Junin virus multiplication in thymectomized mice. Effect of thymus and immunocompetent cells grafting.

Abstract

Protective effect of thymeetomy performed during 24 hours after birth is verified by inoculation of Balb/c and Rockland mice with 1000 LD50 of Junin virus (RC strain). When thymectomy is performed at 48–72 hours after birth the effect decreased or disappeared. Inoculation on the 8th day with 6×106 spleen cells from immune mice inhibits the thymectomy effect on infected mice. On the contrary, inoculation at the same time with normal or immune mice sera, or with 6×106 spleen cells from normal mice is inefficient to counteract the effects of thymectomy. Isologous thymus grafting performed two hours after thymectomy caused death with neurological symptomatology in 71% of mice infected with Jumn virus, while grafting with 5 isologous thymus 8 days after infection in thymectomized newborn mice has no such effect. Complement fixation and neutralization tests were always negative in thymectomized infected mice until 50 days and in unthymectomized infected mice until 13 days. Similar increases of virus titers in brain are observed in infected thymectomized and unthymectomized mice, reaching a maximum (107 TCID50) 11 days after infection; but on the 50th day the virus titer in thymectomized mice decreases by about 3 log units. The histopathological study of infected unthymectomized mice brain shows intense inflammatory phenomena at vascular level with infiltration of mononucleated cells. This inflammatory reaction is of low intensity or absent in the brain of thymectomized infected mice.