Monocyte-derived dendritic cells enhance cell proliferation and porcine circovirus type 2 replication in concanavalin A-stimulated swine peripheral blood lymphocytes in vitro

Proliferation of peripheral blood mononuclear cells from healthy piglets after mitogen stimulation as indicators of disease resilience

Disease resilience refers to the productivity of an animal under disease. Given the high biosecurity of pig nucleus herds, traits that can be measured on healthy pigs and that are genetically correlated with disease resilience, that is, genetic indicator traits, offer a strategy to select for disease resilience. Our objective was to evaluate mitogen stimulation assays (MSAs) on peripheral blood mononuclear cells (PBMCs) from young healthy pigs as genetic indicators for disease resilience. Data were from a natural disease challenge in which batches of 60 or 75 naïve Yorkshire × Landrace piglets were introduced every 3 wk into a continuous flow barn that was seeded with multiple diseases. In this environment, disease resilience traits, including growth, treatment, and mortality rates, were recorded on 3,136 pigs that were genotyped with a high-density marker panel. PBMCs from 882 of these pigs from 19 batches were isolated from whole blood collected prior to the disease challenge and stimulated with five mitogens: concanavalin A (ConA), phytohemagglutinin (PHA), pokeweed mitogen (PWM), lipopolysaccharide (LPS), and phorbol myristate acetate (PMA). The proliferation of cells was evaluated at 48, 72, and 96 h and compared with unstimulated samples (rest count). Heritabilities of cell proliferation were estimated using a model with batch as a fixed effect and covariates of entry age; rest count; complete blood count proportions of lymphocytes, monocytes, eosinophils, and basophils; and pen, litter, and animal genetics as random effects. Heritability estimates were highest for response to ConA (0.30 ± 0.09, 0.28 ± 0.10, 0.17 ± 0.10, and 0.25 ±0.10 at 48, 72, and 96 h after stimulation and for area under the curve across the three time points, respectively). Estimates were in a similar range for response to PHA and PMA but low for PWM and LPS. Responses to ConA, PHA, and PMA were moderately genetically correlated with several disease resilience traits and in the expected direction, but individual estimates were not significantly different from zero due to large SEs. In conclusion, although validation is needed, MSAss, in particular based on ConA, show promise as genetic indicator traits for disease resilience.

Porcine Dendritic Cells and Viruses: An Update

Several viral infections of swine are responsible for major economic losses and represent a threat to the swine industry worldwide. New tools are needed to prevent and control endemic, emerging, and re-emerging viral diseases. Dendritic cells (DC) play a central role in linking the innate and adaptive arms of the immune system, so knowledge regarding their interaction with pathogens is necessary to understand the mechanisms underlying diseases pathogenesis and protection. In the first part of this review, we provide an update on the heterogeneous cell subsets that comprise the porcine DC family. In the second part of this review, we provide an overview of how three viruses, affecting pork production at a global level, African swine fever virus (ASFV), classical swine fever virus (CSFV), and porcine circovirus 2 (PCV2), modulate DC function.

Breed Differences in PCV2 Uptake and Disintegration in Porcine Monocytes

Porcine circovirus type 2 (PCV2) is associated with various diseases which are designated as PCV2-associated diseases (PCVADs). Their severity varies among breeds. In the diseased pigs, virus is present in monocytes, without replication or full degradation. PCV2 entry and viral outcome in primary porcine monocytes and the role of monocytes in PCV2 genetic susceptibility have not been studied. Here, virus uptake and trafficking were analyzed and compared among purebreds Piétrain, Landrace and Large White and hybrid Piétrain × Topigs20. Viral capsids were rapidly internalized into monocytes, followed by a slow disintegration to a residual level. PCV2 uptake was decreased by chlorpromazine, cytochalasin D and dynasore. The internalized capsids followed the endosomal trafficking pathway, ending up in lysosomes. PCV2 genome was nicked by lysosomal DNase II in vitro, but persisted in monocytes in vivo. Monocytes from purebred Piétrain and the hybrid showed a higher level of PCV2 uptake and disintegration, compared to those from Landrace and Large White. In conclusion, PCV2 entry occurs via clathrin-mediated endocytosis. After entry, viral capsids are partially disintegrated, while viral genomes largely escape from the pathway to avoid degradation. The degree of PCV2 uptake and disintegration differ among pig breeds.

