Local (immunoglobulin A) immune response by the intestine to cholera toxin and its partial suppression with combined systemic and intra-intestinal immunization

Mucosal immunity to poliovirus

A cornerstone of the global initiative to eradicate polio is the widespread use of live and inactivated poliovirus vaccines in extensive public health campaigns designed to prevent the development of paralytic disease and interrupt transmission of the virus. Central to these efforts is the goal of inducing mucosal immunity able to limit virus replication in the intestine. Recent clinical trials have evaluated new combined regimens of poliovirus vaccines, and demonstrated clear differences in their ability to restrict virus shedding in stool after oral challenge with live virus. Analyses of mucosal immunity accompanying these trials support a critical role for enteric neutralizing IgA in limiting the magnitude and duration of virus shedding. This review summarizes key findings in vaccine-induced intestinal immunity to poliovirus in infants, older children, and adults. The impact of immunization on development and maintenance of protective immunity to poliovirus and the implications for global eradication are discussed.

The Importance of Animal Models in the Development of Vaccines

Efficient translation of basic vaccine research into clinical therapies greatly depends upon the availability of appropriate animal models. Testing novel vaccine candidates in animal models is a critical step in the development of modern vaccines. Animal models are being used to assess the quality and quantity of the immune response, to identify the optimal route of delivery and formulation, to determine protection from infection and disease transmission, and to evaluate the safety and toxicity of the vaccine formulation. Animal models help to make the translation from basic research to clinical application, and they often allow prediction of the vaccine potential, which helps in predicting the financial risks for vaccine manufacturers. Choosing an appropriate animal model has become increasingly important for the field, as each model has its own advantages and disadvantages. In this review, the criteria for selecting the right animal model, the advantages and disadvantages of various animal models, as well as the future needs for animal models are being discussed.

Mucosal immunity and gastrointestinal antigen processing

The intestine is the largest lymphoid organ in the body by virtue of lymphocyte numbers and quantity of immunoglobulin produced. This is largely related to the enormous antigen load to which these cells are exposed on a daily basis. However, despite this, the mucosa-associated lymphoid tissue appears to be regulated by unique mechanisms, and this is reflected in specific phenomena (oral tolerance, controlled or physiologic inflammation) as well as unusual lymphoid populations (intraepithelial lymphocytes) that respond to alternative pathways of activation. This, coupled with the existence of novel antigen-presenting cells (intestinal epithelial cells) sets the scene for distinct immune responses. It is these distinct regulatory factors that support immunosuppression or tolerance rather than active immunity at a site juxtaposed to the external environment. This review defines these novel interactions and suggests how alteration in normal function may result in allergic or inflammatory responses. A clearer understanding of mucosal immunoregulation may lead to new therapeutic approaches for these diseases.

Protective effect of administration of skim milk on exogenous and endogenous infection in mice

In order to minimize the denaturation of proteins in milk, normal cow's milk was pasteurized at 61 C for 20 min. The protective effects of the thus prepared skim milk (low-heat skim milk) on exogenous and endogenous infection were examined as compared with conventional skim milk which was pasteurized at 121 C for 2 sec. The antibody titers to Listeria monocytogenes and Escherichia coli of low-heat skim milk were almost equal to that of raw milk, while no antibody was detected in the conventional skim milk. When mice were given low-heat skim milk or conventional skim milk, the incidence of the translocation of orally inoculated Listeria monocytogenes to the spleen was lower in the low-heat skim milk group than that in the conventional skim milk group. The life span of 7 Gy X-ray irradiated mice given low-heat skim milk was significantly prolonged in comparison to that of mice given conventional skim milk. However, there were no differences in the number of bacteria in the feces or IgA production by Peyer's patch cells between the two groups. These results suggest that antibodies in low-heat skim milk, which still have reactivity to exogenous or indigenous bacteria, may contribute to the protective effects against bacterial infection.

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.

