The demonstration and function of antibodies in the gastrointestinal tract

Protective Immunity Against Enterotoxigenic Escherichia coli by Oral Vaccination of Engineered Lactococcus lactis

Enterotoxigenic Escherichia coli (ETEC) is one of the leading causes of diarrhea in children globally, and thus suitable vaccines are desired. Antigen display on lactic acid bacteria is a reliable approach for efficient oral vaccination and preventing bowel diseases. To develop an oral vaccine against ETEC, the gene of the binding domain from heat-labile toxin (LTB), a key ETEC virulence factor, was codon-optimized and cloned into a construct containing a signal peptide and an anchor for display on L. lactis. Bioinformatics analysis showed a codon adaptation index of 0.95 for the codon-optimized gene. Cell surface expression of LTB was confirmed by transmission electron microscopy and blotting. White New Zealand rabbits were immunized per os (PO) with the recombinant L. lactis, and the antibody titers were assayed with ELISA. In vitro neutralization assay was performed using mouse adrenal tumor cells and rabbit ileal loop test was performed as the in vivo assay. ELISA results indicated that oral administration of the engineered L. lactis elicited a significant production of IgA in the intestine. In vitro neutralization assay showed that the effect of the toxin could be neutralized with 500 µg/ml of IgG isolated from the oral vaccine group. Furthermore, the dose of ETEC causing fluid accumulation in the ileal loop test showed a tenfold increase in rabbits immunized with either recombinant L. lactis or LTB protein compared to other groups. Our results imply that recombinant L. lactis could potentially be an effective live oral vaccine against ETEC toxicity.

A Novel, Orally Delivered Antibody Therapy and Its Potential to Prevent Clostridioides difficile Infection in Pre-clinical Models

Clostridioides difficile infection (CDI) is a toxin-mediated infection in the gut and a major burden on healthcare facilities worldwide. We rationalized that it would be beneficial to design an antibody therapy that is delivered to, and is active at the site of toxin production, rather than neutralizing the circulating and luminal toxins after significant damage of the layers of the intestines has occurred. Here we describe a highly potent therapeutic, OraCAb, with high antibody titers and a formulation that protects the antibodies from digestion/inactivation in the gastrointestinal tract. The potential of OraCAb to prevent CDI in an in vivo hamster model and an in vitro human colon model was assessed. In the hamster model we optimized the ratio of the antibodies against each of the toxins produced by C. difficile (Toxins A and B). The concentration of immunoglobulins that is effective in a hamster model of CDI was determined. A highly significant difference in animal survival for those given an optimized OraCAb formulation versus an untreated control group was observed. This is the first study testing the effect of oral antibodies for treatment of CDI in an in vitro gut model seeded with a human fecal inoculum. Treatment with OraCAb successfully neutralized toxin production and did not interfere with the colonic microbiota in this model. Also, treatment with a combination of vancomycin and OraCAb prevented simulated CDI recurrence, unlike vancomycin therapy alone. These data demonstrate the efficacy of OraCAb formulation for the treatment of CDI in pre-clinical models.

Digestion dynamics in broilers fed rapeseed meal

Rapeseed proteins are described to be poorly digestible in chickens. To further identify some molecular locks that may limit their use in poultry nutrition, we conducted a proteomic study on the various chicken digestive contents and proposed an integrative view of the proteins recruited in the crop, proventriculus/gizzard, duodenum, jejunum, and ileum for digestion of rapeseed by-products. Twenty-seven distinct rapeseed proteins were identified in the hydrosoluble fraction of the feed prior ingestion. The number of rapeseed proteins identified in digestive contents decreases throughout the digestion process while some are progressively solubilized in the most distal digestive segment, likely due to a combined effect of pH and activity of specific hydrolytic enzymes. Fifteen chicken proteins were identified in the hydrosoluble proventriculus/gizzard content, including chymotrypsin-like elastase and pepsin. Interestingly, on the 69 distinct proteins identified in duodenum, only 9 were proteolytic enzymes, whereas the others were associated with homeostasis, and carbohydrate, lipid, vitamin and hormone metabolisms. In contrast, chicken proteins identified in jejunal and ileal contents were mostly proteases and peptidases. The present work highlights the relevance of using integrative proteomics applied to the entire digestive tract to better appreciate the protein profile and functions of each digestive segment.

