patients convalescing from enterotoxin-induced diarrheal disease. Two peroral doses of B + WCV induced antitoxin and antibacterial antibody responses in the intestinal fluids of 76 and 92%, respectively, of the volunteers and in serum samples in 90 and 69% of those tested. These responses were comparable to those obtained after cholera or enterotoxigenic Escherichia coli disease. Whereas immunoglobulin A (IgA) antitoxin titer increases in saliva (44%) and breast milk (29%) specimens after vaccination were less frequent than in intestinal fluid (76%), antitoxin responses in saliva and breast milk occurred in 80 to 90% of the patients after disease. Also, antilipopolysaccharide (anti-LPS) titer increases in extraintestinal body fluids were found more frequently after disease than after vaccination. A comparison of the frequency and magnitude of antibody response in different body fluids with those in intestinal lavage fluid revealed no extraintestinal antibody that directly reflected the intestinal immunity. However, comparison of vibriocidal and IgG antitoxin antibodies in serum specimens with antitoxin and anti-LPS IgA responses in intestinal fluids after the vaccination of volunteers showed a sensitivity of 70 to 90% and a predictive accuracy of about 80% for the serum analyses reflecting the intestinal immune responses. Furthermore, antitoxin and anti-LPS antibody responses in saliva and breast milk samples seemed to be useful proxy indicators of a gut mucosal response of these antibodies after enterotoxin-induced diarrheal disease showing sensitivity vales of 70 to 90% and predictive accuracy vales of 70 to 100%.

Molecular cloning and expression in Escherichia coli K-12 of the O antigens of the Inaba and Ogawa serotypes of the Vibrio cholerae O1 lipopolysaccharides and their potential for vaccine development

The gene clusters that determine the biosynthesis of both the Inaba and Ogawa serotypes of the O antigen of the lipopolysaccharide of Vibrio cholerae were cloned and expressed in Escherichia coli K-12. Restriction analysis of the clones demonstrated that about 15 kilobases were common to all clones and a further 5 kilobases were common to the Ogawa clones. The O antigens expressed by E. coli K-12 had the specificity of V. cholerae. Antibodies raised against E. coli K-12 that harbor one of these clones, pPM1001 (Inaba), were as highly protective in the infant mouse model system as were antibodies to V. cholerae itself. Introduction of such clones into suitable carrier strains could be expected to produce a good oral immunogen against cholera.

[Effect of dexamethasone-A synthetic glucocorticoid hormone on the immune response in pigs]

These experiments were designed to study the effects of a synthetic drug--dexamethasone (DEX) on the immune response of weaned pigs against viral antigen (hog cholera vaccine) and bacterial antigen (formalin inactivated Salmonella enteritis vaccine). Twenty-three five-week-old pigs were divided into eight groups, six of which were injected twice daily with DEX at 1.0 mg or 0.1 mg per Kg of body weight for either four or five days. The other two groups served as controls. During this period, the two 0.1 mg/Kg DEX-treated groups were injected with live hog cholera vaccine at 1.0 or 0.1 dosage respectively. This same treatment was applied to the two 1.0 mg/Kg DEX-treated groups. One control group was injected with a dose of hog cholera vaccine, while the other was given 1.0 ml of Sal. enteritis vaccine. The hog cholera antibody response in DEX-treated pigs was significantly suppressed (p less than 0.01). However, consistent levels of antibody titers were maintained, indicating a slight antibody production. But in pigs injected with one tenth of the normal dose of hog cholera vaccine, there was little or no immune response (p less than 0.01). A comparison of the response of pigs given different levels of DEX concentrations to those with different doses of hog cholera vaccine showed that dexamethasone significantly suppressed antibody production when antigen concentrations were lower. Significant suppression of agglutinating antibody in response to bacterial antigen was also observed at 14 days post-vaccination (p less than 0.05).