Immune responses in chickens against Salmonella typhimurium monitored with egg antibodies

Three mature hens were immunized with an Aro- mutant of Salmonella typhimurium beginning with a subcutaneous dose in adjuvant followed by two oral boosters. Isotype-specific antibodies were measured in the white and yolk eggs collected weekly over a period of 230 days. Two hens showed a memory response to the first oral booster, with large increases in egg yolk IgG and smaller increases in IgA and IgM antibodies in egg whites. Smaller amounts of IgA and IgM antibodies were found in egg yolks, and a slight increase in IgG occurred in the whites. One hen showed an increase in serum titers of all isotypes against S. typhimurium. The second hen had high serum titers before immunization was started which did not change. The third hen had a high level of IgM in the white of eggs before immunization was started. This hen showed erratic responses in egg white antibodies following immunization, no increase in IgA or IgM in yolks and only a slight increase in IgG, no increase in serum IgG, and was the only hen with a high level of IgM antibody against S. typhimurium in the bile, conditions reflecting a state of oral tolerance. With the exception of this hen, the results showed that IgA and IgM antibodies were aroused in hens by immunization with an avirulent mutant of S. typhimurium, and that these antibodies were present in the white of eggs from immunized hens.

Anti-cholera toxin IgA-, IgG- and IgM-secreting cells in various rat lymphoid tissues after repeated intestinal or parenteral immunizations

Single antibody-secreting spot-forming cells (SFC) of the 3 main isotypes were counted in lymphoid cells from the gut lamina propria (LP), Peyer's patches (PP), mesenteric nodes (MN) and spleen (SP) of rats immunized 2-6 times intraduodenally (ID) or intraperitoneally (IP) with cholera toxin (CT). Responses for all isotypes peaked in all tissues after 4 ID- or IP-immunizations at much larger values than previously reported, and significantly decreased thereafter, except in LP and PP after IP-injections, where IgA- or IgG-SFC, but not IgM-SFC, only appeared or increased after 6 IP-doses. The highest IgA-SFC numbers (17% of tested cells) were in LP after 4 ID-doses. The isotype ratio was IgA greater than IgG greater than IgM in LP and PP after ID-injections, but IgG greater than IgA greater than IgM in MN and SP after both ID- and IP-routes. The isotype dispersion was much larger in LP and PP than in MN and SP. Our data show that at least 4 IP CT-doses were required to only elicit a few IgG- and almost no IgA-SFC in LP and PP, outlining the need for intestinal CT-immunizations to induce strong mucosal IgA-SFC responses. We also show good systemic responses elicited both by enteral and parenteral routes, and the small contribution of PP in total SFC, particularly after parenteral immunizations.

Secretory immunoglobulin A response to Shiga toxin in rabbits: kinetics of the initial mucosal immune response and inhibition of toxicity in vitro and in vivo

Although the role of Shiga toxin in dysentery is unknown, the toxin is cytotoxic to HeLa cells, causes fluid secretion in rabbit intestine, and is lethal to rabbits and mice when injected parenterally. In the present study, rabbits received three weekly doses of Shiga toxin directly into chronically isolated ileal loops. Within a week, secretions from these loops contained immunoglobulin A (IgA) anti-Shiga toxin. The titer of IgA anti-Shiga toxin increased after weekly doses 2 and 3. Little IgG anti-Shiga toxin was present in loop secretions, although high titers of IgG anti-Shiga toxin were found in the sera. These loop secretions were able to neutralize the cytotoxic effects of Shiga toxin in the HeLa cell assay. The capacity to neutralize the cytotoxicity of the toxin correlated strongly with the IgA anti-Shiga toxin titer in these same secretions. Pooled immune loop secretions were also able to significantly reduce fluid accumulation in acutely ligated loops in rabbits, while loop secretions from control rabbits could not. Shiga toxin elicited a strong secretory IgA response upon application to the intestine. Further, the mucosal antibodies produced functioned to prevent the toxic effects of Shiga toxin both in vitro and in vivo.

