Immunopathogenesis of classical swine fever: role of monocytic cells.
Virulent classical swine fever (CSF) represents an immunomodulatory viral infection that perturbs immune functions. Circulatory and immunopathological disorders include leukopenia, immunosuppression and haemorrhage. Monocytic cells - targets for CSF virus (CSFV) infection - could play critical roles in the immunopathology, owing to their production of immunomodulatory and vasoactive factors. Monocytes and macrophages (Mphi) are susceptible to virus infection, as a consequence of which prostaglandin E2 (PGE2) production is enhanced. The presence of PGE2 in serum from CSFV-infected pigs correlated with elevated PGE2 productivity by the peripheral blood mononuclear cells from these same animals. It was noted that these PGE2-containing preparations did not inhibit, but actually enhanced, lymphocyte proliferation. The proinflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6 were not involved, although elevated IL-1 production could relate to lymphocyte activation. Nevertheless, IL-1 was not the sole element: infected Mphi produced lympho-stimulatory activity but little IL-1. This release of immunomodulatory factors, following CSFV infection of monocytic cells, was compared with other characteristics of the disease. Therein, PGE2 and IL-1 production was noted to coincide with the onset of fever and the coagulation disorders typical of CSF. Consequently, these factors are of greater relevance to the haemorrhagic disturbances, such as petechia and infarction, rather than the leukopenia found in CSF. (+info)
Classical swine fever in Sardinia: epidemiology of recent outbreaks.
A variable region of the gene encoding the major glycoprotein (E2) of Classical Swine Fever Virus (CSFV) was sequenced from 12 Sardinian isolates which had been obtained from three geographically distinct regions of the Island. Phylogenetic analysis of these viruses and others characterized in previous studies [1, 2] indicated that (a) the Sardinian viruses were all members of the common European subgroup 2.3 and were clearly distinct from live vaccines recently used in this area; (b) they could be resolved into four distinct groups in accordance with the region or date of isolation; (c) in at least two regions wild boar/domestic swine contact was implicated in virus spread; (d) the oldest isolate (1983) and some of the recent isolates were possibly introduced from mainland Italy. In addition, this study has wider implications for the interpretation of CSFV variation. We have been able to demonstrate that small variations within this region of the virus genome (possibly less than 2.7% or five nucleotide substitutions) can be used to separate isolates into groups that precisely fit their geographical distribution. This finding is especially important for deducing the epidemiological relationships between multiple outbreaks caused by similar viruses that occur in close proximity. (+info)
Pathogenesis of granulocytopenia and bone marrow atrophy during classical swine fever involves apoptosis and necrosis of uninfected cells.
Granulocytopenia, a hematological hallmark of classical swine fever, is partially responsible for the suppression of innate immune defenses during classical swine fever. The present report demonstrates that this depletion was apparent as early as 3 days postinfection (p.i.). Both mature peripheral and bone marrow neutrophils were affected, whereas immature neutrophils increased absolutely in the periphery and coincidentally immature myeloid progenitors in the bone marrow. These data suggest that a pathogenic relationship exists between these compartments. The central event was not the arrest of hematopoietic cell proliferation or of the mobilization process, but instead apoptosis and possibly also necrosis were shown to play a role. This increase in apoptotic and dead cells was detected as early as 1-3 days p.i. In contrast, viral RNA in bone marrow hematopoietic cells (BMHC) was first detected 5 days p.i., and significant amounts of infected BMHC were detected only 7 days p.i., with the major target being the myeloid compartment. The increased caspase-3 activity observed supported a role for apoptotic cell death. Furthermore, the elevated caspase-9 activity indicated the involvement of the mitochondrial apoptotic pathway. Taken together, the results demonstrate that granulocytopenia and bone marrow atrophy are mediated by hematopoietic cell death and that indirect virus-host-mediated mechanisms are likely to be responsible. (+info)
Ultrastructural glomerular changes in experimental infection with the classical swine fever virus.
Ultrastructural studies of glomerular changes were performed on 16 pigs experimentally infected with a highly virulent strain of the classical swine fever virus. Our observations revealed the thickening of glomerular basement membranes, swelling of endothelial cells and cytoplasmic vacuolization within podocytes containing abundant viral particles. An early viral infection of podocytes was suggested as the cause of selective swelling of the foot processes of these cells with the consequent obliteration of the glomerular urinary spaces. To our knowledge this is the first report of ultrastructural evidence of classical swine fever virions infecting glomerular podocytes. (+info)
Comparative immunohistopathology in pigs infected with highly virulent or less virulent strains of hog cholera virus.
