Mechanism of Protection During the Early Phase of a Generalized Viral Infection. I. Contribution of Phagocytes to Protection against Ectromelia Virus

Abstract
Effects of carrageenan and γ-irradiation on virus titre in the liver were observed after intravenous inoculation of 8 × 103 p.f.u. of ectromelia virus which was not lethal for untreated mice. Trapping of virus by the liver within 30 min and an initial transient reduction in titre by day 1 were not affected by γ-irradiation but were inhibited by pretreatment with carrageenan. An increase from day 1 to day 3 was not affected by γ-irradiation but was augmented by pretreatment with carrageenan. Therefore, protection within 3 days may depend principally upon carrageenan-sensitive and irradiation-resistant cells, namely, fixed macrophages. Elimination of virus from day 4 to day 7 depended upon cell-mediated immunity. When carrageenan was given 3 days after virus inoculation, the titre of virus increased progressively from day 4 ultimately to kill the hosts. The cytotoxic activity of spleen cells against infected target cells was raised in carrageenan-treated mice as well as in untreated mice. Immune elimination of virus may be mediated by a mechanism requiring the cooperation of sensitized T lymphocytes and blood monocytes.

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