Cross‐reactive and type‐specific complement‐fixing structures of oriboca virions

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Abstract
Characteristics of two components of Oriboca virus were studied after they were separated and semipurified by velocity centrifugation. A component of low infectivity and broad cross‐reactivity in the complement‐fixation (CF) test had a sedimentation coefficient of 6–7S. Infectious Oriboca virions with hemagglutinating (HA) activity had a sedimentation coefficient of 457S. These virions cross‐reacted broadly with Murutucu viral antibody. The crossreactive, virion‐associated component and a type‐specific CF fragment were released from virions by disruption with Nonidet P‐40. These CF fragments separated by sucrose gradient equilibrium centrifugation had densities of 1.245 gm/ml and 1.181 gm/ml, respectively, and were both interpreted to be envelope structures. The type‐specific CF antigen appeared to be related to the viral hemagglutinin in that it blocked hemagglutination‐in‐hibiting (HI) antibody, whereas the cross‐reactive CF fragment did not.