The mechanism of immune dysregulation caused by porcine reproductive and respiratory syndrome virus (PRRSV).

PRRSV is capable of evading the effective immune response, thus persisting in piglets and throughout the swine herd. We show here that PRRSV invades the thymus and causes depletion of T-cell precursors and alteration of the TCR repertoire. Developing thymocytes are affected during negative selection when they transit from the triple-negative to triple-positive stages at the corticomedullary junction just before entering the medulla. The restriction of repertoire diversification occurs in both helper and cytotoxic αß-T cells. As a result, critical viral epitopes are tolerated, and infection becomes chronic. However, not all viral epitopes are tolerated. Infected piglets develop antibodies capable of recognizing PRRSV, but these are not virus neutralizing. Further analysis showed that the lack of an effective immune response against the critical viral structures results in the absence of a germinal center response, overactivation of T and B cells in the periphery, robust production of useless antibodies of all isotypes, and the inability to eliminate the virus. Overall, the results show how a respiratory virus that primarily infects and destroys myelomonocytic cells has evolved strategies to disrupt the immune system. These mechanisms may be a prototype for how other viruses can similarly modulate the host immune system.

Modified live vaccine strains of porcine reproductive and respiratory syndrome virus cause immune system dysregulation similar to wild strains.

Introduction: Porcine reproductive and respiratory syndrome virus (PRRSV) emerged about 30 years ago and continues to cause major economic losses in the pork industry. The lack of effective modified live vaccines (MLV) allows the pandemic to continue. Background and objective: We have previously shown that wild strains of PRRSV affect the nascent T cell repertoire in the thymus, deplete T cell clones recognizing viral epitopes essential for neutralization, while triggering a chronic, robust, but ineffective antibody response. Therefore, we hypothesized that the current MLV are inappropriate because they cause similar damage and fail to prevent viral-induced dysregulation of adaptive immunity. Methods: We tested three MLV strains to demonstrate that all have a comparable negative effect on thymocytes in vitro. Further in vivo studies compared the development of T cells in the thymus, peripheral lymphocytes, and antibody production in young piglets. These three MLV strains were used in a mixture to determine whether at least some of them behave similarly to the wild virus type 1 or type 2. Results: Both the wild and MLV strains cause the same immune dysregulations. These include depletion of T-cell precursors, alteration of the TCR repertoire, necrobiosis at corticomedullary junctions, low body weight gain, decreased thymic cellularity, lack of virus-neutralizing antibodies, and production of non-neutralizing anti-PRRSV antibodies of different isotypes. Discussion and conclusion: The results may explain why the use of current MLV in young animals may be ineffective and why their use may be potentially dangerous. Therefore, alternative vaccines, such as subunit or mRNA vaccines or improved MLV, are needed to control the PRRSV pandemic.

A ferret model of immunosuppression induced with dexamethasone.

Ferrets are nowadays frequently used as animal models for biomedical purposes; in many cases, immunosuppression of experimental animals is necessary. The aim of this study was to evaluate the effect of intramuscular dexamethasone administration (2 mg/kg as the initiation dose continued with 1 mg/kg q 12 h applied 5 times) on ferret's immune system. In comparison with ferrets which received the saline (n = 5), significantly lower total counts of leukocytes (P < 0.01), lymphocytes (P < 0.01) and monocyte (P < 0.05), as well as absolute numbers of CD4+CD8- (P < 0.01) and CD4-CD8+ (P < 0.01) subsets were noted in dexamethasone treated ferrets (n = 5) the first day after the treatment (D1). Absolute number of CD79+ lymphocytes remained unchanged throughout the experiment. The proliferation activity of lymphocytes in dexamethasone treated ferrets was lower only in D1 using concanavalin A (conA), phytohemagglutinin (PHA) and pokeweed mitogen (PWM); statistical significance was noted using PHA 40 (P < 0.05) and PWM 10 (P < 0.01). Lower neutrophil activity (P < 0.01) was detected in D1 after the dexamethasone treatment in both production of reactive oxygen species (chemiluminescence test) and ingestion of particles (phagocytosis assay). The dexamethasone treatment proved to be useful for short-term immunosuppression in ferrets. The results closely resembled data previously reported in human studies and indicate classification of ferrets as steroid-resistant species.

The immune system of the ferret (Mustela putorius furo) - A review.