Reduction of intestinal carcinogen absorption by carcinogen-specific secretory immunity

A secretory immune response to the carcinogen 2-acetylaminofluorene (AAF) was elicited in rabbits by directly immunizing the small intestine with an AAF-cholera toxin conjugate. High-titer, high-affinity secretory immunoglobulin A (IgA) antibody to AAF was secreted into the intestinal lumen in response to this immunogen. Immune secretions reduced the transepithelial absorption of a 125I-labeled derivative of AAF by more than half. This reduction of absorption by hapten-specific IgA suggests that oral vaccines against carcinogens and toxicants could be developed for humans.

Combined parenteral and oral immunization results in an enhanced mucosal immunoglobulin A response to Shigella flexneri

Achieving a vigorous secretory immunoglobulin A (IgA) response in intestinal secretions usually requires multiple doses of antigen given orally, while systemic immunity is more easily attained by parenteral immunization. This study examines the role of combined parenteral and oral immunizations to enhance the early mucosal immune response to an enteropathogen. We have used a chronically isolated intestinal-loop model in rabbits as a probe to monitor kinetically the initial (primary) local immune response to shigella lipopolysaccharide (LPS) following combinations of parenteral immunization intramuscularly (i.m.) and oral stimulation with shigellae. Predictably, effective stimulation of systemic immunity was elicited when heat-killed preparations of Shigella sp. strain X16 were given i.m., as shown by strong serum IgG and weak intestinal IgA activity to shigella LPS. A single oral dose of live Shigella sp. strain X16 given to unprimed rabbits elicited only a typical weak IgA response in intestinal secretions. However, when an i.m. dose of heat-killed shigellae was followed 1 day later by an oral dose of live Shigella sp. strain X16, a hyperstimulation of the early secretory IgA response was elicited, and the response reached levels found previously only after multiple oral administrations of live shigellae. This stimulation did not require the use of an adjuvant. At the same time, the animals receiving this combined oral and i.m. regimen had a lower IgG antishigella LPS activity in serum compared with their response after receiving parenteral antigen in adjuvant alone. These findings indicate that while a dichotomy exists between the systemic and mucosal immune responses, careful orchestration of the stimulatory events can promote a vigorous early local IgA response.

Neutrophil mediated and IgA dependent antibacterial immunity against enteropathogenic Escherichia coli in the porcine intestinal mucosa

The role of polymorphonuclear neutrophils (PMN) in the antibacterial immunity against enteropathogenic Escherichia coli (EEC) 0:149 in the porcine intestine was studied using intestinal Thiry-Vella loop (T-V loop) as a model. Intraluminal immunizations of T-V loops resulted in elevated levels of immunoglobulin A (IgA) anti-EEC 0:149 antibody in the loop secretions, an infiltration of PMN in the lumen of the loops and an increase in the concentrations of lactoferrin (LF), lysozyme (LY), cationic proteins (CP), and a specific bactericidal response in the immunized loops. PMN were observed by electron microscopy (EM) to be actively phagocytic in the lumen of the immune loops. EM observations of loop fluids as well as the abrogating effect of iron on the in vivo bactericidal response strongly suggest that the pMN played an important role in the bactericidal response in the loops against EEC. In addition to phagocytosis by PMN and subsequent intracellular killing, disintegration of PMN in the lumen of the loops and extracellular killing of EEC by the antibacterial products of PMN such as LF, LY and CP, with and/or without synergistic effect of IgA antibodies, also contribute to the bactericidal response of the immunized loops.