Vibrio cholerae infection and acquired immunity in an adult rabbit model

We modified the rabbit model for enteric infection by Vibrio cholerae developed by Spira et al. and designated the RITARD (for removable intestinal tie-adult rabbit diarrhea) model (20). Our modification DISC comprises a permanent ligation of the cecum (C) to prevent resorption of the fluid secreted by the small intestine, a temporary ligation of the small intestine (S) to enable the bacteria to colonize, and duodenal inoculation (DI) of the challenge material. The main difference between RITARD and DISC is that in the latter model the challenge material is injected into the duodenum approximately 10 cm distal to the stomach instead of into the jejunum. Four out of 5 V. cholerae strains tested, including 2 serotypes and 2 biotypes, were able to elicit a massive and usually fatal cholera-like diarrhea. The virulence depended strongly on the culturing conditions. One strain, C5, caused fatal diarrhea in a dose of about 1000 organisms, even if the temporary ligation was omitted (DIC model). Other modifications were the DIS and the DI model in which the permanent ligature of the cecum or both ligatures were omitted. Duodenal inoculation of organisms in a dose of 100 X the minimum infective dose (MID) in the DIS or DI model did not cause any disease symptom. However, such inoculations were found to cause protection against subsequent challenges with 100 X MID of homologous and heterologous organisms up to 52 weeks after duodenal inoculation. Subcutaneous injection with classical, whole cell cholera vaccine gave only partial protection of short duration. This model might contribute to the understanding of the pathogenesis of cholera as well as to the improvement of efficacy testing of cholera vaccines.

The immune response of the mammary gland and its significance for the neonate

The immune response of the mammary gland is dominated by local production of secretory IgA antibodies (SIgA). These milk antibodies, amounting to about 0.5-1 g/day throughout lactation, are directed against food proteins and microorganisms often present in the intestine. This is presumably explained by the enteromammaric link: after antigenic exposure in the Peyer's patches of lymphoid cells they home to various exocrine glands, including the mammary gland. Similarly, lymphoid cells from the bronchial mucosa, may contribute to the antibody-producing cell population in the mammary gland. SIgA antibodies against common foods like cow's milk and soy proteins are regularly found in milk if such proteins are part of the mother's diet. It is possible, but unproven, that milk antibodies can decrease the exposure of the infant's intestinal mucosa to foreign food proteins introduced during continued breast-feeding. Milk SIgA antibodies do not prevent intestinal colonization by microorganisms, against which the milk antibodies are directed. The SIgA antibodies are thought to exert protection primarily by preventing contact between the microorganisms and the mucosal membranes. In this manner, human milk blocks attachment of otitis media-causing strains of pneumococci and H. influenzae to retropharyngeal cells, possibly explaining why breast-feeding may prevent otitis media. Milk antibodies have anti-attachment capacity, but there is also low molecular weight material in the milk with this capacity. It probably consists of analogues to the oligosaccharide receptor for pneumococci on the retropharyngeal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

[Standardization of cholera vaccine and preparation of a national reference standard]

The antigenic potency of the proposed national reference preparations in comparison with that of the corresponding international reference preparations was studied by means of the active protection test in mice. The antigenic potency of the proposed national reference preparations for Inaba and Ogawa was found to be the same or even greater than the antigenic potency of the international reference preparations for cholera vaccine. A high level of antigenic activity was observed during comparison of a production lot of cholera divaccine with the international reference preparation and the national reference preparation in parallel tests. The proposed national reference preparations for Inaba and Ogawa may be used for evaluating the antigenic potency of the lot of cholera vaccine produced in Bulgaria as the standard preparation.

From the National Institute of Allergy and Infectious Diseases. Summary of the 19th United States-Japan Joint Cholera Conference

Classical cholera has reappeared in Asia after a 20-year hiatus, reminding us that we still have much to learn about the epidemiology of this disease. The unexpected recovery of V. cholerae from nonendemic estuarine waters suggests that the continued occurrence of clinical cholera may not be entirely dependent on repeated contamination of environmental waters by man. Of critical importance has been the discovery and partial characterization of new enterotoxins produced by V. cholerae and ETEC, a finding that further complicates the already complex problem of fully elucidating the virulence mechanism of these organisms. The recent purification of Shiga toxin is beginning to provide clues as to its structure, function, and possible pathogenic role in EPEC-related hemorrhagic colitis and diarrhea. The conversion of virulent V. cholerae into less virulent strains by genetic engineering provides hope for the ultimate development of safe and effective live oral cholera vaccines. Intestinal Peyer's patches process living and killed enteropathogens differently, and this discovery may afford insights into ways to improve antigen potency. Enterotoxins differ fundamentally in their biochemical effects, and not all of them evoke active electrolyte secretion by altering cyclic-nucleotide levels in mucosal cells. Finally, the mucosal response to a protein toxin may be under some genetic control. The complete proceedings of this conference will be published by KTK Publishers (Tokyo). The next Joint Conference on Cholera has been scheduled for early November 1984 in Nara, Japan.

