Histomorphometric evaluation of intestinal cellular immune responses in pigs immunized with live oral F4ac+ non-enterotoxigenic E. coli vaccine against postweaning colibacillosis

Evidence-Based Approaches for Determining Effective Target Antigens to Develop Vaccines against Post-Weaning Diarrhea Caused by Enterotoxigenic Escherichia coli in Pigs: A Systematic Review and Network Meta-Analysis

Simple Summary

Owing to the levels of mortality and morbidity associated with enterotoxigenic Escherichia coli (ETEC) inflicted diarrhea, as well as the scope of the global disease burden, several initiatives to develop effective vaccines have been launched. We conducted a meta-analysis to assess the efficacy of commercially available and candidate vaccines against ETEC-associated post-weaning diarrhea in pigs. The effectiveness of vaccines was evaluated using three clinical outcomes: mortality, diarrhea, and average daily weight gain. Subsequently, a simultaneous comparison of vaccines was conducted using a Bayesian network meta-analysis approach to generate evidence-based data on the most effective vaccine based on their target antigens. The results indicated that vaccinated pigs had a significantly lower risk of diarrhea and mortality when compared to non-vaccinated pigs. Furthermore, the findings also showed that a multivalent vaccine that targets both fimbriae and enterotoxins should be prioritized to combat post-weaning diarrhea in pigs.

Abstract

In this study, we conducted a meta-analysis (MA) and systematic review to evaluate the effectiveness of vaccines against post-weaning diarrhea (PWD), caused by enterotoxigenic Escherichia coli (ETEC), in piglets. A Bayesian network meta-analysis (NMA) was also performed to compare the effects of combining different target antigens on vaccine efficacy. Relevant electronic databases were searched using pre-specified search terms, and 17 studies were selected based on three outcomes: diarrhea, mortality, and average daily weight gain (ADWG). In pairwise MA, the vaccinated group showed a significant decrease in diarrhea (OR = 0.124 [0.056, 0.275]) and mortality (OR = 0.273 [0.165, 0.451]), and a significant increase in ADWG (SMD = 0.699 [0.107, 1.290]) compared with those in controls. Furthermore, NMA results showed that all vaccine groups, except for group D (LT enterotoxin), were effective against PWD. Rank probabilities indicated that the F4 + F18 + LT combination was the best regimen for preventing diarrhea (SUCRA score = 0.92) and mortality (SUCRA score = 0.89). NMA also demonstrated that, among the vaccine groups, those inducing simultaneous anti-adhesion and antitoxin immunity had the highest efficacy. Our results provide evidence-based information on the efficacy of vaccines in reducing PWD incidence in pigs and may serve as guidelines for antigen selection for commercial vaccine development in the future.

Antigen Delivery System II

This chapter reviews papers mostly written since 2005 that report results using live attenuated bacterial vectors to deliver after administration through mucosal surfaces, protective antigens, and DNA vaccines, encoding protective antigens to induce immune responses and/or protective immunity to pathogens that colonize on or invade through mucosal surfaces. Papers that report use of such vaccine vector systems for parenteral vaccination or to deal with nonmucosal pathogens or do not address induction of mucosal antibody and/or cellular immune responses are not reviewed.

Levamisole stimulates proliferation of circulating and intestinal immune cell subsets, gut health and performance in weaned pigs

