The capacity of monoclonal antibodies to protect mice passively against yellow fever (YF) virus infection was investigated. Both neutralizing (54K-specific) and non-neutralizing (54K- and 48K-specific) antibodies protected mice against challenge with the RMP substrain of YF virus. Average survival times of mice inoculated intracerebrally with a standard lethal dose of YF virus differed according to the strain used: thus mice inoculated with the most neurovirulent viruses, FNV and Asibi, survived for 6.50 and 7.65 days respectively, and those with RMP virus survived for 15.75 days. The capacity of antibodies to protect mice passively against virus challenge was directly related to virus neurovirulence. Possible mechanisms and the significance of protection by antibodies against non-structural proteins that do not mediate neutralization, are discussed.
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