Rabbit hyperimmune antisera against Sindbis (SIN) or Semliki Forest (SF) virus were absorbed with purified SIN virus or SIN virus-infected cells, or with SF virus or SF virus-infected cells. Residual antibody titers were determined by hemagglutination inhibition (HAI) and antibody-dependent, complement-mediated cytolysis (ADCMC) assays. It appeared that absorption with virus-infected cells removed ADCMC-detectable cross-reactive antibody much more efficiently than did absorption with either

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... s. HAI assays with the same absorbed antisera indicated that both virus and virus-infected cells removed HAI-detectable crossreactive antibody. On the basis of these and other data, there appeared to be a cross-reactive antigen present on virus-infected cells which was detectable by ADCMC and was distinct from the cross-reactive antigen assayed by HAI. on May 9, 2020 by guest http://iai.asm.org/ Downloaded from