Vaccines against enteric infections for the developing world

Since the first licensure of the Sabin oral polio vaccine more than 50 years ago, only eight enteric vaccines have been licensed for four disease indications, and all are given orally. While mucosal vaccines offer programmatically attractive tools for facilitating vaccine deployment, their development remains hampered by several factors: -limited knowledge regarding the properties of the gut immune system during early life; -lack of mucosal adjuvants, limiting mucosal vaccine development to live-attenuated or killed whole virus and bacterial vaccines; -lack of correlates/surrogates of mucosal immune protection; and -limited knowledge of the factors contributing to oral vaccine underperformance in children from developing countries. There are now reasons to believe that the development of safe and effective mucosal adjuvants and of programmatically sound intervention strategies could enhance the efficacy of current and next-generation enteric vaccines, especially in lesser developed countries which are often co-endemic for enteric infections and malnutrition. These vaccines must be safe and affordable for the world's poorest, confer long-term protection and herd immunity, and must be able to contain epidemics.

Effects of sample processing on the measurement of specific intestinal IgA immune responses

The effects of techniques commonly used in the collection and processing of human intestinal fluid on the specific secretory immunoglobulin A (sIgA) response following oral immunization with the live typhoid vaccine Salmonella typhi Ty21a were examined. It was observed that the failure to adjust specific intestinal anti-typhoid lipopolysaccharide IgA antibody titres for total secretory IgA resulted in a false-negative detection rate of 19.8% and a false-positive detection rate of 7.4%. Furthermore, these specific responses were significantly diminished if the intestinal fluid was subjected to heat inactivation to reduce intestinal protease activity (p = 0.0083), but were not affected if stored at -70 degrees C for up to 1 year, without heat inactivation. It was concluded that in the processing of the intestinal fluid samples for specific sIgA determination heat inactivation significantly reduced specific sIgA titres, and that the failure to adjust absolute titres for total sIgA content resulted in a significant false-negative detection rate.

Small intestinal bacterial overgrowth in patients with chronic lymphocytic leukaemia

As part of a study to assess the possible contribution of lymphoid infiltration of the gastrointestinal mucosa to occult blood loss or malabsorption 20 patients with chronic lymphocytic leukaemia (CLL) had a lactulose hydrogen breath test. In 10 cases (50%) a small intestinal peak was detected, suggesting small bowel bacterial overgrowth, and this was confirmed in seven patients by the positive culture of jejunal aspirate. Of the patients with a positive hydrogen breath test, radiological examination showed a duodenal diverticulum in two but no anatomical abnormalities in the other cases. There was no evidence of achlorhydria and transit times were normal. There was no difference in the incidence of hypogammaglobulinaemia among those patients with evidence of small intestinal bacterial overgrowth and those without. Seven patients with a positive hydrogen breath test, however, had undetectable secretory piece in their jejunal aspirates whereas this was present in all patients with a normal breath test who had local immunoglobulin concentrations measured (p less than 0.05), indicating that the small intestinal bacterial overgrowth may be due to impaired local immunity.

Sensitization to epithelial antigens in chronic mucosal inflammatory disease. III. Serum factor modulates circulating and mucosal mononuclear-cell reactivity to epithelial cell-associated components of colon (ECAC-C)

