B lymphocyte activation by coinfection prevents immune control of friend virus infection.

Although the adaptive immune response almost invariably fails to completely eliminate retroviral infections, it can exert significant protection from disease and long-term control of viral replication. Friend virus (FV), a mouse retrovirus, causes persistent infection in all strains of mice and erythroleukaemia in susceptible strains, the course of which can be strongly influenced by both genetic and extrinsic factors. In this study we examine the impact of coinfection on the requirements for immune control of FV infection. We show that congenic C57BL/6 mice, in which the introduction of an allele of the Friend virus susceptibility 2 gene provides the potential for FV-induced leukemia development, effectively resist FV infection, and both T cell- and Ab-dependent mechanisms contribute to their resistance. However, we further demonstrate that coinfection with lactate dehydrogenase-elevating virus (LDV) renders these otherwise immunocompetent mice highly susceptible to FV infection and subsequent disease. The presence of LDV delays induction of FV-specific neutralizing Abs and counteracts the protective contribution of adaptive immunity. Importantly, the disease-enhancing effect of LDV coinfection requires the presence of a polyclonal B cell repertoire and is reproduced by direct polyclonal B cell activation. Thus, immune activation by coinfecting pathogens or their products can contribute to the pathogenicity of retroviral infection.

Lactic dehydrogenase virus infection reduces the expulsion of the nematode Nippostrongylus brasiliensis.

The interleukin (IL)-13-mediated goblet cell response is the major host effector system involved in the expulsion of Nippostrongylus brasiliensis. Lactic dehydrogenase virus (LDV) induced higher levels of N. brasiliensis egg production compared with controls, but the effect of LDV infection on worm expulsion of, and goblet cell and IL-13 responses to, N. brasiliensis have not been studied. In this study, the effects of LDV infection on these host responses against N. brasiliensis were examined. Mice with chronic LDV infection showed significantly lower worm expulsion rates than non-LDV-infected mice after N. brasiliensis infection, and there were no significant differences in the ratio of female versus male adult worms between control and LDV-infected mice. The number of goblet cells in LDV-infected mice was significantly lower than that in controls. In addition, the levels of IL-13 gene expression in lymph nodes were significantly lower in LDV-infected mice compared with controls. These results suggest that LDV infection reduces the protective immune responses against N. brasiliensis infection by the suppression of IL-13 production.

Reduction of serum interferon (IFN)-gamma concentration and lupus development in NZBxNZWF(1)mice by lactic dehydrogenase virus infection.

The complexity of cytokine regulation and the imbalance of helper T (Th)1 and Th2 subsets in systemic lupus erythematosus (SLE) animal models and human SLE are well recognized. In this study in NZBxNZWF(1)mice, the effects of lactic dehydrogenase virus (LDV) infection on the production of interferon (IFN)-gamma in the serum and the development of autoimmune disease were examined. The progress of the disease (the development of glomerulonephritis, formation of glomerular IgG and C3 deposits, increase in the blood urea nitrogen values, and mortality) was parallel with an increase in serum IFN-gamma in uninfected NZBxNZWF(1)mice. These changes were inhibited in LDV-infected NZBxNZWF(1)mice. Our findings suggest that increase in serum IFN-gamma may be associated with the active disease in NZBxNZWF(1)mice.

Diagnosis of equine arteritis virus infection in two horses by using monoclonal antibody immunoperoxidase histochemistry on skin biopsies.

Two 5-year-old grade male horses presented with epiphora, rhinorrhea, conjunctival and nasal mucosal hyperemia, and dorsal and thoracic macropapular rash. Skin biopsies were collected from the affected areas, and serial sections were evaluated following hematoxylin and eosin and immunoperoxidase histochemistry staining by using a murine monoclonal antibody of the immunoglobulin G2A isotype recognizing the 30-kDa membrane protein of equine arteritis virus (EAV). In both horses, lesions consisted of mild to moderate diffuse superficial dermal edema and vasculitis with mild perivascular lymphocytic infiltrates, occasional endothelial hypertrophy, and single-cell necrosis of tunica media myocytes. Immunohistochemically, a few endothelial cells, myocytes, and pericytes containing intracytoplasmic EAV antigen were identified. Immunoperoxidase histochemistry of skin biopsies can be used as an ancillary test for the clinical diagnosis of equine viral arteritis in horses, especially when a cutaneous macropapular rash is evident.

Equine viral arteritis in newborn foals: clinical, pathological, serological, microbiological and immunohistochemical observations.