Eight pigs were inoculated subcutaneously with a highly virulent hog cholera virus (HCV) strain ALD. The infected pigs developed severe illness and became moribund on postinoculation day (PID) 7 or PID 10. Histologic lesions were characterized by severe generalized vasculitis, necrosis of lymphocytes, and encephalitis. HCV antigen was detected in crypt tonsilar epithelial cells, macrophages, and reticular endothelial cells of lymphoid tissues. Antigen localization corresponded well with histologic lesions. Five pigs were inoculated with less virulent HCV Kanagawa/74 strain and were euthanatized on PID 30. All five infected pigs recovered from the illness but became stunted. They also had a slight follicular depletion of lymphocytes, histiocytic hyperplasia, and hematopoiesis in the spleen. Less virulent HCV antigen was observed in the tonsils, kidneys, pancreas, adrenal glands, and lungs. Although antigen localization was less associated with histologic lesions, immunoreactivity was stronger than that in the pigs infected with the ALD strain of HCV. An almost complete loss of B lymphocytes was recognized in pigs infected with the ALD strain and was correlated with follicular necrosis in lymphoid tissues. Loss of B lymphocytes was not prominent in the pigs infected with Kanagawa/74 strain. The number of CD4+ and CD8+ T lymphocytes was significantly higher than that in the noninfected control pigs. (+info)
Application of competitive enzyme-linked immunosorbent assay for the serologic diagnosis of classical swine fever virus infection.
A competitive enzyme-linked immunosorbent assay (C-ELISA), based on a truncated E2 recombinant protein of the Alfort/187 strain of classical swine fever virus (CSFV) and a specific monoclonal antibody M1669, was evaluated using 2,000 sera from clinically healthy pigs in Canada (a CSFV-free country) and sera from experimentally infected pigs. The relative specificity and sensitivity of the C-ELISA were 100% and 86%, respectively, at a cutoff of 25% inhibition using negative and positive pig sera, as defined by the neutralizing peroxidase-linked assay (NPLA). A kappa value of 0.91 was obtained, indicating an excellent level of agreement between the NPLA and the C-ELISA. When sera from 120 infected pigs were used in the test at > or = 21 days postinfection, the sensitivity of the C-ELISA and the kappa value increased to 97% and 0.98, respectively. This C-ELISA will be useful when a large number of samples must be tested, as could occur during a disease outbreak or for surveillance or prevalence studies. (+info)
Characterization of classical swine fever virus associated with defective interfering particles containing a cytopathogenic subgenomic RNA isolated from wild boar.
Classical swine fever virus (CSFV) strain WB82, isolated from a wild boar in 1982, induced a distinct cytopathic effect (CPE) in primary swine testicle cell culture and in most of the porcine cell lines. This strain of CSFV was found to be composed of two biotypes. cytopathogenic (cp) CSFV, as a minor population, and noncytopathogenic (noncp) CSFV, as a major population. The noncp CSFV (designated strain WB82/E+) was obtained by biological cloning, and it showed the exaltation of Newcastle disease virus phenomenon. In Northern blot analysis and RT-PCR assay, CSFV RNA with a subgenomic (sg) length was detected in addition to full-length viral RNA only in the cells in which a CPE had been revealed. These RNAs represent the genomes of typical defective interfering (DI) particles because of the strict dependence on a complementing helper virus and interference with replication of the helper virus. The sg RNA, which exhibits the genomes of the DI particles, lacked the nucleotides of the viral genomic region from Npro to NS2 (4764 bases). When extracted sg RNA was transfected to the cells infected with the WB82/E+ strain, a distinct CPE was observed. Interestingly, the CPE was observed in cells infected with other heterologous noncp CSFV ALD and GPE- strains by sg RNA transfection. The results suggested that these noncp CSFVs act as helper viruses for the replication of sg RNA (DI particles). It was also shown that the cytopathogenicity of strain WB82 is caused by apoptosis. (+info)
Lipopolysaccharide and phorbol 12-myristate 13-acetate both impair monocyte differentiation, relating cellular function to virus susceptibility.
Both lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA) impeded monocyte to macrophage differentiation with respect to typical phenotypic modulation and certain phagocyte-related processes. The down-regulation of the porcine monocyte marker SWC1, and up-regulation of the SWC9 macrophage marker were retarded, but not inhibited, as was the differentiation-associated down-regulation of p53 and myeloperoxidase. Despite this clear impairment of macrophage differentiation, not all cellular functions were equally susceptible. Both agents inhibited phagocytosis, but not low-density lipoprotein receptor-associated endocytosis. Only LPS inhibited tartrate-resistant acid phosphatase up-regulation. In contrast, increase of vacuolar acidification rates was more susceptible to PMA. The activity of certain endosomal/lysosomal enzymes - esterase, nucleotidase, peroxidase and cathepsins - was generally enhanced by both LPS and PMA. This contrasted with autophagosomal activity, detected through the induction of an antiviral state. Disruption of autophagosomes and lysosomes (methionine-O-methyl ester), but not lysosomes alone (glycyl-L-phenylalanine) reversed LPS-induced inhibition of virus replication, without influencing the PMA-induced antiviral effect. Thus, PMA is similar to LPS in inhibiting monocyte to macrophage differentiation, when primary blood monocytes are employed, but not all pathways are equally susceptible. The analyses demonstrate that the pathways modulated during monocyte differentiation function somewhat independently. Moreover, certain functions of monocytic cells are more important with respect to the outcome of virus infection, with autophagosomal activities in particular favouring cell survival. (+info)