A prior report indicated that sera together with peripheral blood mononuclear cells from patients with Crohn's disease were reactive with epithelial cell-associated components derived from small bowel (ECAC-SB). In the present study, we sought to determine whether similar components (designated ECAC-C) from everted, inflated loops of murine colon could be purified to homogeneity in aqueous soluble form and physiochemically characterized; if sera and/or peripheral mononuclear cells from patients with a chronic idiopathic inflammatory disorder of intestinal mucosa were specifically reactive with ECAC-C; whether immunoglobulin was the factor conferring specificity to the anti-ECAC-C response; and if this immunoglobulin was actively synthesized by human lamina propria B lymphocytes isolated from disease-involved intestinal mucosa. Preparative polyacrylamide gel electrophoresis followed by elution of specific bands resulted in the isolation of three major proteins in homogeneous form. Each was a distinctive macromolecule by molecular weight (39,000, 63,000, 148,000), carbohydrate/protein content, and serologically detectable determinants as assessed by quantitative hemagglutination inhibition. By a 51Cr release microcytotoxicity assay, ECAC-C-labeled indicator cells were specifically lysed by sera and peripheral blood mononuclear cells from patients with ulcerative colitis (8.0 +/- 6.8%) and Crohn's disease (13.2 +/- 4.7%), compared with age-/sex-matched controls (0.6 +/- 0.9 and 0.2 +/- 0.4%, respectively). That the factor conferring ECAC-C specificity was immunoglobulin was demonstrated by the retention of ECAC-C-specific reactivity of patient sera in the presence of normal peripheral blood mononuclear cells, the ability of patient sera (without cells) to effect complement-mediated lysis against erythrocytes labeled with ECAC-C (8.0 +/- 6.7%) but not with control kidney antigen (0.7 +/- 0.7%), and the fact that purified immunoglobulin from patient sera could substitute for the latter in an ECAC-C-specific antibody-dependent cellular cytotoxicity assay. Unique aspects of this ECAC-C reactivity included its absence from sera in other disorders with a known or presumed autoimmune basis (systemic lupus erythematosus, chronic active hepatitis) and the lack of simultaneous reactivity directed toward control antigens, isolated from kidney in a manner analogous to that used for ECAC-C. The importance of ECAC-C-specific immune responses at the mucosal level was also examined using mononuclear cells isolated from disease and control intestinal lamina propria (LPMC).(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of monocytes by portal serum and its relationship to immunoglobulin, immune complex and endotoxin content

To investigate the possibility that a "spillover effect" of substances from the portal vein into the systemic circulation accounts for the abnormal monocyte function in patients with liver disease, we have incubated human peripheral blood monocytes with paired specimens of portal and systemic serum from humans and rabbits. Monocytes incubated with portal serum released more of a lysosomal enzyme, N-acetyl-B-glucosaminidase, than those incubated with systemic serum (p less than 0.05). In order to delineate the factors responsible for this increased activity, the content of immune complexes, immunoglobulins and endotoxin in the paired specimens of portal and systemic serum was measured. Endotoxin was found in none of 16 human specimens of portal blood and five of the 16 rabbit specimens. Modestly increased levels of immune complexes, particularly of the IgG class, were found in the portal serum compared to the systemic serum (p less than 0.01). Corresponding studies on immunoglobulins showed a higher concentration of IgA in portal serum (p less than 0.05), but no difference in other classes of immunoglobulins or complement levels. There was good correlation between the enzyme production by monocytes and the concentration of immune complexes, particularly IgA (r = 0.687, p less than 0.001), but there was no relationship to the presence or absence of endotoxin. This evidence suggests that portal serum contains substances, particularly immune complexes, which under normal circumstances are sequestered by the liver. These are capable of "activating" monocytes in vitro and may play a role in the pathogenesis of certain types of liver disease.

Measurement of immunoglobulin A, G, and M class rotavirus antibodies in serum and mucosal secretions

A solid-phase, enzyme-linked immunospecific assay for measurement of different immunoglobulin classes of human rotavirus antibodies is described. The antigen, which was adsorbed directly to polyvinyl microtiter plates, consisted of a clarified cell culture stock of the simian rotavirus SA 11. The assay was sensitive and reproducible and could readily be calibrated to determine concentrations of each class of antibody. The assay was applied to measurements of rotavirus antibodies in serum, colostrum, milk, and fecal samples. It particularly facilitates investigations of the role of immunoglobulin A antibodies in immunity to rotavirus infections.