Effect of antigen form on local immunoglobulin A memory response of intestinal secretions to Shigella flexneri

An enhanced memory response, as shown by increased titers of specific immunoglobulin A (IgA), was seen in intestinal secretions from isolated Thiry-Vella loops in rabbits primed orally with live, locally invasive Shigella sp. X16 and challenged 60 days later with a single oral dose of the same antigen. Heat-killed shigella preparations, when used as either the priming or challenge antigen, did not elicit such a memory response in this system. In the present study, the role of antigen form and dosage in eliciting the enhanced local IgA response was investigated. A noninvasive strain, Shigella flexneri 2457-0, was capable of significantly enhancing the mucosal IgA memory response, whereas heat-killed Shigella sp. X16 was unable to augment the local IgA response, even when the priming dose was increased 100-fold. A proposed mucosal adjuvant, DEAE-dextran, given orally with live Shigella sp. X16, did not enhance the local IgA response. Viable, noninvasive shigellae were effective priming agents in enhancing the local IgA memory response. The poor mucosal response to heat-killed shigella preparations is thought to be related to an ineffective delivery of nonviable bacterial antigens into gut-associated lymphoid tissues. The ability of the live, noninvasive strain to elicit a vigorous local IgA memory response when given orally to rabbits was consistent with previous findings that live preparations elicit the best mucosal IgA response.

Hymenolepis microstoma: mouse strain differences in resistance to a challenge infection

Antibody responses and host resistance to the tapeworm, Hymenolepis microstoma, were investigated using AKR/J and C3HeB/FeJ strains of mice. AKR mice were significantly more resistant than controls to a secondary infection following exposure to a 3-, 21-, or 40-day primary infection. During a primary infection, intestinal anti-worm antibody responses measured by an enzyme-linked immunosorbent assay were elevated in the more resistant AKR strain, whereas serum antibody titers did not differ between the two strains. However, during a secondary infection, serum IgA titers were higher in AKR mice than C3H mice. Suppression of the serum IgA anti-worm response by oral administration of lipopolysaccharide also suppressed resistance to a secondary infection. Intraperitoneal immunization with worm antigen resulted in a minor degree of protection in AKR mice. This protection was associated with increased intestinal antibody titers compared to mice not demonstrating protection. These results suggest that the protective responses observed in AKR mice relative to C3H mice reflect differences in mucosal antibody responses to H.

Effect of parenteral immunization on the local immunoglobulin A response of the intestine to Shigella flexneri antigens

Most traditional methods of immunization involve parenteral vaccines. Using a chronically isolated ileal loop model as the probe, we examined the effect of a primary parenteral immunization on the local immune response of the intestine. Secretions from isolated ileal loops of rabbits given a primary parenteral immunization with Shigella flexneri without adjuvant showed a small, but definite, specific immunoglobulin A (IgA) response locally, whereas a vigorous serum antigen-specific IgG response was elicited. Also, stronger antigen-specific IgG activity was detected in secretions of parenterally immunized animals than from animals given shigella only by oral immunization. No local IgA or IgG memory response could be elicited by prior parenteral priming with S. flexneri antigens. Lastly, no increase in the primary local IgA response was found in secretions from animals given an oral dosage regimen previously shown to prime for mucosal memory and then challenged with a single parenteral dose of the same antigen. These studies demonstrate that without adjuvant, parenteral doses of S. flexneri antigens elicit both specific serum and local immune responses, but they are not able to prime for a mucosal memory response upon subsequent mucosal challenge. The implications of these findings for programs that use parenteral vaccination to protect against mucosal diseases are discussed.

Measurement of thymosin alpha 1 by disassociation microELISA

A disassociation microELISA was devised for the estimation of thymosin alpha 1, a chemically characterized thymic polypeptide isolated from bovine thymosin fraction 5. Antiserum to synthetic thymosin alpha 1 was raised in rabbits. Thymosin alpha 1 in liquid phase competed with a solid-phase-bound thymosin alpha 1 for this highly specific antibody. The method is specific, sensitive, reproducible and capable of detecting as little as 100 pg/ml of thymosin alpha 1.