Clinical, pathological, immunohistochemical, serological and microbiological findings are described for 2 geographically and temporally distinct equine arteritis virus (EAV) epidemics in newborn foals. Outbreak A occurred at a commercial Standardbred breeding facility; Outbreak B began in a group of research animals. Clinical signs were severe and primarily referable to the respiratory tract. Fever and leucopenia and/or thrombocytopenia were observed in foals surviving for more than 24 h. The most common gross pathological findings were limited to the respiratory tract. Common histopathological findings included interstitial pneumonia, lymphocytic arteritis and periarteritis with fibrinoid necrosis of the tunica media. Renal tubular necrosis was noted in 2 foals. Immunoperoxidase histochemistry combined with virus isolation was diagnostic in all cases.

Detection of porcine reproductive and respiratory syndrome virus and Mycoplasma hyorhinis antigens in pulmonary lesions of pigs suffering from respiratory distress.

Eleven field cases of a disease characterized by severe dyspnoea or abdominal breathing were examined post mortem. The affected pigs had antibody against porcine reproductive and respiratory syndrome virus (PRRSV). The predominant lung lesions were severe proliferative and interstitial pneumonia, and slight suppurative bronchopneumonia. The lesions were closely associated with the sites at which PRRSV and Mycoplasma hyorhinis antigens were detected. Four of five pigs inoculated with PRRSV developed slight pneumonitis. The fifth animal, which died of severe pneumonitis, yielded a heavy culture of M. hyorhinis. These findings demonstrate that dual infection with M. hyorhinis and PRRSV caused severe pulmonary lesions.

Porcine reproductive and respiratory syndrome virus does not exacerbate Mycoplasma hyopneumoniae infection in young pigs.

The purpose of this study was to determine if Porcine Reproductive and Respiratory Syndrome (PRRS) virus infection altered the severity of acute Mycoplasma hyopneumoniae (MH) infection in young pigs. Twenty five, 3-week-old male pigs were randomly assigned by litter and weight to one of 3 groups. Groups 1 (PRRS only, n = 5) and 2 (PRRS + MH, n = 10) were inoculated intranasally with PRRS virus (IN-5 isolate, 10(5) TCID50) and viremia in all pigs was confirmed by virus isolation from serum 3 days later. Group 3 (MH only, n = 10) was inoculated at the same time with virus free culture media. Seven days after virus inoculation, Groups 2 and 3 were inoculated intratracheally with MH (strain P-5722-3, 10(7) CCU). All pigs were euthanized and necropsied 28 days later, when maximum lesions of mycoplasmosis occurs. Pigs in group 1 did not cough and had no gross lung lesions, but were still viremic at necropsy. MH was isolated from all pigs in groups 2 (avg. log 5.2 +/- 1.3) and 3 (avg. log 5.1 +/- 1.5), but differences were not significant (P = 0.87). Similarly, there were no differences in average days coughing (8.9 +/- 2.8 v 11.2 +/- 4.5, P = 0.17), grossly pneumonic lung (16.5% v 17%, P = 0.91), or microscopic lung lesion scores (10.1 +/- 2.6 v 11.1 +/- 1.9, P = 0.35) between pigs in groups 2 and 3. Under these experimental conditions, PRRS virus infection did not increase the severity of experimental Mycoplasma hyopneumoniae infection in young pigs.

Mycoplasma hyorhinis infection levels in lungs of piglets with porcine reproductive and respiratory syndrome (PRRS).

The infection levels of Mycoplasma hyorhinis, M. hyopneumoniae and M. hyosynoviae in the lung of piglets were examined in relation to porcine reproductive and respiratory syndrome (PRRS). These animals consisted of 43 PRRS piglets with PRRS, 2 piglets infected with PRRS virus but symptom-free, and 10 control piglets free of PRRS virus and its antibody. M. hyorhinis was isolated from 40 of the 43 PRRS piglets, from 1 of the 2 latent infected piglets and from 3 of the 10 control piglets. The number of M. hyorhinis isolated from the lungs of PRRS piglets was more than 10(5) CFU/g, but those isolated from the latent infected piglets and the control piglets were less than 10(3) CFU/g. In addition to this, Haemophilus parasuis and Pasteurella spp. were frequently isolated from the piglets with PRRS (51.2% and 25.6%, respectively). On the other hand, M. hyopneumoniae was isolated from only 4 of 55 piglets tested, and M. hyosynoviae was not isolated. M. hyorhinis was also detected directly in the lung emulsion samples from almost all the PRRS piglets using a polymerase chain reaction-based method.

Dual infections of feeder pigs with porcine reproductive and respiratory syndrome virus followed by porcine respiratory coronavirus or swine influenza virus: a clinical and virological study.

