Immune response toCystoisospora suisin piglets: local and systemic changes in T-cell subsets and selected mRNA transcripts in the small intestine

Swine unconventional T cells

Pigs are important domestic livestock and a comprehensive understanding of their immune system is critical to improve swine vaccine efficacy. Pig models represent an excellent animal model for immunological studies because of their anatomical and physiological similarities to humans. A significant portion of pig immunological studies focused on characterizing the conventional T cell (Tconv) immune responses. These cells recognize peptides presented by major histocompatibility complex (MHC) proteins. In contrast, unconventional T cells are non-MHC-restricted and profoundly regulate conventional T cells. Key subsets of unconventional T cells reviewed here include natural killer T (NKT) cells, γδ T cells, mucosal-associated invariant T (MAIT) cells, intraepithelial lymphocytes (IELs), and two potential unconventional T cell subsets expressing NKp46 or CD11b. Unlike Tconvs, most of these cells recognize lipids, small molecule metabolites, or modified peptides, and they generally show simplified patterns of T cell receptor (TCR) expression and rapid effector responses. Here, we review that unconventional T cells are an abundant and critical component of the porcine immune system, summarize the current understanding of these cells, and highlight some of the key differences among mouse, human, and porcine unconventional T cells.

A porcine model of subcutaneous Staphylococcus aureus infection: a pilot study

In this descriptive pilot study, we aim to establish a porcine Staphylococcus aureus skin infection model by subcutaneous injection (s.c.) of the porcine S54F9 S. aureus strain in the groin area. Six pigs were used in the study: Five pigs were injected with S. aureus, inocula ranging from 7 × 10³ to 5 × 10⁷ colony-forming units per kg bodyweight; one pig was injected with saline exclusively. Lesions were recorded up to 6 days postinoculation using clinical evaluation, ultrasound evaluation, microbiology, flow cytometry, and pathology. Inoculation gave rise to lesions ranging from localized skin infection, that is, minute histological changes, intracellular infection, and macroscopic abscess formation with sequestration of soft tissue, to generalized infection and development of disseminated intravascular coagulation necessitating euthanasia only 10 h after inoculation. Ultrasound assessment of maximum width and characteristics was not able to disclose the progress of the local infection. Flow cytometry and immunohistochemistry revealed the participation of γδT cells in the immune response. In conclusion, we did see a graded inflammatory response associated with the dose of s.c. inoculated bacteria, which may be useful for studying, in particular, the interaction of bacteria and inflammatory mononuclear cell populations. It needs to be investigated if the model is discriminatory and robust.

Antibody and cytokine response to Cystoisospora suis infections in immune-competent young pigs

Background

To date, investigations on the immune response to Cystoisospora suis infections focused on suckling piglets, the age group clinically most affected. Actively immunizing piglets is unfeasible due to their immature immune system and the typically early infection in the first days after birth. Therefore, understanding and possibly enhancing the immune response of immune-competent animals is the prerequisite to develop a passive immunization strategy for piglets which currently rely on very limited treatment options.

Methods

To investigate antibody and cytokine responses of immune-competent animals and the impact of the oral immunization protocol on their immune response, growers with unknown previous exposure to C. suis (10–11 weeks-old) were infected one or three times with different doses (600 and 6000 or 200 and 2000, respectively) of C. suis oocysts, and compared to uninfected controls. Oocyst excretion was evaluated, and blood and intestinal mucus antibody titers were determined by IFAT. Systemic production of Th1, Th2, inflammatory and regulatory cytokines was determined in different immune compartments at mRNA and (after stimulation with a recombinant merozoite-protein) at protein level by PCR and multiplex fluorescent immunoassay, respectively.