Arousal of mucosal secretory immunoglobulin A antitoxin in rats immunized with Escherichia coli heat-labile enterotoxin

Specific serum and mucosal antitoxin levels were determined by enzyme-linked immunosorbent assays in rats immunized with Escherichia coli heat-labile enterotoxin (LT). Immunization by means of a parenteral prime followed by peroral boosts was the only approach that aroused titers of both serum immunoglobulin G (IgG) antitoxin and mucosal secretory IgA antitoxin that were increased fourfold or more over control values. Primary parenteral immunization was effective when given either intraperitoneally or subcutaneously with either Freund complete adjuvant or alum as the adjuvant. The magnitude of the nucosal secretory IgA antitoxin response and the degree of protection against challenge with either LT or viable LT-producing organisms were related to the number and dosage of peroral boosts. LT antigenicity, as determined by enzyme-linked immunosorbent assay, was progressively reduced by toxoiding it with increasing amounts of glutaraldehyde or a carbodiimide; when LT antigenicity was reduced by greater than 50%, the effectiveness of the toxoid in stimulating mucosal antitoxin and providing protection was compromised. Strong protection extended for more than 6 weeks only in rats immunized with a sufficient peroral dosage of LT to arouse mucosal secretory IgA antitoxin titers at least fourfold greater than those of controls. These observations indicate that the ability of LT to stimulate a mucosal secretory IgA antitoxin response is dependent on the antigenicity, route, and dosage of this immunogen; they suggest that the duration of protection in animals immunized by the peroral route is related to the extent of arousal of mucosal secretory IgA antitoxin.

Oral immunization of dogs with purified cholera toxin, crude cholera toxin, or B subunit: evidence for synergistic protection by antitoxic and antibacterial mechanisms

The immunogenicity and safety of purified cholera toxin (CT), its B subunit, and a crude culture filtrate of toxigenic Vibrio cholerae (CrT) were compared in dogs immunized orally and challenged with virulent V. cholerae. CT and CrT caused marked protection in two- or three-dose regimens. Protection due to CT occurred only with doses that caused transient, sometimes severe, diarrhea in most dogs; this protection was proportional to the peak antitoxin response in jejunal mucosa and lasted at least 15 weeks. In contrast, minimum protective doses of CrT contained much less cholera toxin, caused very mild diarrhea in only 21% of the dogs, and evoked protection that was greater than predicted from the modest jejunal antitoxin response. B subunit caused smaller jejunal antitoxin responses than did similar doses of CT and was poorly protective, the 50% protective dose being >40-fold greater than that of CT. Two observations indicated that protection due to CrT involved synergy between antibacterial and antitoxic immune responses. First, the 50% protective dose of CrT was 24-fold and >36-fold smaller than the 50% protective doses of its CT and non-CT antigenic components, respectively, when tested separately. Second, protection was greater in CrT-immunized dogs than in CT-immunized dogs for a given mucosal antitoxin response. Low doses of CrT evoked serotype-specific protection, indicating that the serotype-specific O somatic antigen contributed significatly to antibacterial protection. These results suggest that a simple, effective, nonliving oral vaccine for cholera based on combined antibacterial and antitoxic immunity can probably be achieved. However, further studies are needed to determine how a protective antitoxic response can be evoked without causing diarrhea during immunization.

In vitro synthesis of antibody to specific bacterial lipopolysaccharide by peripheral blood mononuclear cells from patients with alcoholic cirrhosis

An enzyme-linked immunosorbent assay was used to detect antibody to specific bacterial lipopolysaccharide (LPS) in serum and in pokeweed mitogen (PWM) stimulated culture supernatants of peripheral blood mononuclear cells from four patients with alcoholic cirrhosis (AC). Antibody to LPS (derived from a single strain of Escherichia coli isolated from each patient's stool), was detected in the sera of each patient to a 10(-4) dilution. Only one of four control sera was positive at the 10(-4) dilution, with the others positive at 10(-3) dilution. Antibody to LPS was detected in the culture supernatants in three of the four patients and in none of the control subjects. Supernatants from patient cultures pretreated with mitomycin C or harvested after 1 day of incubation did not have detectable antibody. These results indicate that we can expand, in vitro, the population of peripheral blood B lymphocytes obtained from patients with AC and cause them to synthesize antibody against specific LPS from their own gut flora.

