Host defense peptides (HDPs) show both antimicrobial and immunomodulatory properties making them important mediators of the host immune system. In humans but also in pigs many HDPs have been identified and important families such as cathelicidins and defensins have been established. In our study, we assessed: (i) the potential interactions that could occur between three peptides (LL37, PR39, and synthetic innate defense regulator (IDR)-1002) and a common TLR ligand called poly(I:C); (ii) the impact of selected peptides on the response of alveolar macrophage (AM) to poly(I:C) stimulation; (iii) the anti-porcine respiratory and reproductive syndrome virus (PRRSV) properties of the peptides; and (iv) their adjuvant potential in a PRRSV challenge experiment after immunization with different vaccine formulations. The results are as following: LL37, PR39, and IDR-1002 were able to interact with poly(I:C) using an agarose gel migration assay. Then, an alteration of AM's response to poly(I:C) stimulation was observed when the cells were co-stimulated with LL37 and IDR-1002. Regarding the anti-PRRSV potential of the peptides only LL37 showed a PRRSV inhibition in infected AM as well as precision cut lung slices (PCLS). However, in our conditions and despite their immunomodulatory properties, neither LL37 nor IDR-1002 showed any convincing potential as an adjuvant when associated to killed PRRSV in a challenge experiment. In conclusion, both antiviral and immunomodulatory properties could be identified for LL37, only immunomodulatory properties for IDR-1002, and both peptides failed to improve the immune response consecutive to an immunization with a killed vaccine in a PPRSV challenge experiment. However, further studies are needed to fully decipher and explain differences between peptide properties.

Staphylococcal superantigens cause toxic shock syndrome, which is characterized by massive T cell activation and a predominant Th1 profile of cytokine production. However, superantigen-producing Staphylococcus aureus strains are often part of the human nasal microbiome, and this carrier state has often been associated with some type 2 immune responses such as chronic sinusitis with polyps and atopic dermatitis. We have previously reported that the S. aureus cell wall downregulates the human T cell response to superantigens through a TLR2-dependent, IL-10-mediated mechanism. In this study, we show that S. aureus also regulates the profile of superantigen-induced T cell recruitment. The staphylococcal superantigen SEE induced the production of Th1 cell-recruiting chemokines, including IP-10, through an IFN-gamma-dependent mechanism. Such an induction was suppressed by the concomitant presence of S. aureus. The downregulation of IP-10 by S. aureus was mediated by components of its cell wall, but was not due to peptidoglycan-induced IL-10 production. Instead, S. aureus triggered activation of MAPKs p38 and ERK, as well as inhibition of STAT1 signaling in monocytes, altogether contributing to the downregulation of IP-10 and other Th1 cellrecruiting chemokines (e. g., CXCL9 and CXCL11). These effects translated into inhibition of superantigen-induced Th1 cell recruitment. Taken together, our data may explain why colonization of superantigen-producing S. aureus can induce, under some circumstances, mucosal type 2 immune responses.

The first step of HIV infection involves the interaction of the gp120 envelope glycoprotein to its receptor CD4, mainly expressed on CD4+ T cells. Besides its role on HIV-1 entry, the gp120 has been shown to be involved in the production of IL-1, IL-6, CCL20 and other innate response cytokines by bystander, uninfected CD4+ T cells and monocytes. However, the gp120 determinants involved in these functions are not completely understood. Whether signalling leading to cytokine production is due to CD4 or other receptors is still unclear. Enhanced chemokine receptor binding and subsequent clustering receptors may lead to cytokine production. By using a comprehensive panel of gp120 mutants, here we show that CD4 binding is mandatory for cytokine outburst in monocytes. Our data suggest that targeting monocytes in HIV-infected patients might decrease systemic inflammation and the potential tissue injury associated with the production of inflammatory cytokines. Understanding how gp120 mediates a cytokine burst in monocytes might help develop new approaches to improve the chronic inflammation that persists in these patients despite effective suppression of viremia by antiretroviral therapy.

ABSTRACT Staphylococcus aureus is a Gram-positive bacterium that is carried by a quarter of the healthy human population and that can cause severe infections. This pathobiosis has been linked to a balance between Toll-like receptor 2 (TLR2)-dependent pro- and anti-inflammatory responses. The relationship between these two types of responses is unknown. Analysis of 16 nasal isolates of S. aureus showed heterogeneity in their capacity to induce pro- and anti-inflammatory responses, suggesting that these two responses are independent of each other. Uncoupling of these responses was corroborated by selective signaling through phosphoinositol 3-kinase (PI3K)-Akt-mTOR and extracellular signal-regulated kinase (ERK) for the anti-inflammatory response and through p38 for the proinflammatory response. Uncoupling was also observed at the level of phagocytosis and phagosomal processing of S. aureus , which were required solely for the proinflammatory response. Importantly, the anti-inflammatory properties of an S. aureus isolate correlated with its ability to modulate T cell immunity. Our results suggest the presence of anti-inflammatory TLR2 ligands in the staphylococcal cell wall, whose identification may provide templates for novel immunomodulatory drugs.

