Kenji Machii

Modification of Immune Response in Nude Mice Infected with Mouse Hepatitis Virus

In nude mice experimentally infected with mouse hepatitis virus (MHV), the numbers of early and later plaque forming cells (PFC) to sheep red blood cells (SRBC) generated in the spleen were 7 to 20 times and 2 to 163 times, respectively, greater than those in non‐infected nude mice, when SRBC were given at day 0 to day 21 postinfection. Splenic theta‐positive lymphocytes in infected nude mice were shown to increase only at day 10 or more postinfection. PFC response to bacterial lipopolysaccharide, a T cell‐independent antigen, was not modified in MHV‐infected nude mice.

Acute hepatic failure in IFN-γ-deficient BALB/c mice after murine coronavirus infection

Abstract We previously showed that an intraperitoneal infection with mouse hepatitis virus (MHV) persists in interferon-γ (IFN-γ)-deficient C57BL/6 (B6-GKO) mice and results in subacute fatal peritonitis, which bears a resemblance to feline infectious peritonitis. To examine the role of other host factors in MHV infection in mice, IFN-γ-deficient mice with a BALB/c background (BALB-GKO) were infected intraperitoneally with MHV and compared with B6-GKO mice. In contrast to B6-GKO mice, BALB-GKO mice died within 1 week due to acute hepatic failure. The viral titer of the liver in BALB-GKO mice was significantly higher than that in B6-GKO mice. All hepatocytes in BALB-GKO mice were necrotic at 5 days post-infection, which was clearly distinct from large but limited lesion in the liver from infected B6-GKO mice. The serum alanine aminotransferase activity of infected BALB-GKO mice were higher than that of B6-GKO mice and was paralleled with the severity of the pathological changes and viral titers in infected mice. Administration of exogenous IFN-γ to BALB-GKO partially inhibited the acute death. These results indicate that BALB-GKO and B6-GKO mice clearly show different diseases following MHV infection, although wild type counterparts of both mice apparently showed the same clinical course after MHV infection.

T Cell Subsets Responsible for Clearance of Sendai Virus from Infected Mouse Lungs

T cell subsets responsible for clearance of Sendai virus from mouse lungs determined by adoptive transfer of immune spleen cell fractions to infected nude mice. T cells with antiviral activity developed in spleens by 7 days after intranasal infection. Spleen cell fractions depleted of Lyt‐2+, Lyt‐1+, or L3T4+ cells showed antiviral activity in vivo, although the degree of the activity was lower than that of control whole spleen cells. The antiviral activity of the Lyt‐2+ cell‐depleted fraction was consistently higher than that of L3T4+ (Lyt‐1+)‐depleted cells. In vitro cytotoxic activity against Sendai virus‐associated, syngeneic lipopolysaccharide‐blast cells was detected in stimulated cells from intraperitoneally immunized mice but was lost after depletion of Lyt‐2+ cells. Multiple injection of anti‐Sendai virus antibody into infected nude mice had no effect on lung virus titer. These results indicate that L3T4+ (Lyt‐1+) and Lyt‐2+ subsets are cooperatively responsible for efficient clearance of Sendai virus from the mouse lung.

MHV-Induced Fatal Peritonitis in Mice Lacking IFN-γ

IFN-gamma gene was disrupted by homologous recombination in A3-1 embryonic stem cells. Germinally transmitted chimeric mice were successfully obtained and backcrossed with C57BL/6 (B6) mice 5 or 6 times. Deficiency of IFN-gamma in homozygous mice was confirmed by northern blot analysis of spleen cells stimulated with phorbor esther and calcium ionophore and also by IFN-gamma production in the culture supernatant of spleen cells stimulated with the same reagents. B6 mice lacking IFN-gamma were infected intraperitoneally (ip) with 10(6) PFU of JHMV and monitored for their survival. Approximately 90% of the mice died at 50 days post-infection (pi) and the mean survival time was 28 days. Mice sacrificed at 3 weeks pi showed severe peritonitis accompanying the accumulation of a viscous fluid in the abdominal and thoracic cavities. Microscopically, the disease was characterized by disseminated granulomatous inflammation and exudative fibrinous serositis in the abdominal cavity. Infectious virus was isolated in most tissues including the liver, spleen, kidney, pancreas and lung during the experimental periods. The disease was not observed in wild-type or heterozygous littermates infected i.p. with JHMV. These results suggest that IFN-gamma plays a critical role in MHV infection in mice. This experimental model may provide a unique opportunity to address the pathogenesis of virus-induced peritonitis such as feline infectious peritonitis in cats.

Comparison of Toxicity between Saxitoxin and Decarbamoyl Saxitoxin in the Mouse Bioassay for Paralytic Shellfish Poisoning Toxins

ABSTRACT The mouse bioassay (MBA) for paralytic shellfish poisoning (PSP) toxins has been used in the AOAC Official Method and the official Japanese method. In the AOAC Official Method, the saxitoxin (STX) standard provided by the U.S. Food and Drug Administration (FDA) is used, but no standard is used in the official Japanese method. The objective of this study was to compare the toxicity of decarbamoyl STX (dcSTX), one of the derivatives of STX and a candidate standard for the MBA for PSP toxins in Japan, to that of FDA STX in the MBA platform. In this study, the toxicity of dcSTX was 918.0 ± 44.9 mouse units/µmol, and the relative toxicity ratio of dcSTX to FDA STX based on moles was 0.478.

The Severity of Hepatic Lesion after Intraperitoneal JHMV Infection in IFN-gamma Deficient Mice is Parallel to Viral Replication in Hepatocytes in Vitro

Several factors affect MHV infection in mice (Table 1). They can be classified into two groups, viral factors and host factors. Although JHMV induces a fatal encephalitis in mice after intracerebral infection, it does a mild hepatitis when it is inoculated intraperitoneally. On the other hand, host genetic factor is a critical determinant. Among MHV researchers, it is well known that SJL mice are relatively resistant to intracerebral infection with JHMV (Stohlman & Frelinger 1978). In addition, the immune system is one of the key players that determine MHV infection in mice.

Spontaneous Arthritis in Nude Rats of Rowett Hooded Strain

Spontaneous arthritis was found in 19 of 55 Rowett hooded strain rats with rnu gene. Most cases were in the male rnu/rnu (15/19) but a few occurred in the male rnu/+ (3/10) and female rnu/rnu (1/8). The lesions were first noted as reddened swelling due to exudative inflammation of periarticular soft tissues including synovial membranes in the tarsal and/or carpal joints. Most of the affected animals cured leaving slight induration but in a few male rnu/rnu ankylosis with pannus formation and exostosis developed. No sign of mycoplasmal or bacterial infection was noticed in the colony.