Antigens of scrub typhus rickettsiae: separation by polyacrylamide gel electrophoresis and identification by enzyme-linked immunosorbent assay

Antigens of plaque-purified Rickettsia tsutsugamushi strains Gilliam, Karp, and Kato were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and were analyzed by an enzyme-linked immunosorbent assay. Six antigens were identified in each of the three prototype strains; in strain Gilliam, these antigens were located in the cell envelope fraction of the organisms. Reactivity of these isolated antigens with homologous or heterologous immune sera indicated that different macromolecules existed in all three strains, although they exhibited very similar mobilities during electrophoresis. Antigens of strain Gilliam reacted equally well with antibodies directed against Gilliam, Karp, or Kato rickettsiae. However, strains Karp and Kato each had two distinct antigens which did not react with heterologous antisera. R. tsutsugamushi antigens retained immunogenicity after electrophoresis, and antisera raised against them reacted with intact organisms and exhibited specificity in reactions with isolated antigens.

Role of antigen form in development of mucosal immunoglobin A response to Shigella flexneri Antigens

One major stumbling block in the development of an effective means to immunize against shigellosis and other enteric diseases has been the lack of a means to assess sequential mucosal immune responses to different potential immunogens. In the present study, we compared the abilities of live invasive organisms, noninvasive organisms, and nonviable antigen preparations of shigella to elicit mucosal immune responses. Whereas previous studies have found that effective immunity was produced best by vaccination with live invasive strains of shigella, in the present study, live noninvasive strains that did not produce any histopathological damage were consistently able to produce local (immunoglobulin A) immune responses as vigorous as those of the invasive strains. Further, acetone-killed shigella antigen was also an effective mucosal immunogen, whereas hot phenol-water-extracted shigella lipopolysaccharide was ineffective, possibly due to the method of preparation. A single oral or parenteral priming was ineffective in enhancing the mucosal immune response when restimulated 1 month later with the same antigen. However, a mucosal memory response was found to be present several months after a triple mucosal stimulation with a locally invasive vaccine strain.

No impairment of local intestinal immune response to keyhole limpet haemocyanin in the absence of Peyer's patches

The role of Peyer's patches in the local intestinal and serum antibody responses to keyhole limpet haemocyanin (KLH) was studied in rabbits with chronically isolated ileal loops. Four weekly doses of 400 microgram KLH were administered into loops prepared with and without Peyer's patches. Isotype-specific IgA and IgG anti-KLH in loop secretions collected twice each week and in sera collected weekly were assessed by enzyme-linked immunosorbent assay. Fluid IgA anti-KLH in loops without Peyer's patches first showed a statistically significant increase on day 25, 1 week later than control loops with Peyer's patches. However, some animals in the group without Peyer's patches showed a rise as early as day 7, and the differences from controls were not statistically significant at any time. No statistically significant rise in fluid or serum IgG anti-KLH occurred in either group. Thus, Peyer's patches were not essential for local intestinal antibody response to KLH, a soluble macromolecular antigen. The findings suggest that the innumerable small lymphoid nodules in the gastrointestinal tract, or other mechanisms of antigen processing, play an important role in local intestinal immune responses.

Respective contributions to protection of primary and booster immunization with Escherichia coli heat-labile enterotoxin in rats