Measurement of intestinal antibody by radioimmunoassay

The study of antibody responses in the intestine has been greatly hampered by lack of reproducible sensitive assays. An assay for measuring antibody against bacteria capable of regularly detecting gut antibody in gastroenteritis is described. It is based on absorption of antibody onto bacteria and measurement of the amount of antibody bound using radiolabelled anti-immunoglobulin antibody. Anti-light chain antibody is used to detect all classes of antibody as well as partially degraded antibody which retains the capacity to bind; anti-alpha and anti-gamma antibody is used to measure IgA and IgG antibody. The sensitivity of the assay depends on the use of anti-immunoglobulin antibody purified by affinity chromatography and allows measurement of nanogram amounts of antibody. Its specificity and kinetics are described and the particular advantages it provides in the measurement of antibacterial antibody in the intestine are discussed.

IgE levels in intestinal juice

This investigation was performed to determine the possible significance of the IgE levels in intestinal secretions for the recognition of type I food allergy (immediate hypersensitivity). Four groups of individuals were studied and compared with each other: (1) healthy controls and patients with gastrointestinal disorders not affecting the small intestine; (2) patients with small intestinal disease; (3) patients with various manifestations of allergy but without food intolerance; and (4) patients with atopic sensitivity to foods. Despite the presence of proteolysis in the intestinal fluid, a statistically highly significant increase of the intestinal IgE level was observed in patients of group 4 with type I food allergy and in patients of group 3 as compared with normals. This was associated with an increase in the serum IgE level. An increased synthesis of the IgE in the lamina propria of the small intestine is most probable, but not yet adequately established.

Antibody response of the lactating sow to oral immunization with Escherichia coli

Oral immunization of the lactating sow with live Escherichia coli (O8:K88) stimulated an IgA anti-K88 antibody response in mammary secretions and significantly enhanced the capacity of whey to inhibit adhesion of the inoculum E. coli strain to isolate pig enterocytes. An increase in agglutinating anti-O8 activity was also evident in jilk and was associated with both the IgA and IgM immunoglobulin classes. These results are consistent with the concept of a gut-mammary link, although measurement of specific antibody in the intestinal secretions of these animals suggested that there may be a difference in response duration at the two secretory sites. Prolonged oral administration of heat-killed organisms also stimulated specific antibody synthesis within the mammary gland, although the response, particularly to the O antigen, was both reduced and delayed in its appearance.

Increase in the population of duodenal immunoglobulin A plasmocytes in axenic mice associated with different living or dead bacterial strains of intestinal origin

Various bacterial strains were tested for their ability to stimulate immunoglobulin A (IgA) plasmocytes to populate the duodenal lamina propria in axenic mice. The mice were associated with the strains for at least 4 weeks. The strains inhabiting the conventional mouse intestine and belonging to the genera Lactobacillus, Streptococcus, Eubacterium, Actinobacillus, Micrococcus, Corynebacterium, and Clostridium (including the extremely oxygen-sensitive ones) are only slightly or nonimmunogenic, whereas the strains belonging to the genera Bacteroides and Escherichia have an immunogenic effect. The same result was obtained with Bacteroides and Escherichia strains isolated from the digestive tract of other animal species. The kinetics of appearance of intestinal IgA plasmocytes are similar in axenic mice monoassociated with a stimulatory strain and in conventional mice. The association of two or more strains with axenic mice leads either to the same or a greater number of duodenal IgA plasmocytes as that obtained with the most stimulatory strain monoassociated with axenic mice. The maximum stimulation recorded in all of these trials represents about two-thirds of that observed in conventional mice and was obtained in the duodenum of gnotoxenic mice harboring four bacterial strains isolated from the conventional mouse microflora. The orally administered killed cells of two immunogenic strains, E. coli and Bacteroides sp., are as immunogenic as the living cells, provided that their concentration in the digestive tract is sufficient.