Results

Infection generated significantly increased serum IgA and IgG levels against C. suis sporozoites and merozoites, irrespective of infection mode, with IgG against merozoites showing the strongest increase. No clinical signs and only occasional excretion were observed. The systemic cytokine response to C. suis was only weak. Nonetheless, in white blood cells, IL-4, IL-6 and IL-10 mRNA-levels significantly increased after infection, whereas IFN-ɣ, IL-2 and TGF-β expression tended to decrease. In mesenteric lymph nodes (MLN), IL-10 and TNF-α levels were elevated while splenic cytokine expression was unaltered upon infection. Stimulated MLN-derived lymphocytes from infected pigs produced slightly more IL-12 and less IFN-α than controls.

Conclusions

An infection and a subsequent systemic immune response can be induced in immune-competent animals by all evaluated infection models and growers can be used as models to mimic sow immunizations. The immune response to C. suis, although mild and with considerable variation in cytokine expression, was characterized by a Th2-associated and regulatory cytokine profile and antibody production. However, none of the parameters clearly stood out as a potential marker associated with protection. Antibody titers were significantly positively related with oocyst excretion and might thus serve as correlates for parasite replication or severity of infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2974-6) contains supplementary material, which is available to authorized users.

Clinical cystoisosporosis associated to porcine cytomegalovirus (PCMV, Suid herpesvirus 2) infection in fattening pigs

Cystoisospora (syn. Isospora) suis is the causative agent of neonatal porcine coccidiosis and one of the main causes of diarrhoea in suckling piglets worldwide. Infection with porcine cytomegalovirus (PCMV, Suid herpesvirus 2) causes inclusion body rhinitis in pigs. In a Swiss pig herd (n = 2 boars, 7 sows, 2 gilts, 18 finishing pigs, 30 fattening pigs, 54 suckling piglets), an outbreak of PCMV infection with high morbidity in all age categories, characterized by fever, anorexia, reduced general condition, respiratory signs and increased piglet mortality, was diagnosed by histopathology and molecular methods. Five fattening pigs (age ~ 17 weeks) additionally showed diarrhoea, not typical for PCMV infections, and one fattener had to be euthanized due to poor condition. Histopathologically, severe fibrinopurulent jejunoileitis with extensive atrophy and fusion of intestinal villi, loss of goblet cells and crypt abscesses associated to C. suis infection were present. In the liver, herpesvirus intranuclear inclusion bodies were observed and PCMV was confirmed by PCR/sequencing. No further infectious causes of diarrhoea (i.e. Rotavirus A; TGEV; PEDV; PCV-2; enterotoxigenic Escherichia coli or Lawsonia intracellularis) were detected in the euthanized fattener. Coproscopically, C. suis oocysts were identified in the faeces from further fatteners with diarrhoea. While C. suis usually produces disease only in suckling piglets, its association with severe intestinal lesions and diarrhoea in ~ 17-week-old fatteners was surprising. It is supposed that the underlying PCMV infection might have contributed to the presentation of clinical cystoisosporosis in fattening pigs. The interaction mechanisms between these two pathogens are unknown.

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A Porcine Cytomegalovirus (PCMV) outbreak was diagnosed in a Swiss pig herd

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Cystoisospora suis caused diarrhoea in 17 week-old fattening pigs co-infected with PCMV

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PCMV infection may produce immunosuppression in pigs

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PCMV may have contributed to presentation of clinical cystoisosporosis in fattening pigs

The genome of the protozoan parasite Cystoisospora suis and a reverse vaccinology approach to identify vaccine candidates

Vaccine development targeting protozoan parasites remains challenging, partly due to the complex interactions between these eukaryotes and the host immune system. Reverse vaccinology is a promising approach for direct screening of genome sequence assemblies for new vaccine candidate proteins. Here, we applied this paradigm to Cystoisospora suis, an apicomplexan parasite that causes enteritis and diarrhea in suckling piglets and economic losses in pig production worldwide. Using Next Generation Sequencing we produced an ∼84Mb sequence assembly for the C. suis genome, making it the first available reference for the genus Cystoisospora. Then, we derived a manually curated annotation of more than 11,000 protein-coding genes and applied the tool Vacceed to identify 1,168 vaccine candidates by screening the predicted C. suis proteome. To refine the set of candidates, we looked at proteins that are highly expressed in merozoites and specific to apicomplexans. The stringent set of candidates included 220 proteins, among which were 152 proteins with unknown function, 17 surface antigens of the SAG and SRS gene families, 12 proteins of the apicomplexan-specific secretory organelles including AMA1, MIC6, MIC13, ROP6, ROP12, ROP27, ROP32 and three proteins related to cell adhesion. Finally, we demonstrated in vitro the immunogenic potential of a C. suis-specific 42kDa transmembrane protein, which might constitute an attractive candidate for further testing.