Mucosal antitoxic and antibacterial immunity after cholera disease and after immunization with a combined B subunit-whole cell vaccine

Mucosal and systemic immune responses to a new oral cholera vaccine, consisting of the B subunit plus killed vibrios, were studied in Bangladeshi volunteers and compared with those to clinical cholera. A single peroral dose of vaccine induced a local IgA antitoxin response in intestinal-lavage fluid of seven of eight vaccinees; the response closely mimicked that of patients convalescing from cholera, and evidence of the induction of local immunologic memory was found as well. Two peroral doses were needed for stimulation of an intestinal IgA immune response to the lipopolysaccharide of Vibrio cholerae that was comparable to the response obtained after clinical cholera. This response to peroral immunization was considerably stronger than that to parenteral vaccination, although the intramuscular route gave rise to the strongest IgG antitoxin and antilipolysaccharide responses in serum. The results suggest that B subunit-whole cell vaccine, when given in at least two oral doses, may be a good candidate for use in cholera prophylaxis.

Modulation of antibody responses to Vibrio cholerae in mice by adoptive transfer of Peyer's patch lymphocytes from orally immunised donors

Peyer's patch lymphocytes from mice orally primed with V. cholerae injected into recipient mice together with V. cholerae led to a considerable suppression of IgM antibody-forming cells in the spleen by comparison with control mice receiving the same schedule but with Peyer's patch lymphocytes from unprimed mice. The effect on the splenic IgA responses of recipients was variable. Incomplete separation of the Peyer's patch cells showed that both T and B cell enriched fractions were active in this suppressive effect.

Effect of chemical and heat inactivation on the antigenicity and immunogenicity of Vibrio cholerae

The effects of heat and chemical inactivation on the antigenicity and immunogenicity of Vibrio cholerae 1418 in rabbits were studied. V. cholerae 1418 was inactivated with heat and chemical inactivants (phenol or Formalin) alone or in combination. Enzyme-linked immunoassay systems employing whole cells of V. cholerae 1418, lipopolysaccharide, or flagella as immobilized antigens were used to measure the antibody response (immunoglobulins G and M) after parenteral immunization of rabbits with various inactivated whole-cell preparations. The "classical" whole-cell vaccine, produced by phenol treatment, was found to be a comparatively poor immunogen. When Formalin was used instead of phenol, the antibody response to all three enzyme-linked immunosorbent assay antigens was greatly increased. Immunoglobulin G titers to intact V. cholerae cells were as much as 100-fold higher in rabbits immunized with the Formalin-inactivated preparation as compared to the classical phenol-inactivated vaccine. Furthermore, antibody produced against the Formalin-inactivated preparation was capable of recognizing antigenic determinants expressed on the cell surface of several heterologous strains of V. cholerae. These results indicate that the antigenicity and immunogenicity of V. cholerae are greatly affected by the inactivation conditions employed for vaccine production and that Formalin is much superior to phenol as an inactivant under the conditions employed in the present study.

Protection in rabbits induced by the Texas Star-SR attenuated A-B+ mutant candidate live oral cholera vaccine

The avirulent, A-B+, streptomycin-resistant mutant designated Texas Star-SR, isolated from a virulent, hypertoxinogenic, colonizing strain of Vibrio cholerae (Ogawa serotype, El Tor biotype) and administered intragastrically or intraduodenally in adult rabbits, has been found to induce substantial immunity to subsequent challenge (in ligated intestinal loops) with virulent wild-type cholera vibrios (of both homologous and heterologous biotype and serotype). Significant resistance to challenge with one strain of human heat-labile enterotoxin (LT)-producing Escherichia coli was also demonstrated, but resistance against two other human LT-producing strains was either nil or marginal under these experimental conditions. Significant, but not striking, resistance against challenge with purified choleragen was obtained, whereas protection against a bolus challenge of purified porcine LT was not statistically significant.

