Some antigenic relationships of the murine parvoviruses: minute virus of mice, rat virus, and H-1 virus

Humoral immune responses against minute virus of mice vectors

BACKGROUND

Owing to their oncolytic properties, autonomous rodent parvoviruses and derived vectors constitute potential anti-tumor agents.

METHODS

Humoral immune responses to minute virus of mice (MVMp) were characterized. In particular, the generation of neutralizing antibodies on subsequent therapeutic virus applications was evaluated in a mouse melanoma model. Mice bearing subcutaneous melanomas were injected intratumorally with virus and re-injected 10 days later in a second tumor on the other flank. Four days after the first or second injection, the tumors and lymph nodes were analyzed by RT-PCR for gene expression.

RESULTS

Injection of MVMp in tumor-bearing B6 mice resulted in viral gene expression in tumors and draining lymph nodes. A repeated virus administration did not lead to detectable viral transcription if it was preceded by a virus infection 10 days earlier. This protection correlated with the induction of virus-neutralizing antibodies following the first virus application. The restrictions on viral gene expression after a consecutive MVMp injection could be alleviated in subsequent applications by the use of viruses consisting of MVMp genomes packaged into capsids of a related parvovirus. Neutralizing antibody induction was irrespective of the route of administration and of the presence of a tumor and persisted at significant levels at least up to 26 weeks after the viral infection. MVMp infection of B6 mice stimulated the generation of IgM and IgG anti-viral antibodies, the latter mainly of the T-helper (Th) 1-dependent IgG2, and the T-cell-independent IgG3 subclasses.

CONCLUSIONS

Neutralizing antibodies impede the effectiveness of a subsequent virus administration, but can be overcome by pseudotyping.

Viral Disease

This chapter discusses the infections caused by DNA viruses and also RNA viruses. The chapter focuses on the detection, diagnosis, risk assessment, and decision-making regarding viral infections. Several infections caused by DNA viruses are parvoviruses, rat cytomegalovirus, poxviruses, adenovirus, and papovavirus. Several RNA viruses and infections caused by these viruses are coronaviruses, paramyxoviruses, rotavirus and reovirus, and picornaviruses. Monitoring for viral infections should cover at least three venues: animals in established breeding and experimental colonies, animals held in entry quarantine, and animal tissues and products destined for in vivo use. For established colonies, monitoring should be tailored to local conditions. Effective monitoring should encompass sampling on a pre-arranged schedule, which can be intensified if evidence or suspicion of viral infection emerges. Because viral infections of rats can spread insidiously, early detection and epidemiologic “staging” should employ a detection matrix that includes clinical observation, appropriate sampling, and sensitive and specific diagnostic testing.

Infection of peripancreatic lymph nodes but not islets precedes Kilham rat virus-induced diabetes in BB/Wor rats

A parvovirus serologically identified as Kilham rat virus (KRV) reproducibly induces acute type I diabetes in diabetes-resistant BB/Wor rats. The tissue tropism of KRV was investigated by in situ hybridization with a digoxigenin-labelled plasmid DNA probe containing approximately 1.6 kb of the genome of the UMass isolate of KRV. Partial sequencing of the KRV probe revealed high levels of homology to the sequence of minute virus of mice (89%) and to the sequence of H1 (99%), a parvovirus capable of infecting rats and humans. Of the 444 bases sequenced, 440 were shared by H1. KRV mRNA and DNA were readily detected in lymphoid tissues 5 days postinfection but were seldom seen in the pancreas. High levels of viral nucleic acids were observed in the thymus, spleen, and peripancreatic and cervical lymph nodes. The low levels of infection observed in the pancreas involved essentially only endothelial and interstitial cells. Beta cells of the pancreas were not infected with KRV. These findings suggest that widespread infection of peripancreatic and other lymphoid tissues but not pancreatic beta cells by KRV triggers autoimmune diabetes by perturbing the immune system of genetically predisposed BB/Wor rats.

Naturally occurring lethal parvovirus infection of juvenile and young-adult rats

A lethal disease characterized by hemorrhage and necrosis of the brain, testes, and epididymides developed in young adult rats housed in specific pathogen free quarters. Morphological, virological, and serological investigations of the outbreak indicated that the probable causative agent was rat virus (Kilham), a common parvovirus of rats that usually induces persistent, asymptomatic infection in adult rats.

Immunosuppressive activity of a subline of the mouse EL-4 lymphoma. Evidence for minute virus of mice causing the inhibition

Filtered culture fluids from the early in vitro passages of a subline of the C57BL/6 mouse EL-4 lymphoma, EL-4(G-), were strongly inhibitory for BABL/c vs. C57BL/6 mixed lymphocyte cultures (MLC). The inhibitory activity could be preserved by storage at -75 degrees C or 4 degrees C, thus allowing its further characterization. The inhibitory factor was particulate (nondialyzable, sedimentable at 100,000 g for 1 h), very small (recovered after 0.10 mum filtration), sensitive to UV irradiation, but heat stable (56 degrees C, 1 h) and resistant to chloroform. It was infectious, since later, noninhibitory passages of EL-4(G-) tissue culture cells became strongly inhibitory upon inoculation with the culture fluid. This data was consistent with the inhibitory factor being an infectious virus. Virus analysis by mouse antibody production tests revealed that viruses were indeed present in EL-4(G-) ascites cells and in the culture fluid, and not in a late passage of EL-4(G-) tissue culture cells which were not inhibitory. Neutralization of the inhibitory factor was achieved by pretreatment with ascitic fluid or with the sera raised against those (EL-4(G-)-derived materials which contained viruses. Mouse reference immune sera against minute virus of mice (MVM) completely neutralized the inhibitory factor in the culture fluid or in EL-4(G-) ascites cells. Two prototype MVM strains, and one Kilham rat virus preparation, did not inhibit the mouse MLC. Thus, the possibility exists that a variant of MVM, or an unidentified virus, has been grown and selected for in EL-4(G-) cells and recognized, due to its immunosuppressive characteristics. In any event, immunosuppression by EL-4(G-) cells was not mediated by the tumor cells, their metabolic products, or associated endogenous type C viruses, but by an exogenous virus, most likely a variant MVM with immunosuppressive characteristics. This adds weight to a parallel observation from our laboratory on the immunosuppressive effects of Kilham rat virus in rat lymphocyte cultures.