The respective contributions to protection of the route and dosage of primary and booster immunizations with Escherichia coli heat-labile enterotoxin were evaluated in rats. The degree of protection was determined by challenge with toxin and viable bacteria in ligated ileal loops, and the serum antitoxin response was assayed by enzyme-linked immunosorbent assay. Primary immunization was effective only when given by the parenteral route. The degree of protection was enhanced a fivefold dosage increase in the primary parenteral immunization in rats given constant dosages of booster immunizations either parenterally or perorally, but not by further dosage increases. In contrast, the degree of protection rose when dosages of the booster immunizations were increased over a 25-fold range. Four weekly peroral, but only two biweekly parenteral, booster immunizations were necessary to achieve strong protection; biweekly combined parenteral and peroral booster immunizations yielded both strong, immediate and extended protection. The degree of protection against the toxin correlated with that against viable bacteria and with elevated serum antitoxin titers: all seven groups with a protection index of greater than 5 against the toxin had strong protection against heat-labile toxin-producing strains and fourfold or greater increases in the antitoxin titers, whereas none of the nine groups with a protection index of less than 3 was protected against bacteria or had an equivalent antitoxin response. These observations show that once an adequate parenteral primary immunization is given, the degree of protection is influenced primarily by the dosage of the booster immunizations, the necessary number of which is dependent on their route of administration.

Immune response of the ileum to invasive Escherichia coli diarrheal disease in rabbits

We have previously characterized a rabbit model of invasive Escherichia coli diarrhea. The purpose of this study was to measure the in vitro synthesis of immunoglobulin and anti-invasive E. coli antibody by ileal tissue and levels of anti-invasive E. coli antibody in sera and ileal contents at intervals after diarrhea. Immunoglobulin synthesis by the ileum peaked at 7 to 9 days, but returned to normal by 11 to 13 days post-diarrhea.l Secretory immunoglobulin A (IgA) was synthesized in greater quantity than was IgG or IgM. Anti-invasive E. coli antibody synthesis peaked at 11 to 13 days, decreased to less than half of maximum by 21 to 24 days, but was increased again at 30 to 33 days post-diarrhea. Secretory IgA anti-invasive E. coli antibody was synthesized in greater quantity than was IgG or IgM antibody. Specific antibody of the IgG and IgM classes, but not of the IgA class, appeared in sera by 4 to 6 days and peaked at 7 to 15 days post-diarrhea. Secretory IgA anti-invasive E. coli antibody was detected in ileal contents by 7 to 13 days, but maximum levels were not reached until 50 to 55 days post-diarrhea. IgG and IgM anti-invasive E. coli antibodies were not detected in ileal contents. The synthesis and secretion of secretory IgA antibody were major components of the immune response of the ileum after infection with an invasive bacterium.

Variables affecting local immune response in ileal loops: role of immunization schedule, bacterial flora, and postsurgical inflammation

Several variables inherent in chronically isolated ileal (Thiry-Vella) loops in rabbits were studied for their effect on the local immune response of the intestine to live, locally invasive bacteria (Shigella X16). A much more vigorous local immunoglobulin A response to Shigella X16 was elicited when rabbits were immunized in their Thiry-Vella loops shortly after surgical creation of the loop than if a week were allowed to pass before they were immunized. Three major differences existed in Thiry-Vella loops on the day after surgery and a week later: (i) their microbial flora, (ii) nonspecific acute inflammation due to the surgery itself, and (iii) the histological appearance of the intestine. On day 1 after surgical creation of the Thiry-Vella loop, there were few bacteria in the loop, and the histology was that of normal small bowel except for mild acute inflammation due to the surgery. By day 6 after surgery, all loops contained large numbers of Pseudomonas aeruginosa and other aerobes, an atrophy of intestinal epithelium occurred, and the acute inflammation due to surgical trauma had subsided. By artificially colonizing Thiry-Vella loops with 10(8) or 10(10) live P. aeruginosa on the day of surgery, we found that the presence of these bacteria alone did not greatly diminish local immune responses to live Shigella. Furthermore, when the acute inflammation due to surgical trauma was recreated in loops 6 days old, no enhancement of the immune response was seen as compared to nontraumatized 6-day-old Thiry-Vella loops. The difference between immunization soon after surgery and a week later related to changes that occur in the loop itself with increased isolation. Finally, multiple immunizations of Thiry-Vella loops resulted in a more vigorous local immunoglobulin A response than a single immunization. These studies demonstrated that Thiry-Vella loop models can be useful in studying the kinetics of local immune responses by the intestine only if careful attention is paid to key variables inherent in the Thiry-Vella loop models themselves.