[Energy allowance for antibody formation in rabbits immunized with cholera vaccine and by exposure to tetracyclines]

Oxidative phosphorylation and succinate dehydrogenase activity in liver mitochondria, as well as activity of glucoso-6-phosphate dehydrogenase in liver homogenates were studied on 126 rabbits immunized with cholera vaccine and exposed to tetracycline or doxycycline (vibramycin). It was found that tetracycline and especially doxycycline inhibited the bioenergy processes in both intact and immunized animals. The inhibitory effect of doxycycline was most pronounced in the immunized rabbits. The shifts in the titers of the specific antibodies under the experimental conditions directly correlated with the state of the endocellular oxidation-reduction processes.

Development of a vaccine against experimental cholera and Escherichia coli diarrheal disease

The results of the present investigation indicate a simple approach to the development of a single-vaccine formula which may ultimately be used to confer protection against both cholera and certain types of Escherichia coli diarrheal disease in humans and domestic animals. The design of the vaccine is based on the well-documented ability of cholera antitoxin to neutralize both cholera and heat-labile E. coli enterotoxins (CT and LT, respectively) and on the ability of killed E. coli to enhance the immune response to cholera toxoid and, possibly, to conventional cholera vaccine as well. Evidence presented shows that a parenterally administered E. coli vaccine, prepared from an LT-only enterotoxigenic strain, reproducibly elevated rabbit antitoxin responses to cholera toxoid and that such responses correlated with dramatic protection against live cholera vibrios and the homologous E. coli strain in the rabbit ligated loop model of diarrheal disease. The results show also that cholera vaccine acted to suppress the rabbits' immune response to the cholera toxoid and E. coli vaccine formula, even though all three antigens combined still provided significant protection against live organism challenge. On the basis of data presently available, the vaccine formula would be composed simply of cholera toxoid and E. coli vaccine, but may also include cholera vaccine. Since it has already been established that cholera toxoid and cholera vaccine are each safe for human use, additional vaccine development would require investigation of the safety of E. coli vaccine, alone and in combination with the other components.

Different secretory immunoglobulin A antibody responses to cholera vaccination in Swedish and Pakistani women

The capacity of subcutaneous cholera vaccination to induce an antibody response in milk and saliva was studied in lactating Swedish and Pakistani women, since secretory immunoglobulin A (SIgA) antibody responses in these secretions may reflect intestinal immunity. Before immunization, most of the Pakistani women had significant titers of specific SIgA antibodies against Vibrio cholerae lipopolysaccharide in milk, whereas only a few of the Swedish women had measurable, low titers. In the Pakistani women a single subcutaneous injection of cholera vaccine gave rise to a significant SIgA titer rise in 70% of the milk and 45% of the saliva samples. The Swedish women, on the other hand, did not respond with a significant antibody response of any immunoglobulin class in milk or saliva, either after a single or after a booster dose 14 days later. In serum, however, the vaccination induced significant titer rises, mainly of IgG antibodies, also in the Swedish women, but these rises were of lower magnitude than those in the Pakistani group. The results suggest a significant difference in the capacity of parenterally administered cholera vaccine to stimulate SIgA antibody formation in naturally primed and nonprimed individuals.