•The microbiome plays an important role in determining the health status of the host.•The cytokine interleukin-10 (IL-10) is emerging as an important player of this role.•Microbiota-immune cell interactions balance commensalism and pathogenicity.•Novel strategies targetting IL-10 may have therapeutic potential.

The current review focuses on pre- and post-natal development of intestinal immunoglobulin A (IgA) production in pig. IgA production is influenced by intrinsic genetic factors in the foetus as well as extrinsic environmental factors during the post-natal period. At birth, piglets are exposed to new antigens through maternal colostrums/milk as well as exogenous microbiota. This exposure to new antigens is critical for the proper development of the gut mucosal immune system and is characterized mainly by the establishment of IgA response. A second critical period for neonatal intestinal immune system development occurs at weaning time when the gut environment is exposed to new dietary antigens. Neonate needs to establish oral tolerance and in the absence of protective milk need to fight potential new pathogens. To improve knowledge about the immune response in the neonates, it is important to identify intrinsic and extrinsic factors which influence the intestinal immune system development and to elucidate their mechanism of action.

Adjuvants are crucial components of vaccines. They significantly improve vaccine efficacy by modulating, enhancing, or extending the immune response and at the same time reducing the amount of antigen needed. In contrast to previously licensed adjuvants, current successful adjuvant formulations often consist of several molecules, that when combined, act synergistically by activating a variety of immune mechanisms. These “combination adjuvants” are already registered with several vaccines, both in humans and animals, and novel combination adjuvants are in the pipeline. With improved knowledge of the type of immune responses needed to successfully induce disease protection by vaccination, combination adjuvants are particularly suited to not only enhance, but also direct the immune responses desired to be either Th1-, Th2- or Th17-biased. Indeed, in view of the variety of disease and population targets for vaccine development, a panel of adjuvants will be needed to address different disease targets and populations. Here, we will review well-known and new combination adjuvants already licensed or currently in development—including ISCOMs, liposomes, Adjuvant Systems Montanides, and triple adjuvant combinations—and summarize their performance in preclinical and clinical trials. Several of these combination adjuvants are promising having promoted improved and balanced immune responses.

The development of vaccines for infants and young children requires the use of animal models at various stages of preclinical development. Animal models are being used to assess the quantity and quality of the immune response, onset and duration of the response, induction of systemic versus local immunity, protection against challenge infection for the assessment of vaccine efficacy, as well as safety and toxicity of the vaccine formulation itself. A variety of animal models are available, each with its own specific advantages and disadvantages. Here, we review the most common animal models for preclinical vaccine development for human infants.

In pigs raised for meat production, weaning is a critical period because of related physiological perturbations and negative consequences on performance. Previous studies have shown that early weaning could either impair development of mucosal barrier function or boost intestinal immunologic parameters. In order to obtain further knowledge about the impact of ultra-early weaning on the porcine immune system development, three groups of piglets were weaned at different ages and compared to the unweaned control group. Lower IgA concentrations in ultra-early and early weaned piglets than in other piglets were identified in serum. In the mesenteric lymph node (MLN), significant differences in the mRNA expression of IL17a, TGF beta and FOXP3 were found between specific groups. Indeed, IL17a mRNA was mainly detected in ultra-early weaned piglets while FOXP3 and TGF beta mRNA were associated to both ultra-early weaned and suckling piglets. Reduced serum IgA concentration and MLN induction of a Th17 cytokine in ultra-early weaned piglets could be related to alterations of the mucosal barrier functions consecutive to the milk deprivation. All together, our findings suggest a crucial role for endogenous milk factors onto the onset of IgA synthesis.

In many species such as sheep and pig, there are two types of Peyer's patches (PP): several discrete patches in the jejunum and a long and continuous patch in the ileum. Most of the immunoglobulin A in the gut is generated by B-cells in the PP germinal centers. Moreover, swine like ovine ileal PP might be important for antigen independent B-cell repertoire diversification. We examined, by quantitative real-time PCR, the expression of 36 transcripts of antimicrobial peptides, chemokines, interleukines, Toll-like receptors and transcription factors from both PP and we highlighted the differences by a principal component analysis. Ileal PP was characterized by a higher mRNA expression of CCL28, IL5, IL10, TLR2 and TLR4 while jejunal PP showed higher mRNA expression of antimicrobial peptides, CCL25, FOXP3, IL4, T-Bet, TSLP and SOCS2. Then, we analyzed some VDJ rearrangements to assess immunoglobulin repertoire diversity in jejunal and ileal PP from weaned piglets. The IgA and IgM repertoires were more diverse in ileal than in jejunal piglet PP. All these results could be related to the rarefaction of interfollicular T-cell zone and the presence in ileal versus jejunal lumen of a more diversified microflora. These findings shed a light on the functional differences between both PP.

