In vivo Junin virus-mouse macrophages interaction.

The role of mononuclear phagocytic cells in extraneural infection of the mouse with Junin virus (JV) was studied. Endpoint susceptibility (4 days of life) was evaluated by intraperitoneal (i.p.) inoculation of suckling mice. By means of immunofluorescence (IF) and C3 receptor assays, it was found that macrophages were permissive to viral replication in vivo and fostered the recruitment of inflammatory cells as evidenced by the absence of C3 marker. In support, in vitro infection failed to induce alterations of this receptor. Throughout, both in vivo and in vitro, there were no signs of C3-mediated phagocytosis. Silica treatment had no effect on either resistance or susceptibility, suggesting that the "macrophage-barrier" failed to hinder or favour the course of disease. Differences with other JV models are discussed.

Effect of staggered cyclophosphamide-immunosuppression on resistance to experimental Junin virus infection.

Otherwise resistant adult mice were rendered susceptible to intracerebral Junin virus (JV) infection only when a staggered cyclophosphamide (CY) schedule was used. Forty-five-day old Balb/c mice, intracerebrally JV-infected and immunosuppressed with four 50 mg/kg body weight CY doses at days -1, +1, +4, +6 (day 0: viral infection) developed a lethal disease (86.6 per cent mortality) with high CNS viral titers and brain lesions. Neutralizing antibodies were absent throughout, while immunofluorescent antibody levels were considerably diminished. The transfer of hyperimmune serum conferred partial though significant protection on CY-treated animals but no correlation was found between CNS viral titers and mortality since in both infected CY-treated and untreated mice similar brain viral content was found. This was also confirmed by immune spleen cell transfer at day 0 where the clearance achieved was unable to modify the time course of the disease. Feasible mechanisms explaining recovery from JV infection by means of the protective effect of antibodies and the cell-mediated clearance are discussed.

[Effect of various schedules of cyclophosphamide administration on the mortality of the adult mouse infected with Junín virus]. / Efecto de distintos esquemas de administración de ciclofosfamida en la mortalidad del ratón adulto infectado con virus Junín.

The object of this paper was to determine the influence of cyclophosphamide immunosuppression on the mortality of 40-45 day old Balb/c mice infected intracerebrally with a pathogenic strain of Junin virus, using different administration schedules. Up to 200 mg/kg of cyclophosphamide were not toxic. Results show that, unlike in other experimental models, three or four 50 mg/kg cyclophosphamide doses given both before and after viral infection were required to break-down resistance to Junin virus (90-96.5% mortality vs. 8% in controls). Taking into account the effect of cyclophosphamide on the cell populations involved in the immune response, causes likely to lead to the greater susceptibility of the suppressed adult mouse to Junin virus are discussed.

[Variations of the delayed hypersensitivity reaction in mice inoculated with different lots of sheep red blood cells]. / Variaciones de la reacción de hipersensibilidad retardada en ratones inoculados con diferentes lotes de glóbulos rojos de carnero.

Delayed-type-hypersensitivity (DTH) response "in vivo" is commonly evaluated by the footpad swelling test (FPST). High doses of Sheep Red Blood Cells (SRBC) are known to produce negligible DTH, while low doses lead to optimal sensitization. As expected FPST values obtained in Balb/c mice using 10(6) or 10(8) SRBC as sensitizing doses, showed that in 9 out of 10 batches from individual rams, the former dose resulted in higher values than the latter. However, only 3 out of the above 9 exhibited statistically significant differences between immunizing doses (Table 1). Therefore, in our hands, the accuracy of FPST is highly dependent on the SRBC source. We suggest the need of testing individual SRBC batches at both dilutions before use.

Variaciones de la reacción de hipersensibilidad retardada en ratones inoculados con diferentes lotes de glóbulos rojos de carnero. / [Variations of the delayed hypersensitivity reaction in mice inoculated with different lots of sheep red blood cells]

Delayed-type-hypersensitivity (DTH) response [quot ]in vivo[quot ] is commonly evaluated by the footpad swelling test (FPST). High doses of Sheep Red Blood Cells (SRBC) are known to produce negligible DTH, while low doses lead to optimal sensitization. As expected FPST values obtained in Balb/c mice using 10(6) or 10(8) SRBC as sensitizing doses, showed that in 9 out of 10 batches from individual rams, the former dose resulted in higher values than the latter. However, only 3 out of the above 9 exhibited statistically significant differences between immunizing doses (Table 1). Therefore, in our hands, the accuracy of FPST is highly dependent on the SRBC source. We suggest the need of testing individual SRBC batches at both dilutions before use.