Improved protection against cholera in adult rabbits with a combined flagellar-toxoid vaccine

Ligated ileal loops of adult rabbits were used to evaluate the prophylactic potential against cholera of a combined vaccine consisting of toxin-free crude flagella (CF) and glutaraldehyde-derived cholera toxoid (TV). The resulting fluid accumulation ratios were compared with those in rabbits immunized with saline (controls) and with CF and TV alone. Data for single vaccines confirmed the superior protection effect of CF over TV. In rabbits vaccinated with both CF and TV, maximal fluid accumulation ratios were not obtained with a challenge dose as high as 5 X 10(9) colony-forming units (CFU). Two rabbits similarly immunized failed to produce positive loops with challenges of 6.3 X 10(8) and 5 X 10(9) CFU, respectively. The vibriocidal titer of serum from rabbits immunized with a killed commercial vaccine in addition to those listed above was determined at intervals for a period of 164 days. No vibriocidal activity was detected in serum of control rabbits and of rabbits vaccinated with TV. Serum from animals given CF or commercial vaccine had similar vibriocidal titers even when the test bacteria were nonflagellated. Protection against challenge as evaluated by ileal loops did not, however, correlate with vibriocidal titer.

Assessment of antibody responses and protective immunity in cholera vaccinated subjects

Cross-reactive antibody responses were assessed in volunteers vaccinated with classical Inaba and Ogawa cholera vaccines. The El Tor, Ogawa vibrios, the most often biotype, and serotype found to be the causative agent of cholera in Thailand, or their product were used throughout the in vitro and in vivo tests. The test involved were the passive hemagglutination test, vibriocidal tests and the mouse protection test. Classes of specific immunoglobulins produced in the volunteers were determined using anti-immunoglobulin enhancement of hemagglutination. It was found that the levels of hemagglutinating and vibriocidal antibodies reached their peaks on day 7 after the vaccination and were statistically constant for 3 months. Significant decrease was observed thereafter. The mouse protective antibody titer was highest at 1 month after the vaccination then declined significantly at the 6th month. Classes of specific immunoglobulins were found to be either IgM or IgG alone or mixture of both.

Synergistic protection against experimental cholera by immunization with cholera toxoid and vaccine

Rabbits were immunized with two parenteral injections of Wellcome toxoid PX389A, Wyeth toxoid 20101, or Merck bivalent vaccine. Other groups of rabbits were immunized with combinations of the Merck vaccine and each of the two toxoids. Antitoxin responses were monitored in each group of rabbits before livecell challenge of each animal by the ligated intestinal loop assay. Inaba and Ogawa strains of Vibrio cholerae were used for challenge experiments. Basically, the data indicate that the toxoids were equivalent in antigenic potency and antitoxin responses were unaffected by combination of the toxoids with the whole-cell vaccine. The 50 microgram doses of each toxoid as well as the 4 X 10(9) cells of the bivalent vaccine provided the same magnitude of protection against live-cell challenge with either Inaba or Ogawa vibrios. Immunization with either toxoid in combination with the bivalent vaccine resulted in a synergistic protective response against live-cell challenge of intestinal loops with V. cholerae. Synergistic protection was observed when toxoid and vaccine were administered together by the oral and parenteral routes. Maximum protection was obtained when rabbits were immunized with the combined toxoid-whole-cell vaccine administered by both oral and parenteral routes.

Flagella-induced immunity against experimental cholera in adult rabbits

The adult rabbit ligated ileal loop model was used to evaluate the prophylactic potential of a crude flagellar (CF) vaccine produced from the classical. Inaba strain CA401. A greater than 1,000-fold increase in the challenge inoculum was required to induce an intestinal fluid response in actively immunized adult rabbits equivalent to that produced in unimmunized animals. Similar protection was afforded against challenge with classical and El Tor biotypes of both Inaba and Ogawa serotypes. Highly virulent 35S-labeled vibrios were inhibited in their ability to associated with the intestinal mucosa of CF-immunized rabbits. The protection conferred by CF immunization was found to be superior to that of a commercial bivalent vaccine and also to that of glutaraldehyde-treated cholera toxoid. The critical immunogenic component of CF appears to be a flagella-derived protein. The immunogenicity of CF was destroyed by heat treatment, and absorption of CF-immune serum with aflagellated mutant vibrios did not diminish its ability to confer a high level of passive protection. The intestinal protection of CF-immunized rabbits was completely reversed by the introduction of both goat anti-rabbit immunoglobulins A and G, but by neither alone.

