Thymic microenvironment and cultures derived from mouse thymic explants

Summary Cultures derived from thymus fragments of embryonic (18–19 day old), newborn or one month old C57 BL mice have been characterized functionally (phagocytic and nonspecific esterase activities) and morphologically by means of light, scanning (SEM) and transmission (TEM) electron microscopy. The observations show the heterogeneity of the cell populations composing the monolayers. After a few days incubation macrophages appear as the predominating cell type, while epithelial cells usually constitute no more than 30% of the cells. Experiments designed to determine the fate of lymphocytes adhering to the monolayers lead us to believe (on the basis of SEM morphometric analysis) that the survival of lymphocytes attached either to thymic macrophages or to epithelial cells is improved during the first days of coculture. This survival enhancement does not, however, appear to be a specific inductive effect since a similar survival increase is found when lymphocytes adhere to non-thymic cells. In contrast with the monolayer, the expiant provides a three-dimensional culture system able to preserve intact thymic microenvironmental conditions since numerous lymphocytes are found even in five week old cultures which were not overlaid with thymocytes or spleen cells.     

Evaluation of mouse thymic virus antibody detection techniques

Three serologic test methods for detection of serum antibodies to mouse thymic virus (MTV) were compared, including enzyme-linked immunosorbent assay (ELISA), complement fixation (CF) test and indirect fluorescent antibody (IFA) test. Serum was collected at regular intervals from CD-1 mice inoculated intraperitoneally with approximately 200 infectious doses of MTV, and from uninoculated mice placed in cages with the inoculated animals. The inoculated mice became MTV antibody-positive by all three assay methods at 15 days post inoculation, while the cage-contacts were seropositive by all methods at 30 days after contact. Although the incidence of positive results was similar by all methods, titers measured by ELISA were substantially higher than those measured by CF and IFA tests. Because MTV can cause persistent infections that adversely affect the suitability of mice for research, it is recommended that testing for antibodies to this virus be performed routinely.     

Mouse thymic necrosis virus: a novel murine lymphotropic agent

Mouse thymic necrosis virus (TA), one of two naturally occurring herpesviruses in laboratory mice, was first described in 1961. TA has received relatively little attention even though the virus has been isolated independently from various mouse colonies. This neglect is probably due, at least in part, to the lack of suitable cell culture systems. This review summarizes current knowledge concerning thymic necrosis virus, including new results from the author's laboratory. In vivo, TA causes massive thymic necrosis in newborn mice, with temporary ablation of thymocyte precursors for most T lymphocyte classes except T suppressor cells. All strains of laboratory mice appear susceptible. Severe immunosuppression has been demonstrated in acutely infected mice. Most infected animals survive and shed TA chronically from salivary glands and possibly other glandular tissues. In adult mice, primary infection results in persistent salivary gland infection without overt thymic lesions. Infection appears lifelong, with few clinical signs, but possible effects of chronic TA infection on immune function have been studied little. Recent evidence from the author's laboratory suggests that chronic infection may involve T lymphocytes. The name mouse T lymphotropic virus (abbreviation MTLV) is proposed.     

Immunologic effects of neonatal infection with mouse thymic virus.

Mouse thymic virus is a herpesvirus that causes extensive thymic necrosis when given to newborn mice. During the time of acute infection spleen cells have markedly diminished reactivity to T cell phytomitogens and to allogeneic cells and are incapable of effecting a primary in vitro response to a "T-dependent" antigen; responses to B cell mitogens and to a T-independent antigen are unimpaired. Spleens from acutely infected mice have low theta antigen normal numbers of immunoglobulin-bearing cells. Surprisingly, despite widespread necrosis and cellular depletion, thymic cell reactivity to mitogens is unimpaired. However, the ability to thymocytes to proliferate and to generate cytotoxic killer cells in response to allogeneic cells is diminished.     

Murine infection with lymphocytic choriomeningitis virus following gastric inoculation.

Laboratory studies of arenaviruses have been limited to parenteral routes of infection; however, recent epidemiological studies implicate virus ingestion as a natural route of infection. Accordingly, we developed a model for oral and gastric infection with lymphocytic choriomeningitis virus to enable studies of mucosal transmission and vaccination by this additional route.     

Mouse hepatitis virus S in weanling Swiss mice following intranasal inoculation

Three-week-old outbred mice were inoculated intranasally with a mildly pathogenic strain of mouse hepatitis virus (MHV-S). Tissues were analyzed for distribution of infectious virus, lesions, and viral antigen at intervals up to 49 days after inoculation. Sera were tested for neutralizing antibody to MHV-S. Within the first week of infection, virus was isolated from lung and brain of most mice and liver of one mouse, but not from blood, spleen, or intestine. Microscopic lesions consisted of mild olfactory mucosal necrosis, neuronal necrosis of olfactory bulbs and tracts, lymphoplasmacytic infiltrates and vacuolation in the brain, mild nonsuppurative pulmonary perivascular lymphocyte infiltration, focal interstitial pneumonia, and focal necrotizing hepatitis. The presence and distribution of MHV antigen, as determined by indirect immunofluorescence, correlated with virus recovery and acute lesions. No virus or antigen was demonstrable beyond day 7. Serum antibody was first detected on day 10, and titers peaked on day 28 after infection.     

Factors influencing the establishment of Mesocestoides corti in mice following oral inoculation of tetrathyridia

Factors which influence the establishment of tetrathyridia of Mesocestoides corti in mice following inoculation per os were examined. Only a proportion of the tetrathyridia penetrate the gut wall and gain access to the peritoneal cavity and liver, and most of these penetrate through the wall of the small intestine. It appears that tetrathyridia must attach to the intestinal mucosa and commence penetration immediately or they pass into the large intestine and are voided. Establishment was not influenced by strain, sex or age of host. However, the temperature at which tetrathyridia were maintained before inoculation influence their ability to penetrate the intestinal wall. Additionally it appears that tetrathyridia have to undergo a morphological change before or during, this penetration phase.     

Evaluation of immune response to bovine rotavirus following oral and intraperitoneal inoculation in mice

With a view to use mice as an experimental model for studying immune response to bovine rotavirus (BRV), the kinetics of humoral and cellular immune responses to BRV in mice were evaluated by immunizing through intraperitoneal and oral route with UK strain of BRV. Following immunization with BRV, anti-rotavirus antibodies was developed in mice. The mean log antibody titres as measured by ELISA in mice immunized by intraperitoneal route were significantly higher than those immunized by oral route. Significant cellular immune response was observed in BRV-immunized mice on stimulation with BRV antigen, as measured by lymphocyte proliferation assay. The thymidine uptake by splenic and mesenteric lymph-node cells of intraperitoneally immunized mice on stimulation with BRV was 21328 +/- 1225 and 739 +/- 55 CPM, respectively. The splenic cells showed significantly higher stimulation (stimulation index 12.98) as compared to those of mesenteric cells (stimulation index 1.57). Foot pad inoculation test showed maximum virus-specific delayed type hypersensitivity reaction at 24 hr post-challenge following primary immunization and at 18 hr post-challenge following secondary immunization. The results indicate that BRV immunization by intraperitoneal route generates more efficient immune response in mice than by oral route and this route may be used for immune response studies involving BRV infection.