CROSS-PROTECTION MECHANISM BETWEEN SINDBIS AND SEMLIKI FOREST VIRUSES IN MICE

The mode of action and site for cross-protection among Group A arboviruses has been studied in mice using Sindbis and Semliki Forest SF viruses as a working model. Swiss mice immunized with Sindbis virus by the intracerebral route demonstrated substantial resistance to intraperitoneal challenge with lethal doses of SF virus. Serologic examination by hemagglutination inhibition, complement fixation, and neutralization revealed that antibody to SF virus first appeared in the serum of Sindbis-immune and normal mice four days after challenge. SF antibody attained maximum titers in Sindbis-vaccinated mice 10 days after challenge with SF virus and slowly declined thereafter. Antibody responses to SF virus in normal mice paralleled responses found in Sindbis-immune mice, but all normal mice succumbed to SF infection seven days after challenge. Periodic titration of the blood, brain, liver, and spleen in 10- to 14-gram mice showed a detectable quantity of SF virus in the organs of both groups 24 hours after challenge. Maximum titers of SF virus appeared in the blood, liver, and spleen by the third day after challenge.