Connexin 43 in splenic lymphocytes is involved in the regulation of CD4+CD25+ T lymphocyte proliferation and cytokine production in hypertensive inflammation

Chronic inflammation promotes the development of hypertension and is associated with increased T cell infiltration and cytokine production in impaired organs. Gap junction protein connexin 43 (Cx43), is ubiquitously expressed in immune cells and plays an important role in T cell proliferation and activation, and cytokine production. However, the correlation between Cx43 in T cells and the hypertensive inflammatory response remains unknown. Thus, in this study, we wished to examine this correlation. First, our results revealed that hypertension caused significant thickening of the vascular wall, inflammatory cell infiltration into part of the renal interstitium and glomerular atrophy, and it increased the tubular damage scores in the kidneys of spontaneously hypertensive rats (SHRs). Moreover, the SHRs exhibited stenosis in the central artery wall of the spleen with increased serum levels of interleukin (IL)-2 and IL-6 compared with normotensive Wistar-Kyoto (WKY) rats. The spleens of the SHRs exhibited a significantly decreased percentage of CD4⁺CD25⁺ (Treg) T cells. However, the percentages of CD3⁺, CD4⁺ and CD8⁺ T cell and the levels of CD4⁺Cx43 and CD8⁺Cx43 did not differ significantly between the SHRs and WKY rats. In cultured lymphocytes from the SHRs and WKY rats, low percentages of Treg cells and reduced cytokine (IL-2 and IL-6) mRNA expression levels were observed in the lymphocytes obtained from the SHRs and WKY rats treated with the connexin blocker, Gap27, or concanavalin A (ConA) plus Gap27. The effects of ConA and Gap27 differed between the SHRs and WKY rats. On the whole, our findings demonstrate that the splenic Treg cell-mediated suppression in SHRs may be involved in hypertensive inflammatory responses. Cx43 in the gap junctional channel may regulate lymphocyte activation and inflammatory cytokine production.

Generation of potent porcine monocyte-derived dendritic cells (MoDCs) by modified culture protocol

In vitro derivation of dendritic cells (DCs) is an alternative approach to overcome the low frequency of primary DCs and the difficulty of isolation techniques for studying DC immunobiology. To date, the conventional culture protocol of porcine monocyte-derived DCs (MoDCs) has been widely used. However, this protocol is not practical due to the requirement of a substantial number of blood monocytes, and the process often interferes with DC maturation. To improve in vitro porcine MoDC generation, we modified the previous conventional DC generation protocol, based on the human and mouse primary DC culture system, and compared phenotypic and functional features of MoDCs derived from the modified protocol to the conventional protocol. The modified protocol consumed fewer monocytes but generated higher CD1⁺ cells with DC-like morphology and the ability of maturation. In addition, MoDCs from the modified protocol exhibited increased antigen uptake and IFN-γ production in response to LPS stimulation. Our findings indicate that the modified protocol is expedient and reliable for generating potent MoDCs that substitute for primary DCs. This will be a valuable platform for future research in antigen delivery, vaccines and immunotherapy in pigs, as well as relevant veterinary species.

Comparative In Vitro and In Vivo Studies of Porcine Rotavirus G9P[13] and Human Rotavirus Wa G1P[8]

The changing epidemiology of group A rotavirus (RV) strains in humans and swine, including emerging G9 strains, poses new challenges to current vaccines. In this study, we comparatively assessed the pathogenesis of porcine RV (PRV) G9P[13] and evaluated the short-term cross-protection between this strain and human RV (HRV) Wa G1P[8] in gnotobiotic pigs. Complete genome sequencing demonstrated that PRV G9P[13] possessed a human-like G9 VP7 genotype but shared higher overall nucleotide identity with historic PRV strains. PRV G9P[13] induced longer rectal virus shedding and RV RNAemia in pigs than HRV Wa G1P[8] and generated complete short-term cross-protection in pigs challenged with HRV or PRV, whereas HRV Wa G1P[8] induced only partial protection against PRV challenge. Moreover, PRV G9P[13] replicated more extensively in porcine monocyte-derived dendritic cells (MoDCs) than did HRV Wa G1P[8]. Cross-protection was likely not dependent on serum virus-neutralizing (VN) antibodies, as the heterologous VN antibody titers in the sera of G9P[13]-inoculated pigs were low. Thus, our results suggest that heterologous protection by the current monovalent G1P[8] HRV vaccine against emerging G9 strains should be evaluated in clinical and experimental studies to prevent further dissemination of G9 strains. Differences in the pathogenesis of these two strains may be partially attributable to their variable abilities to replicate and persist in porcine immune cells, including dendritic cells (DCs). Additional studies are needed to evaluate the emerging G9 strains as potential vaccine candidates and to test the susceptibility of various immune cells to infection by G9 and other common HRV/PRV genotypes.