Analysis of the lympho-plasmacytic infiltrate in Crohn's disease with special reference to identification of lymphocyte-subpopulations

Lympho-plasmacytic infiltrates in cryostat sections (resected small intestine or colon specimens and rectal biopsies) from 29 patients with Crohn's disease (CD) were studied with the immunoperoxidase and immunofluorescence technique, by means of specific anti-human lymphocyte globulin (ALG) and specific anti-human T-lymphocyte globulin (ATG). Control specimens were obtained from 16 patients with ulcerative colitis (UC) and 12 subjects without inflammatory bowel disease. Characteristic transmural inflammatory infiltrates in CD consisted mainly of lymphocytes. A wide variation of the relative T-cell proportion was observed. However, in contrast with UC, abundant numbers of T-lymphocytes in CD were often detected, particularly in the deeper layers of the bowel wall. Furthermore, in serial sections immunoglobulin-containing plasma cells were counted, using specific anti-IgA, -IgM, and -IgG antisera. A significant reduction of the IgA/IgM plasma cell-ratio was found in CD in comparison with UC and controls. Our results indicate that in CD a chronic cellular immune reaction is going on within the diseases gut, involving increased numbers of lymphocytes and particularly T-cells. It remains to be established whether a deficient IgA barrier has to be considered of primary pathogenetic importance.

Intestinal lesions in immune deficiency

The descriptive studies of intestinal lesions in immune deficiency and the research that has been done in order to explain their pathogenesis are reviewed. Current knowledge in this field is inadequate, and some of the intriguing phenomena described defy reasonable explanation, including the special role of Giardia lamblia and the rarity of gastrointestinal lesions in isolated IgA deficiency. Several hypotheses have been proposed regarding these phenomena.

Human faecal immunoglobulins in healthy infants and children, and in some with diseases affecting the intestinal tract or the immune system

IgA, IgG and IgM is faeces were quantified by single radial immunodiffusion using extracts of freeze-dried faeces. IgA in small specimens of faeces seemed to mirror the total amound of IgA secreted into the gut at the time of sampling. Presumptive normal values of faecal IgA concentrations in infants and children were established. Agglutinins to rabbit erythrocytes served as markers for the antibody activity. Infants and children just recovered from enteritis of probably infectious origin had higher concentrations of both IgA and agglutinins in faeces. Faeces from three out of five patients with ulcerative colitis in remission, contained IgG in markedly increased concentrations. Two patients with IgA deficiency had no detectable IgA in faeces, but had increased levels of faecal IgM which also agglutinated rabbit erythrocytes. Immunoglobulins were not demonstrated in faeces from three patients with agammaglobulinaemia. The findings indicate that faeces can be used for assay of immunoglobulins of the intestinal tract.

Breast feeding and biological properties of faecal E. coli strains

Human milk may contribute to protection against gram-negative infection by promoting intraluminal agglutination or killing of bacteria or by preventing bacterial attachment to epithelial surfaces. This paper explores the effect of human milk on the sensitivity of faecal E. coli to serum bactericidal activity and agglutination specificity, factors which have been regarded as related to virulence. Faecal E. coli isolated from breast-fed infants differed from those from formula-fed infants in two respects: They were more sensitive to the bactericidal effect of human serum and more often spontaneously agglutinating. E. coli strains isolated from sources outside the gastro-intestinal tract, that is the prepuce and female peri-urethral region, were in breast-fed babies less sensitive than faecal strains. The findings are compatible with the hypothesis that a breast-milk factor favours the proliferation of mutant strains. The observed effects of breast-milk might be associated with decreased bacterial virulence, and be one of the ways in which breast-feeding protects against infection.