Vaccination against parasites - status quo and the way forward

Although vaccination against various pathogens is integral to health management of swine, vaccines against parasites have not yet been commercialized for the use in pigs. The incentive to develop and commercialize anti-parasitic vaccines in swine are twofold; on the one hand parasitic diseases which are economically important, such as ascarosis and neonatal coccidiosis, could be controlled in a sustainable manner; on the other hand, the transmission of zoonotic parasites, such as Toxoplasma gondii or Cysticercus cellulosae, could be effectively interrupted. Although experimental research indicates that vaccination against a number of porcine parasites is feasible, development and commercialization of potential vaccines so far has been very slow, as our knowledge on the host-parasite interplay in porcine parasitic infections is still very limited. In the light of growing concerns regarding consumer health and antiparasitic drug resistance, however, it is timely to re-direct R&D efforts to the development of biological control options.

Polymerization-dependent activation of porcine γδ T-cells by proanthocyanidins

Plant-derived proanthocyanidins (PAC) have been promoted as a natural method of improving health and immune function in livestock. It has previously been shown that PAC are effective agonists for activating ruminant γδ T-cells in vitro, however effects on other livestock species are not yet clear. Moreover, the fine structural characteristics of the PAC which contribute to this stimulatory effect have not been elucidated. Here, we demonstrate activation of porcine γδ T-cells by PAC via up-regulation of CD25 (IL-2Rα) and show that 1) activation is dependent on degree of polymerization (DP), with PAC fractions containing polymers with mean DP >6 significantly more effective than fractions with mean DP <6, whilst flavan-3-ol monomers (the constituent monomeric units of PAC) did not induce CD25 expression and 2) both procyanidin and prodelphinidin-type PAC are effective agonists. Furthermore, we show that this effect of PAC is restricted to the γδ T-cell population within porcine peripheral mononuclear cells as significant CD25 up-regulation was not observed in non γδ T-cells, and no activation (via CD80/86 up-regulation) was evident in monocytes. Our results show that dietary PAC may contribute to enhancement of innate immunity in swine via activation of γδ T-cells.

Cystoisospora suis - A Model of Mammalian Cystoisosporosis

Cystoisospora suis is a coccidian species that typically affects suckling piglets. Infections occur by oral uptake of oocysts and are characterized by non-hemorrhagic transient diarrhea, resulting in poor weight gain. Apparently, primary immune responses to C. suis cannot readily be mounted by neonates, which contributes to the establishment and rapid development of the parasite, while in older pigs age-resistance prevents disease development. However, the presence of extraintestinal stages, although not unequivocally demonstrated, is suspected to enable parasite persistence together with the induction and maintenance of immune response in older pigs, which in turn may facilitate the transfer of C. suis-specific factors from sow to offspring. It is assumed that neonates are particularly prone to clinical disease because infections with C. suis interfere with the establishment of the gut microbiome. Clostridia have been especially inferred to profit from the altered intestinal environment during parasite infection. New tools, particularly in the area of genomics, might illustrate the interactions between C. suis and its host and pave the way for the development of new control methods not only for porcine cystoisosporosis but also for other mammalian Cystoisospora infections. The first reference genome for C. suis is under way and will be a fertile ground to discover new drugs and vaccines. At the same time, the establishment and refinement of an in vivo model and an in vitro culture system, supporting the complete life cycle of C. suis, will underpin the functional characterization of the parasite and shed light on its biology and control.