Valpotić, H., Šperanda, M., Kovšca-Janjatović, A., Ðidara, M., Lacković, G., Božić, F., Habrun, B., Srečec, S., Mataušić-Pišl, M. and Valpotić, I. 2014. Levamisole stimulates proliferation of circulating and intestinal immune cell subsets, gut health and performance in weaned pigs. Can. J. Anim. Sci. 94: 43–53. With the growing knowledge of the porcine immune system and its endogenous modulation, it has been clearly stated that exogenous modulation through the use of substances able to modulate immune functions represents an important prophylactic/therapeutic approach in prevention/treatment of both stress- and F4+ and F18+ enterotoxigenic E. coli (ETEC)-induced infections accompanied weaning. The aim of this study was to evaluate the effectiveness of levamisole (LEVA; 2.5 mg kg−1 BW in 10 mL) applied per os to weaned pigs in proliferation of circulating and intestinal immune cell subsets throughout a period of 5 wk. Changes in proportion or number of peripheral blood and ileal mucosal leukocytes tested were studied either weekly by flow cytometry or at the end of the experiment (day 35) by immunohistology/histomorphometry, respectively. Pigs treated with LEVA had increased proportions of peripheral blood CD45+ lymphoid cells, CD4+ and CD8+ T cells, and CD21+ B cells (P<0.01) between days 14 and 35 following the treatment. Also, LEVA stimulated the proliferation of CD45RA+ naïve lymphoid cells in interfollicular (P<0.001) and follicular areas (P<0.05) of ileal Peyer’s patches at day 35 of the experiment. These pigs had a significantly higher (P<0.05) average body weight (19.7 vs. 17.1 kg) and weight gain at the end of experiment compared with the control pigs (for 15%). We conclude that LEVA stimulated the proliferation of circulating and intestinal lymphoid cell subsets tested and improved performance in weaned pigs, and thus, the drug may nonspecifically enhance their immunity/resistance to F4+ and F18+ ETEC strains.

On the future contents of a small journal of histochemistry

In the last three years, more than 70,000 scientific articles have been published in peer reviewed journals on the application of histochemistry in the biomedical field: most of them did not appear in strictly histochemical journals, but in others dealing with cell and molecular biology, medicine or biotechnology. This proves that histochemistry is still an active and innovative discipline with relevance in basic and applied biological research, but also demonstrates that especially the small histochemical journals should likely reconsider their scopes and strategies to preserve their authorship. A review of the last three years volumes of the European Journal of Histochemistry, taken as an example of a long-time established small journal, confirmed that the published articles were widely heterogeneous in their topics and experimental models, as in this journal's tradition. This strongly suggests that a journal of histochemistry should keep its role as a forum open to an audience as broad as possible, publishing papers on cell and tissue biology in a wide variety of models. This will improve knowledge of the basic mechanisms of development and differentiation, while helping to increase the number of potential authors since scientists who generally do not use histochemistry in their research will find hints for the applications of histochemical techniques to novel still unexplored subjects.

Secretion of immunomodulating neuropeptides (VIP, SP) and nitric oxide synthase in porcine small intestine during postnatal development

Immunohistological identification/localization of immunomodulating neuropeptides [vasoactive intestinal polypeptide (VIP) and substance P (SP)] and enzyme nitric oxide synthase (NOS) as well as histomorphometric analyses of kinetics of their release and development of respective nerve fibers density during postnatal ontogenesis of porcine intestinal mucosal immune system (IMIS), were performed in order to assess the role of these molecules involved in maturation of the IMIS. The kinetcs of reactions to VIP, SP and NOS were demonstrated in the samples of jejunum and ileum from conventionally reared pigs. The samples were obtained at 0, 7, 14, 21, 28, 35, 42 and 49 days of age and processed for immunohistological staining. The VIP⁺ reaction was prevalently visible in the epithelial layer, lamina propria and Lieberkühn crypts (Lc) but also in the submucosa and lamina muscularis along blood and lymphatic vessels. The SP⁺ fibers were regularly distributed along enteric neurons in the muscular layer. The reaction to NOS was demonstrated in both mucosa and submucosa of ileum and jejunum and in the ileal Peyer's patches (PP). Intensity of the reaction was more pronounced in the epithelial layer and numerous NOS⁺ cells were observed around the Lc and inside the follicles of the PP. Also, we have noticed NOS⁺ blood vessels, particular neurons and nerve fibers in the submucosa and muscular layer of the small intestine. By analyzing quantitative patterns of SP⁺, VIP⁺ fibers and release of NOS we have concluded that intensity of their reactions gradually increases with age, except a short period of stagnation after weaning (at age of 28 days), reaching the highest values in the pigs aged between 42 and 49 days. The values obtained by Sperman rank order correlation test (rs) between days of age of pigs and intensity of the reactions in their jejunum/ileum to VIP (r_s=0.97/0.95), SP (r_s=0.97/0.97) and NOS (r_s=0.98/0.95), respectively, showed positive correlations (P<0.05) according to Roemer Orphal scale. Current study showed that post-natal development of porcine IMIS was accompanied by a substantial increase in the secretion of neuropeptides/enzyme tested and that these molecules may participate in the functional maturation of immunoregulatory/bactericidal mechanisms of the local (intestinal) immune defense in young pigs.