[The role of immunization against bacterial enteric infections (author's transl)]

The author reviews critically the available vaccines against salmonellosis and shigellosis, the more sophisticated vaccines against these two infections and cholera presently under experimentation and using parenteral or oral dispensing. To contribute to public health planning, with particular reference to developping countries, the authors points on the necessity to evaluate carefully the merits of the different techniques aiming at controling bacterial enteric infections. Sanitation seems to be the most effective and the less expensive technique.

Persistence in the mouse gut as an important factor in oral immunogenicity of strains of V. cholerae

The immune responses of mice following oral vaccination with two strains of live V. cholerae have been examined. A strain which persisted in the small intestine was a superior local immunogen by comparison with another non-persisting strain. Local persistence and the ability to induce a local immune response appeared to be correlated, since the two vibrio strains elicited identical responses when given parenterally.

The suppressive effect of circulating specific antibody on the response to oral immunisation with Vibrio cholerae

Species IgG antibody given intravenously 3-4 hours prior to oral immunisation with Vibrio cholerae led to a specific depression of both the systemic and loca limmune response. One vibriocidal unit of IgG antibody, which itself would given undetectable levels of circulating specific antibody, was significantly immunosuppressive. The suppression is considered to be due to central repression of the antigen-reactive lymphocyte, rather than to antigen exclusion at the gut mucosal surface. The repression appeared less pronounced in some immunoglobulin classes than in others.

Antigenicity testing of plain and aluminium hydroxide-adsorbed whole-cell cholera vaccines

The antigenicity of a plain and of an aluminium hydroxide-adsorbed whole-cell cholera vaccine was investigated by the active mouse protection test and the vibriocidal antibody production assay in mice. In the active mouse protection test, between the antigenicity of the Inaba and Ogawa component of the two vaccines was no significant difference. The antibody production test, however, revealed that the adsorbed vaccine elicited higher and longer lasting immune response than the plain one. The antibody response to a two-dose immunization schedule was substantially superior to that after a one-dose schedule.

Local immune response in mice to Vibrio cholerae

Cholera immunization schedules were investigated in mice, with emphasis placed on obtaining an immune response in the intestine. The most effective schedule for producing a good local response was found to be several orally-given priming doses of the organism followed after 14 days by an intravenous boosting dose. Major differences between the immune responses in the spleen and the intestine were noted.

[Immunogenic properties of cholerogen-toxoid and killed corpuscular vaccine in acute experiments on guinea pigs]

A comparative assessment of the immunogenicity of cholerogen toxoid and of killed corpuscular cholera vaccine was given. Guinea pigs immunized with cholerogen toxoid acquired a greater resistance to the intrapulmonary infection with virulent cholera vibrio culture (immunity index--2.1.10(4)) than those immunized with killed corpuscular vaccine (immunity index--3.5.10(2)). Immunogenicity of cholerogen toxoid could be increased in its combined administration with killed corpuscular vaccine.

Motility of the pathogen and intestinal immunity of the host in experimental cholera

1) Motility seems to be required for an intimate association with the intestinal mucosa which is necessary for efficient toxin delivery in the pathogenicity of V. cholerae. 2) A vaccine of semipurified flagella (CF) afforded a high degree of active and passive immunity in the rabbit ileum to both homologous and heterologous challenge strains. 3) The nature of the immunoglobulin type involved in the active immunity elicited by CF was not clear but preliminary indications implicate both s-IgA and IgG.

Secretory IgA antibodies to enterobacterial virulence antigens: their induction and possible relevance

1) Milk and salivary s-IgA antibodies are via the homing of IgA producing cells from the Peyer's patches closely connected with antigenic stimuli in the intestine. This explains the presence in human milk of s-IgA antibodies against E. coli O and K antigens, V. cholerae and Shigella O antigens, E. coli and V. cholerae enterotoxins. These secretory antibodies can be induced by intestinal exposure and boosted by parenteral vaccination. 2) Preliminary data suggest that the IgA response in the urinary tract and possibly in the lung may be involved in the homing mechanism as well. 3) The protective role of the milk s-IgA antibodies to enterobacterial virulence antigens is strongly suggested, as is the protection mediated by urinary antibodies against urinary tract infections.