IMPORTANCE

The changing epidemiology of porcine and human group A rotaviruses (RVs), including emerging G9 strains, may compromise the efficacy of current vaccines. An understanding of the pathogenesis and genetic, immunological, and biological features of the new emerging RV strains will contribute to the development of new surveillance and prevention tools. Additionally, studies of cross-protection between the newly identified emerging G9 porcine RV strains and a human G1 RV vaccine strain in a susceptible host (swine) will allow evaluation of G9 strains as potential novel vaccine candidates to be included in porcine or human vaccines.

PCV2 on the spot-A new method for the detection of single porcine circovirus type 2 secreting cells

A porcine circovirus type 2 SPOT (PCV2-SPOT) assay was established to enumerate virus-secreting lymphocytes obtained from naturally infected pigs. The assay is based on the same principle as general ELISPOT assays but instead of detecting cytokine or immunoglobulin secretion, PCV2 particles are immobilized and detected as filter spots. The method was used to evaluate the influence of various cell activators on the PCV2 secretion in vitro and was also applied to study the PCV2 secretion by lymphocytes obtained from pigs in healthy herds and in a herd afflicted by postweaning multisystemic wasting disease (PMWS). Peripheral blood mononuclear cells (PBMCs) obtained from a pig with severe PMWS produced PCV2-SPOTs spontaneously whereas PBMCs obtained from pigs infected subclinically only generated PCV2-SPOTs upon in vitro stimulation. The PCV2 secretion potential was related to the PCV2 DNA content in the PBMCs as determined by two PCV2 real-time PCR assays, developed to differentiate between Swedish PCV2 genogroups 1 (PCV2a) and 3 (PCV2b). Besides the current application these qPCRs could simplify future epidemiological studies and allow genogroup detection/quantitation in dual infection experiments and similar studies. The developed PCV2-SPOT assay offers a semi-quantitative approach to evaluate the potential of PCV2-infected porcine cells to release PCV2 viral particles as well as a system to evaluate the ability of different cell types or compounds to affect PCV2 replication and secretion.

Immunomodulatory Activities of α-Mangostin on Peripheral Blood Mononuclear Cells

Mangosteen ( Garcinia mangostana L.) a tropical fruit, has been used in traditional medicine. A frequently used part of mangosteen is the pericarp, containing a high content of xanthones. α-Mangostin, one of the major xanthone derivatives, exhibits a variety of actions, including antimicrobial, antioxidant, cytotoxic and antitumor; however, its function on the immune system is still equivocal. This study aimed to examine the immunomodulatory activities of α-mangostin on lymphocyte lineage and cytokine production in human peripheral blood mononuclear cells (PBMCs). The cytotoxic activity of α-mangostin was measured by MTT assay. The concentration of α-mangostin at 5.55 μg/mL resulted in a 50% survival of PBMCs, which was as potent a cytotoxic activity as that of paclitaxel. After 24 h of PBMCs culture, the percentages of T cells (CD3+), B cells (CD19+) and NK cells (CD3-CD16+CD56+) were not significantly changed by treatment with 1, 2 and 4 μg/mL of α-mangostin compared with untreated-PBMCs; in addition, the percentages of these lymphocytes treated with the combination of α-mangostin (1, 2 and 4 μg/mL) and the mitogen concanavalin A (ConA) was not significantly different from that of ConA-treated PBMCs. For cytokine secretion, α-mangostin (1, 2 and 4 μg/mL) did not significantly induce either proinflammatory cytokines (i.e., TNF-α and IL-1β) or cytokine of adaptive immunity (i.e., IL-2). The combination of α-mangostin (1, 2 and 4 μg/mL) and ConA did not significantly alter the relative difference of TNF-α and IL-1β compared with ConA-treated PBMCs; however, these combinations could significantly decrease the relative difference of IL-2 compared with ConA-treated PBMCs. These data indicated that α-mangostin was able to inhibit IL-2 release without interfering with human immune cells; therefore, further studies are necessary to investigate its effect on IL-2 production.