Increased number of intestinal villous M cells in levamisole -pretreated weaned pigs experimentally infected with F4ac⁺ enterotoxigenic Escherichia coli strain

Immunoprophylaxis of porcine postweaning colibacillosis (PWC) caused by enterotoxigenic Escherichia coli (ETEC) expressing F4 fimbriae is an unsolved problem. Just as ETEC strains can exploit intestinal microfold (M) cells as the entry portal for infection, their high transcytotic ability make them an attractive target for mucosally delivered vaccines, adjuvants and therapeutics. We have developed a model of parenteral/oral immunization of 4-weeks-old pigs with either levamisole or vaccine candidate F4ac⁺ non-ETEC strain to study their effects on de novo differentiation of antigen-sampling M cells. Identification, localization and morphometric quantification of cytokeratin 18 positive M cells in the ileal mucosa of 6-weeks-old pigs revealed that they were: 1) exclusively located within villous epithelial layer, 2) significantly numerous (P< 0.01) in levamisole pretreated/challenged pigs, and 3) only slightly, but not significantly numerous in vaccinated/challenged pigs compared with non-pretreated/challenged control pigs. The fact that levamisole may affect the M cells frequency by increasing their numbers, makes it an interesting adjuvant to study development of an effective M cell-targeted vaccine against porcine PWC.

Identifying pathological biomarkers: histochemistry still ranks high in the omics era

In recent years, omic analyses have been proposed as possible approaches to diagnosis, in particular for tumours, as they should be able to provide quantitative tools to detect and measure abnormalities in gene and protein expression, through the evaluation of transcription and translation products in the abnormal vs normal tissues. Unfortunately, this approach proved to be much less powerful than expected, due to both intrinsic technical limits and the nature itself of the pathological tissues to be investigated, the heterogeneity deriving from polyclonality and tissue phenotype variability between patients being a major limiting factor in the search for unique omic biomarkers. Especially in the last few years, the application of refined techniques for investigating gene expression in situ has greatly increased the diagnostic/prognostic potential of histochemistry, while the progress in light microscopy technology and in the methods for imaging molecules in vivo have provided valuable tools for elucidating the molecular events and the basic mechanisms leading to a pathological condition. Histochemical techniques thus remain irreplaceable in pathologist's armamentarium, and it may be expected that even in the future histochemistry will keep a leading position among the methodological approaches for clinical pathology.

Histochemistry through the years, browsing a long-established journal: novelties in traditional subjects

Histochemical journals represent a traditional forum where methodological and technological improvements can be presented and validated in view of their applications to investigate not only cytology and histology in normal and diseased conditions but to test as well hypotheses on more basic issues for life sciences, such as comparative and evolutionary biology. The earliest scientific journals on histochemistry began their publication in the first half of the ‘50s of the last century, and their readership did not probably change over the years; rather, the authors’ interests may have progressively been changing as well as the main topics of their articles. This hypothesis is discussed, based on the subjects of the article published in the first and last ten years in the European Journal of Histochemistry, as an example of old journal which started publication in 1954, being since then the official organ of the Italian Society of Histochemistry. This survey confirmed that histochemistry has provided and still offers unique opportunities for studying the structure, chemical composition and function of cells and tissues in a wide variety of living organisms, especially when the topological distribution of specific molecular components has diagnostic or predictive significance, as it occurs in human and veterinary biology and pathology. Some subjects (e.g. histochemistry applied to muscle cells or to mineralized tissues) have recently become rather popular, whereas a wider application of the histochemical approach may be envisaged for plant cells and tissues.