Dual infections of pigs with porcine reproductive and respiratory syndrome virus (PRRSV) followed by a second common respiratory virus, either porcine respiratory coronavirus (PRCV) or swine influenza virus (SIV), were studied. The aim was to determine if dual infections, as compared to single virus infections, result in enhanced clinical manifestations. It was also examined if PRRSV replication affects replication of PRCV or SIV in the respiratory tract. Groups of conventional 10 week old pigs were inoculated with PRRSV-only (3 pigs), PRCV-only (4 pigs) or SIV-only (4 pigs). Dual inoculations with PRRSV-PRCV (4 pigs) and PRRSV-SIV (3 groups of 4, 4 and 5 pigs) were performed at a 3 day interval. A group of uninoculated control pigs (8 pigs) was included. The infection with PRRSV-only induced a transient fever (40.2 degrees C) at 2 DPI, but no respiratory signs. The PRCV-only infection remained subclinical. The SIV-only infection resulted in a one day fever (40.1 degrees C) with moderate tachypnoea and dyspnoea. Mean weight gain in the virus-inoculated groups was retarded compared with the control group. The PRRSV-PRCV infection induced a 9 day lasting fever (peak 40.9 degrees C) with tachypnoea, dyspnoea and productive coughing. The PRRSV-SIV infection resulted in fever and respiratory signs in all 3 groups. Clinical signs, however, were more pronounced in group 1 than in groups 2 and 3. Pigs of group 1 showed fever during 10 days (peak 41.4 degrees C), tachypnoea, marked dyspnoea with abdominal breathing, and a productive cough. Pigs of groups 2 and 3 had fever for 5 and 3 days (peaks 40.6 and 40.3 degrees C) respectively and mild respiratory disorders. Mean weight gain during 14 DPI of the 2nd virus was 5.9 kg in the PRRSV-PRCV group and 4.0, 6.8 and 6.7 kg in PRRSV-SIV groups 1, 2 and 3 respectively. Mean weight gain during the corresponding period in the PRRSV-only group was 8.6 kg. It was concluded that dual infections with viruses causes more severe disease and growth retardation than single PRRSV infection. PRCV excretion curves were similar in single and dual virus inoculated groups. Excretion of SIV was delayed by 2 days in the dual inoculated pigs. Thus, replication of the second virus is not (PRCV) or only slightly (SIV) affected by a prior infection with PRRSV.

Fetal microscopic lesions in porcine reproductive and respiratory syndrome virus-induced abortion.

Microscopic lesions in four cases of abortion caused by porcine reproductive and respiratory syndrome virus (PRRSV) were characterized by arteritis, myocarditis, and encephalitis. Fetal PRRSV infection was confirmed by virus isolation or immunohistochemistry and serology. Although fetal microscopic lesions in PRRSV abortions are rarely reported, diagnosticians should consider PRRSV when these lesions occur.

Infection of central nervous system cells by ecotropic murine leukemia virus in C58 and AKR mice and in in utero-infected CE/J mice predisposes mice to paralytic infection by lactate dehydrogenase-elevating virus.

Certain mouse strains, such as AKR and C58, which possess N-tropic, ecotropic murine leukemia virus (MuLV) proviruses and are homozygous at the Fv-1n locus are specifically susceptible to paralytic infection (age-dependent poliomyelitis [ADPM]) by lactate dehydrogenase-elevating virus (LDV). Our results provide an explanation for this genetic linkage and directly prove that ecotropic MuLV infection of spinal cord cells is responsible for rendering anterior horn neurons susceptible to cytocidal LDV infection, which is the cause of the paralytic disease. Northern (RNA) blot hybridization of total tissue RNA and in situ hybridization of tissue sections demonstrated that only mice harboring central nervous system (CNS) cells that expressed ecotropic MuLV were susceptible to ADPM. Our evidence indicates that the ecotropic MuLV RNA is transcribed in CNS cells from ecotropic MuLV proviruses that have been acquired by infection with exogenous ecotropic MuLV, probably during embryogenesis, the time when germ line proviruses in AKR and C58 mice first become activated. In young mice, MuLV RNA-containing cells were found exclusively in white-matter tracts and therefore were glial cells. An increase in the ADPM susceptibility of the mice with advancing age correlated with the presence of an increased number of ecotropic MuLV RNA-containing cells in the spinal cords which, in turn, correlated with an increase in the number of unmethylated proviruses in the DNA extracted from spinal cords. Studies with AKXD recombinant inbred strains showed that possession of a single replication-competent ecotropic MuLV provirus (emv-11) by Fv-1n/n mice was sufficient to result in ecotropic MuLV infection of CNS cells and ADPM susceptibility. In contrast, no ecotropic MuLV RNA-positive cells were present in the CNSs of mice carrying defective ecotropic MuLV proviruses (emv-3 or emv-13) or in which ecotropic MuLV replication was blocked by the Fv-1n/b or Fv-1b/b phenotype. Such mice were resistant to paralytic LDV infection. In utero infection of CE/J mice, which are devoid of any endogenous ecotropic MuLVs, with the infectious clone of emv-11 (AKR-623) resulted in the infection of CNS cells, and the mice became ADPM susceptible, whereas littermates that had not become infected with ecotropic MuLV remained ADPM resistant.