Salmonella enterica subspecies enterica serovar Typhimurium, commonly called S. Typhimurium, can cause intestinal infections in humans and various animal species such as swine. To analyze the host response to Salmonella infection in the pig we used an in vivo gut loop model, which allows the analysis of multiple immune responses within the same animal. Four jejunal gut-loops were each inoculated with 3 x 10(8) cfu of S. Typhimurium in 3 one-month-old piglets and mRNA expressions of various cytokines, chemokines, transcription factors, antimicrobial peptides, toll like and chemokine receptors were assessed by quantitative real-time PCR in the Peyer's patch and the gut wall after 24 h. Several genes such as the newly cloned CCRL1/CCX-CKR were assessed for the first time in the pig at the mRNA level. Pro-inflammatory and T-helper type-1 (Th1) cytokine mRNA were expressed at higher levels in infected compared to non-infected control loops. Similarly, some B cell activation genes, NOD2 and toll like receptor 2 and 4 transcripts were more expressed in both tissues while TLR5 mRNA was down-regulated. Interestingly, CCL25 mRNA expression as well as the mRNA expressions of its receptors CCR9 and CCRL1 were decreased both in the Peyer's patch and gut wall suggesting a potential Salmonella strategy to reduce lymphocyte homing to the intestine. In conclusion, these results provide insight into the porcine innate mucosal immune response to infection with entero-invasive microorganisms such as S. Typhimurium. In the future, this knowledge should help in the development of improved prophylactic and therapeutic approaches against porcine intestinal S. Typhimurium infections.

Orientation of the immune response toward Th1, Th2, Th17 or Treg plays an important role in self-tolerance and defence against pathogens and tumors. However, this orientation has not been fully characterised in the pig and little is known about the influence of maturation stimulus on the capacity of dendritic cells selectively to direct different types of Th cell responses. Dendritic cell (DC) maturation can be induced by different agents such as inflammatory cytokines, TLR ligands and CD40L. However, the role of the latter in the maturation of pig DC has never been reported. In this study we analysed how different maturation agents influence the capacity of DC to skew the immune response. Monocyte-derived porcine DCs were matured with human CD40L-transfected L-cells, Lipopolysaccharide (LPS) alone or LPS in combination with Tumor necrosis factor-alpha (TNFalpha) and interferon-alpha (IFNalpha). We found that human CD40L induced DC maturation characterised by increased expression of co-stimulatory CD80/86 molecules, high production of IL-12p40 in DC and induction of IFNgamma and t-bet mRNA in T cells, suggesting a Th1 orientation. Moreover we report for the first time the appearance of CD25 after activation of porcine DC. Furthermore, DC activated with TNF+LPS+IFN showed the highest allo-stimulatory capacity of allogeneic lymphocytes and induced IL-17 mRNA in T lymphocytes, suggesting a Th17 orientation that has never been previously reported in the pig. We also showed that immature DCs did not produce any IL-10 or IL-12 and induced both GATA-3 and IL-13 transcription in allogeneic MLR suggesting a Th2 orientation. This study therefore underlines that the nature of the stimulus strongly influences the capacity of DC to steer the immune response in the pig.

In monogastric mammals, transfer of passive immunity via milk and colostrum plays an important role in protecting the neonate against mucosal infections. Here we analyzed the hypothesis that during gestation/lactation IgA+ plasmablasts leave the intestinal and respiratory surfaces towards the mammary gland (MG). We compared the recruitment of lymphocytes expressing homing receptors α4β1 and α4β7 to expression of their vascular counter-receptors, VCAM-1 and MAdCAM-1. Furthermore, the expression of the chemokines responsible for the recruitment of IgA+ plasmablasts was analyzed. Data confirmed that expressions of CCL28 and MAdCAM-1 in the MG increased during pregnancy and α4β1+ and α4β7+/IgA+ cell recruitment in lactation correlated with increase of CCL28 expression. Interestingly, VCAM-1 expression was found in small blood vessels of the lactating porcine MG, while in mice VCAM-1 was expressed in large blood vessels within the MG. Thus, our results indicate that the recruitment of IgA+ plasmablasts to MG is mediated by VCAM-1/α4β1 and MAdCAM-1/α4β7 in conjunction with CCL28/CCR10. They support the existence of a functional link between entero- and upper respiratory surfaces and MG, thereby, conferring protection against aero-digestive pathogens in the newborn.