The basic information dealing with the anatomy of the ferret's immune system, cross-reactivity of the ferret leukocytes with polyclonal and monoclonal antibodies in vitro and immune response to the mitogens and various infections are presented. The leukocyte numbers in the peripheral blood in the ferrets are lower compared to other species and only one subclass of IgG has been identified in ferrets so far. Lymphocytes make up 12-67% of all the leukocytes in the peripheral blood of the healthy adult ferrets. Lymphocyte subpopulations are similar to other mammals and include T- and B-lymphocytes. T-lymphocytes differentiate into helper (Th) lymphocytes and cytotoxic (Tc) lymphocytes. Currently, ferret granulocytes (CD11), B-lymphocytes (CD79α), T-lymphocytes (CD3), Th-lymphocytes (CD3, CD4), Tc-lymphocytes (CD3, CD8), and CD30, CD45 subpopulations are detected with the use of a number of polyclonal as well as with monoclonal antibodies. In a lymphocyte transformation assay, the mitogen response of the peripheral blood mononuclear cells to concanavalin A (ConA), phytohaemagglutinin (PHA), and pokeweed mitogen (PWM) is the greatest at day 2, 2 and 3, respectively. Serious lymphopenia is observed in ferrets during a distemper infection. A significant decrease in the lymphocyte transformation activity is observed on day 5 and reaches a maximal decrease on days 8-11, with full recovery on days 23-30 after the inoculation of laboratory ferrets with the distemper virus. Ferrets have also been used in studies related to the function of the immune system in Helicobacter pylori infections, Crohn's disease and bronchial asthma.

Dynamics and Differences in Systemic and Local Immune Responses After Vaccination With Inactivated and Live Commercial Vaccines and Subsequent Subclinical Infection With PRRS Virus.

The goals of our study were to compare the immune response to different killed and modified live vaccines against PRRS virus and to monitor the antibody production and the cell mediated immunity both at the systemic and local level. In the experiment, we immunized four groups of piglets with two commercial inactivated (A1-Progressis, A2-Suivac) and two modified live vaccines (B3-Amervac, B4-Porcilis). Twenty-one days after the final vaccination, all piglets, including the control non-immunized group (C5), were i.n., infected with the Lelystad strain of PRRS virus. The serum antibody response (IgM and IgG) was the strongest in group A1 followed by two MLV (B3 and B4) groups. Locally, we demonstrated the highest level of IgG antibodies in bronchoalveolar lavages (BALF), and saliva in group A1, whereas low IgA antibody responses in BALF and feces were detected in all groups. We have found virus neutralization antibody at DPV 21 (days post vaccination) and higher levels in all groups including the control at DPI 21 (days post infection). Positive antigen specific cell-mediated response in lymphocyte transformation test (LTT) was observed in groups B3 and B4 at DPV 7 and in group B4 at DPV 21 and in all intervals after infection. The IFN-γ producing lymphocytes after antigen stimulation were found in CD4-CD8+ and CD4+CD8+ subsets of all immunized groups 7 days after infection. After infection, there were obvious differences in virus excretion. The virus was detected in all groups of piglets in serum, saliva, and occasionally in feces at DPI 3. Significantly lower virus load was found in groups A1 and B3 at DPI 21. Negative samples appeared at DPI 21 in B3 group in saliva. It can be concluded that antibodies after immunization and infection, and the virus after infection can be detected in all the compartments monitored. Immunization with inactivated vaccine A1-Progressis induces high levels of antibodies produced both systemically and locally. Immunization with MLV-vaccines (Amervac and Porcilis) produces sufficient antibody levels and also cell-mediated immunity. After infection virus secretion gradually decreases in group B3, indicating tendency to induce sterile immunity.

Monocyte derived macrophages as an appropriate model for porcine cytomegalovirus immunobiology studies.

Porcine cytomegalovirus (PCMV) causes lifelong latent infections in swine. The pathogen is occasionally associated with inclusion body rhinitis and pneumonia in piglets, reproductive disorders in pregnant sows and respiratory disease complex in older pigs. Immunosuppressive potential of PCMV infection is discussed. Macrophages were recognised as one of target cell types where propagation of virus occurs. The aim of present study was to set up model PCMV infection of monocyte derived macrophages (MDMs) in vitro for PCMV immunobiology research. Obtained results showed that PCMV is able to infect and propagate in MDMs. Possible immunosuppressive effect of PCMV on infected macrophages was evaluated by measurement of immune relevant gene expression in MDMs. Infection decreased expression of IL-8 and TNF-α (pro-inflammatory cytokines) and increased expression of IL-10 (anti-inflammatory cytokine) on mRNA transcription level. Obtained data support hypothesis that higher sensitivity of animals to coinfection with other swine pathogens and its more severe clinical manifestations could potentially be the consequence of PCMV infection.

Effects of adjuvants on the immune response of pigs after intradermal administration of antigen.