Enhancement by cholera toxin of IgA secretion from intestinal crypt epithelium

Studies of the effects of cholera toxin on the intestine have produced conflicting results regarding stimulation of IgA secretion. In the present study rabbit ileal loops were perfused with saline, and the IgA content of the perfusate was assessed by immunoradiometric assay. Crypt epithelial IgA content in biopsies was studied by immunofluorescence. Cumulative loop fluid IgA production 300 minutes after exposure to cholera toxin was 6216 +/- 993 microgram/cm compared with 4646 +/- 953 microgram/cm in controls (P < 0 . 20). However, rate of fluid IgA production above baseline at 300 minutes was 1742 +/- 181 microgram/h/cm in cholera loops and 1049 +/- 310 microgram/h/cm in controls, and the mean difference between the cholera and control loops was statistically significant (P < 0 . 05). In biopsies, mean rank of crypt epithelial IgA at 300 minutes was decreased compared with controls (P < 0 . 05). The findings of increased rate of fluid IgA production and decreased epithelial IgA suggest that a single dose of cholera toxin enhanced secretion of IgA from crypt epithelium into the intestinal lumen, although the magnitude of the enhancement was not great.

Antitoxic immunity to cholera in dogs immunized orally with cholera toxin

Colera toxin was evaluated as an oral immunogen against experimental canine cholera. Dogs were immunized orally with 100-microgram doses of purified cholera toxin or comparable doses of crude toxin. Both doses caused moderate diarrhea in most nonimmune dogs. Repeated oral doses (12 doses in 54 days) gave marked protection against the diarrheal effect of oral toxin, provoked a vigorous antitoxic response in jejunal mucosa, and gave nearly complete protection against subsequent oral challenge with living virulent Vibrio cholerae. Protection appeared to be due largely to the antitoxic response in intestinal mucosa. The effectiveness of cholera toxin as an oral vaccine contrasts with the previously described ineffectiveness of toxoid given orally. This study provides an example of mucosal immunity due to a nonreplicating vaccine given orally and suggests that cholera toxin may be useful as a component of an oral vaccine for cholera.

Suppression of local intestinal immunoglobulin A immune response to cholera toxin by subcutaneous administration of cholera toxoids

Cholera toxin has been shown to modulate immune responses, generally producing enhancement when administered simultaneously with antigen and suppression when administered a day or more earlier. In a previous study using chronically isolated ileal loops in rabbits, we found that two subcutaneous (s.c.) "priming" and "boosting" doses of biologically active cholera toxin suppressed the local intestinal immunoglobulin A response to intraloop doses of cholera toxin. In the study reported here, two different biologically inactive but antigenically intact cholera toxoids, glutaraldehyde toxoid and choleragenoid, where administered s.c. by the same immunization schedule as for toxin in the earlier experiment. Suppression of local immune response to intraloop cholera toxin as compared with animals receiving no s.c. inoculations was again found. The results suggest that in this model suppression was immunological (mediated by an immunological mechanism) rather than toxigenic (mediated by biological activity of cholera toxin). In addition, the occurrence of suppression of local intestinal immune response after systemic immunization suggests that suboptimal protection against enteric infections could occur after s.c. vaccination.

Enzyme-linked immunosorbent assay for immunoglobulin G and immunoglobulin A antibodies to Shigella flexneri antigens

An enzyme-linked immunosorbent assay has been developed to detect class-specific antibodies to Shigella flexneri lipopolysaccharide antigens. This enzyme-linked immunosorbent assay system has been used to measure antibodies present in serum or intestinal secretions without further purification. It is considerably more sensitive than passive hemagglutination, allowing detection of as little as 1.3 ng of specific immunoglobulin G antibody per ml in immune sera. Optimal conditions for this assay are outlined in this report.