Adsorption in vitro to Escherichia coli of antibodies and other proteins in bovine serum and colostrum and its effects on the production of E. coli agglutinins

IgGl, IgG2, IgA and IgM from bovine serum and colostrum are adsorbed by Escherichia coli in vitro; lactoferrin is also adsorbed from colostrum and alpha2 macroglobulin from serum. The colostral adsorbed proteins on E. coli appear to reduce formation of agglutinins when the treated bacteria are injected into rabbits and guinea-pigs. Assay of the concentration of proteins dissociated from colostrum-treated cells showed equal amounts of secretory IgA AND IgGl, half that amount of IgG2, and traces of IgM and lactoferrin. Dissociation of proteins from serum-treated E. coli yielded equal amounts of IgGl and IgG2, traces of IgA and an alpha2 macroglobulin, but no IgM.

Dog immunoglobulins. I. immunochemical characterization of dog serum, parotid saliva, colostrum, milk and small bowel fluid

The levels of immunoglobulins A, M and G were measured in dog serum, colostrum, milk, parotid saliva and small bowel fluid using the single radial immunodiffusion method. All the external secretions except early colostrum, by contrast with serum, were found to be rich in IgA with small quantities of IgM and IgG. Exocrine immunoglobulins were partially characterized by gel filtration.

Immunoglobulin characterization of human pancreatic fluid

Human pancreatic fluid obtained from 2 subjects, each with a traumatic pancreatic fistula, contained detectable levels of IgG, IgA, IgM, IdD, and IgE. Although the mean IgG/IgA ratio for 10 random specimens was 1.63, the relative concentration was estimated to be less than unity when extreme values were eliminated. The molecular weight of IgA in pancreatic fluid was found to be comparable to that of the IgA molecule in serum. The absence of secretory component in pancreatic IgA provides further evidence that pancreatic IgA and serum IgA are similar. Serial determinations of the immunoglobulins stored at 4 degrees C showed a progressive decrease of all immunoglobulins, the order of stability being IgG approximately equal to IgA larger than IgM approximately equal to IgD. The demonstrated proteolytic activity in the specimens could account for the immunoglobulin decay and for the variable detection of IgM and IgD in pancreatic-fluid specimens.

Immunoglobulin synthesis and antibody content in the small intestine of the rabbit

The concentration of immunoglobulin and specific antibody in the serum and the intestinal fluid and the rate of synthesis of immunoglobulin in the small intestine was measured in normal and immunized rabbits. IgA was found to be the predominant immunoglobulin in the intestinal fluid. IgA and IgG were secreted at rates of 4-3 mug/cm/hr and 1-3 mug/cm/hr respectively. Specific anti-Vibrio cholerae antibodies in the intestine were found mainly in the IgA class after oral immunization.

Inhibition of Escherichia coli by bovine colostrum and post-colostral milk. I. Complement-mediated bactericidal activity of antibodies to a serum susceptible strain of E. coli of the serotype O 111

Bovine colostral whey diulted in unheated bovine milk or in Kolmer saline containing 5 per cent pre-colostral calf serum was bactericidal for Escherichia coli NCTC 9703 (serotype O 111). Whey diluted in saline without pre-colostral calf serum was inactive. Bactericidal activity was abolished by heating at 56 degrees for 30 minutes or by pre-incubating with N-acetyl-L-tyrosine ethylester, indicating that complement present in milk or pre-colostral calf serum was involved in the bactericidal activity. Undiluted colostral whey was inactive even in the presence of up to 20 per cent pre-colostral calf serum, probably due to a prozone effect. Milk heated at 80 degrees for 10 minutes was also shown to have a limited anti-complementary effect. Post-colostral milk from some cows had bactericidal activity, whereas similar milks from other cows were either inactive or active only after addition of pre-colostral calf serum, indicating that antibodies to E. coli or complement or both may or may not be present in the post-colostral milk of different cows. The implications of these findings in relation to the bacterial flora of the intestinal tract of neonates are discussed.

Appearance of specific colostrum antibodies after clinical infection with Salmonella typhimurium

Colostrum and serum antibodies to Salmonella typhimurium have been found in three patients after clinical gastrointestinal infection during pregnancy. High levels of colostrum IgA agglutinins were directed specifically against both the flagellar and somatic antigens of the infective organism. The levels of colostrum agglutinating activity exceeded those found in the patients sera, while control colostrum gave negative results.