The ability of different adjuvants to enhance immune responses to intradermal (ID) immunisation with a model antigen was studied in pigs. Immune responses were evaluated with respect to the intensity of systemic and mucosal antibody formation, their isotype characterisation and rate of cell-mediated immunity. These findings were compared with the intensity of adverse local reactions. Six groups of piglets were immunised with keyhole limpet haemocyanin (KLH) antigen alone or in combination with aluminium hydroxide or selected oil-based adjuvants (complete and incomplete Freund's adjuvants, Montanide ISA 206 and Emulsigen). Systemic specific antibody responses were significantly increased following ID administration of antigen together with any of the adjuvants used. IgG antibody responses were most pronounced after the first administration of antigen, being stimulated with both Freund's and Montanide ISA 206 adjuvants. The oil adjuvants also enhanced the cell-mediated immune responses and the levels of local IgA antibodies in the respiratory mucosa. On the other hand, they elicited more pronounced adverse local reactions.

Changes in lymphocyte function and subsets in dogs with naturally occurring chronic renal failure.

Chronic renal failure (CRF) causes immunosuppresion in humans and is thought to be one of the causes of noninfectious secondary immunosuppression in dogs. Hematological, biochemical, and immunological examinations were performed on blood samples obtained from dogs in various stages of CRF. The number of dogs with lymphopenia increased with the progression of clinical signs. All main subsets of lymphocytes were decreased, but more considerable reduction was detected in B-cells, Tc-cells, and NK cells. Depressed lymphocyte response to concanavalin A and pokeweed mitogen was found in dogs with severe clinical signs and lymphopenia. Our results, showing impaired immunological functions, are similar to results obtained from uremic humans, suggesting that infection may be an important complication in dogs with CRF.

The structure and functional analysis of canine T-cell receptor beta region.

VDJ recombination is a key process in T-cell receptor (TCR) and immunoglobulin (Ig) molecules development. Comparison of ENSEMBL and GenBank database information revealed major differences in dog T-cell receptor beta (TRB) region annotations. ENSEMBL based genomic alignment of dog TRB sequence with human sequence and annotation showed a very similar structure of TRB. However, there is only one cluster of DJC segments in dogs. In dog, 38 V segments are followed by 1 D segment, 6 J segments and 1 C segment. Like humans and mice, dogs have another V segment opposite in orientation downstream of the C segment. V segments anticipated were analyzed using the RT-PCR and capillary electrophoresis. Thirty-one of them were identified in samples of thymus and spleen RNA and thus believed to be subjected to chromosomal rearrangement and RNA splicing. We identified and analyzed probable structure of canine TCR beta region, which is different when compared to sequences published in GenBank or ENSEMBL databases.

Selected markers of cardiovascular disease in a population exposed to arsenic from drinking water.

This study examined prevalence and serum levels of selected markers of cardiovascular disease in 34 subjects from a Croatian rural population exposed to high levels of arsenic (As) from drinking water (611.89±10.06µg/l). The prevalences of overweight and obese subjects in the population were 32% and 35%. Half the subjects had hypertension, 29% had increased fasting serum glucose level and two were diabetic. Median total cholesterol (5.82mmol/l) and triglycerides (2.15mmol/l) were above the desirable margins. The median C-reactive protein level (1.20mg/l) was slightly higher than previously reported for healthy subjects. Serum Hsp70 level was significantly higher in nonsmokers. Total urinary As levels were positively correlated with age-adjusted serum levels of cobalamin. Near significance were also serum total bilirubin, antibodies to Hsp60 and folate. Tentative investigation of risk factors among subjects classified by tumor necrosis factor-α -308G/A and interleukin-6-174G/C gene polymorphisms was also performed. Collectively, the results are in agreement with the hypothesis of As-induced and/or compounded cardiovascular disease.

Flow cytometric analysis of bone marrow leukocytes in neonatal dogs.

Dogs represent both an important veterinary species and a convenient model for allogeneic hematopoietic stem cell transplantation. Even though anti-canine CD34 antibodies have recently become available, little is known about hematopoietic lineages in dogs, partially because CD34- cells have been ignored in all analyses performed so far. In this study, we have focused on the bone marrow mononuclear compartment to provide an additional piece of information on the phenotype of CD34+ progenitors and to identify the dominant CD34- population. We have shown that, in contrast to the adults, mature lymphocytes are scarce in neonatal dog bone marrow. Using cross-reactive antibodies against CD79alpha we have shown that the B lineage of hematopoiesis strongly prevails. CD34+ cells were shown to be positive for MHC class II and SWC3, a member of the signal regulatory protein family.