Efecto de distintos esquemas de administración de ciclofosfamida en la mortalidad del ratón adulto infectado con virus Junín. / [Effect of various schedules of cyclophosphamide administration on the mortality of the adult mouse infected with Junín virus]

The object of this paper was to determine the influence of cyclophosphamide immunosuppression on the mortality of 40-45 day old Balb/c mice infected intracerebrally with a pathogenic strain of Junin virus, using different administration schedules. Up to 200 mg/kg of cyclophosphamide were not toxic. Results show that, unlike in other experimental models, three or four 50 mg/kg cyclophosphamide doses given both before and after viral infection were required to break-down resistance to Junin virus (90-96.5

mortality vs. 8

in controls). Taking into account the effect of cyclophosphamide on the cell populations involved in the immune response, causes likely to lead to the greater susceptibility of the suppressed adult mouse to Junin virus are discussed.

Efecto de distintos esquemas de administración de ciclofosfamida en la mortalidad del ratón adulto infectado con virus Junín / [Effect of various schedules of cyclophosphamide administration on the mortality of the adult mouse infected with Junín virus]

The object of this paper was to determine the influence of cyclophosphamide immunosuppression on the mortality of 40-45 day old Balb/c mice infected intracerebrally with a pathogenic strain of Junin virus, using different administration schedules. Up to 200 mg/kg of cyclophosphamide were not toxic. Results show that, unlike in other experimental models, three or four 50 mg/kg cyclophosphamide doses given both before and after viral infection were required to break-down resistance to Junin virus (90-96.5

in controls). Taking into account the effect of cyclophosphamide on the cell populations involved in the immune response, causes likely to lead to the greater susceptibility of the suppressed adult mouse to Junin virus are discussed.

Effect of fractional cyclophosphamide dosage on sheep red blood cell-delayed-type hypersensitivity response in mice.

The CY-enhancing effect on DTH response of mice against SRBC was studied by administering to sensitized animals graded amounts of drug at various times during the immune response. The use of a staggered schedule for CY administration made it clear that this enhancing effect could be augmented even further by lowering the standard 200 mg/kg CY dose. Animals immunized on day 0 with 1 X 10(8) SRBC receiving 50 mg/kg doses on days -1, +1, and +4 showed higher DTH responses on day +7 than those similarly sensitized 1 day after the administration of 200 mg/kg body weight. In addition, we wanted to demonstrate that the TDTH effector cell is sensitive to CY in vivo, because a single 50 mg/kg dose inoculated on day +6 can lower by 50% an already established DTH response. This effect was not due to an effect of CY treatment on bone marrow-derived cells recruited to DTH responses; inhibition of DTH responses were transferred with spleen cells of CY-treated recipients. The action of CY is not dose-dependent; the administration on day +6 of a single dose of 200 mg/kg results in no further depression of the DTH reaction. We conclude that CY affects not only T supp cells, but also cell type(s) involved in the cell-mediated response of mice against SRBC, and that the DTH-enhancing effect of the drug is a blend of its action upon all these cells.

Development of specific immune response in mice infected with Junin virus.

Different parameters of specific immune response involved in the resistance to intracerebral Junin virus (JV) infection were studied in adult BALB/c mice. The relationship of virus replication to production of antiviral antibodies, to occurrence of cytotoxic T cells and to development of delayed-type hypersensitivity response was evaluated. Spleen cytotoxic T cells were assayed by 51Cr-release method on virus-infected H2 compatible targets. Effector T cells were detected on day 2, reached peak concentrations by day 6 and declined on day 10. These cells seemed responsible, at least in part, for virus clearance from the infected target organ, since virus could not be recovered from the brain in any sample taken on days 2, 5, 6, 8, 10, 15 and 20 post infection (p.i.). All three main antibody classes common in viral infection were present. Serum antibodies appeared later than the T cell cytotoxic response. Neutralizing antibodies and those detected by immunofluorescence prevailed in the IgG fraction, whereas the IgM antibody class was reactive in complement fixation assay. Challenge of infected mice with JV did not result in production of delayed-type hypersensitivity as measured by footpad swelling irrespective of the route of sensitization. The possible interpretations of these findings are discussed in connection with the resistance of adult mice to JV infection.