Suppression of development of glomerulonephritis in NZB x NZWF1 mice by persistent infection with lactic dehydrogenase virus: relations between intercellular adhesion molecule-1 expression on endothelial cells and leucocyte accumulation in glomeruli.

The development of glomerulonephritis (GN) in autoimmune NZB x NZWF1 mice was suppressed by persistent lactic dehydrogenase virus (LDV) infection. In this study the expression of intercellular adhesion molecule-1 (ICAM-1) on endothelial cells in glomeruli was examined during the development of GN. ICAM-1 expression on endothelial cells preceded the accumulation of leucocytes within glomeruli. The uninfected mice exhibited an age-related and profound increase in ICAM-1 expression associated with the development of a GN as evidenced by deposits of IgG and C3. Uninfected mice also showed increased accumulation of leucocytes, such as polymorphonuclear leucocytes (PMNs), macrophages, T and CD4+ cells, which express the lymphocyte function-associated antigen-1 (LFA-1) within glomeruli during the development of GN. These changes were strongly suppressed by LDV infection. Our findings suggest that the expression of ICAM-1 in glomerular endothelial cells may, at least in part, contribute to the development of GN. Suppressed expression of ICAM-1 in LDV-infected mice may be responsible for the suppression of GN seen in these animals. Thus there may be a pathogenetic role for ICAM-1 expression and for intraglomerular accumulation of leucocytes, especially PMNs, which express LFA-1 in the development of GN.

Effect of infection by lactic dehydrogenase virus on expression of intercellular adhesion molecule-1 on vascular endothelial cells of pancreatic islets in streptozotocin-induced insulitis of CD-1 mice.

Streptozotocin (SZ)-induced insulitis, which is an animal model for insulin-dependent diabetes mellitus, was suppressed by lactic dehydrogenase virus (LDV) infection. There were no differences in degenerative and necrotic changes of islet cells between SZ-treated mice and SZ-treated mice with LDV infection during the pre-insulitis phase. The degree of insulitis was more severe and the plasma glucose levels were higher in SZ-treated mice than in SZ-treated mice with LDV infection. Severe degenerative and necrotic changes of cells with mononuclear cell infiltration into the islets were seen in the SZ-treated mice. Infiltration of these cells into islets was less in SZ-treated mice with LDV infection. During the pre-insulitis phase, there was slight expression of intercellular adhesion molecule-1 (ICAM-1) on the surface of vascular endothelial cells in and/or around islets in both groups. ICAM-1 expression on vascular endothelial cells increased in parallel to the degree of insulitis. The degree of this expression in SZ-treated mice was higher than in SZ-treated mice with LDV infection. These results suggest that expression of ICAM-1 on vascular endothelial cells in SZ-treated mice may be important for the development of insulitis. Also, decreased expression of ICAM-1 in the islets may be responsible for the inhibition of the development of insulitis seen in SZ-treated mice with LDV infection.

Serological studies on the potential synergism of porcine reproductive and respiratory syndrome virus and influenza-, corona- and paramyxoviruses in the induction of respiratory symptoms in swine.

Sera from 265 finishing pigs belonging to 70 herds, in which severe respiratory disorders were observed, were examined for antibody prevalence to porcine reproductive and respiratory syndrome virus (PRRSV), influenza virus subtypes H3N2 and H1N1, porcine respiratory corona virus (PRCV) and a recently described porcine paramyxovirus (PPMV). By immunoperoxidase-monolayer assay 69.1% of these sera were positive for PRRSV. Hemagglutination inhibiting activity was found in 55.1% of the sera for influenza virus subtype H1N1 (strain A/swine/Arnsberg/1/81). in 51.3% for influenza virus subtype H3N2 (strain A/Hong Kong/1/68) and in 14.3% for PPMV. PRCV specific antibodies, as determined by differential competitive blocking enzyme-linked immunosorbent assay were demonstrated in 192 of 236 (81.3%) sera. In order to reveal associations interspecific coefficients were calculated for antibody prevalence between PRRSV and the other viruses. Positive associations to PRRSV titres were found to PRCV, PPMV and influenza virus subtype H1N1 titres. chi-square analysis showed the statistical significance of associations regarding PRCV and influenza virus subtype H1N1. Depletion of lung macrophages after PRRSV infection is discussed as a possible mechanism for the promotion of secondary infections.