Host Cell Modification of Lymphocytic Choriomeningitis Virus and Newcastle Disease Virus Altering Viral Inactivation by Human Complement

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Abstract
Complement in human serum inactivated several enveloped viruses, but for some viruses the degree of inactivation depended on their passage history. In short, human serum detected cell-induced modifications of virions. Normal human serum, lacking detectable neutralizing antibodies to the virions, inactivated lymphocytic choriomeningitis virus (LCMV) and Newcastle disease virus (NDV) when the viruses were passed through some cell lines but not others. Host cell modification was further documented with LCMV since antibody to the cell (in conjunction with a complement source) inactivated virus produced by that cell. The mechanism by which human serum inactivated LCMV passed through L cells was determined. By using serum immunochemically depleted in the classical complement pathway component C4 and/or the alternative complement pathway component factor B, as well as other methods, it was shown that LCMV was inactivated via the classical complement pathway. Absorption and immune precipitation experiments indicated that the inactivation of LCMV by complement was mediated by natural antibody directed against the host (L-929) cell. NDV grown in chick embryo cells could be inactivated by either complement pathway in the absence of the other. A requirement for antibody could not be demonstrated in the NDV system. On the basis of these data it is proposed that alterations in virulence dependent upon passage of the virus in cells or animals may be partially explained by changes in virus sensitivity to human serum inactivation.