Studies on mouse Moloney virus induced tumours: II. Detection of p30 in the serum of mice with Moloney leukaemia by in vitro blocking of complement dependent antibody mediated cytotoxicity.

Sera from Balb/c mice bearing Moloney leukaemia block complement dependent antibody mediated cytotoxicity of an antiserum prepared in rats against syngeneic Moloney virus induced lymphomata when either spleen cells from mice bearing Moloney leukaemia (M) or an in vitro line of Moloney virus transformed cells (MSC) are used as targets. This antiserum has been shown to recognize p30, the major internal virion protein, as a cytotoxic target on these cells. Viral particles were identified by electron microscopic examination of pelleted material obtained from leukaemic sera after high speed centrifugation. However, removal of virus did not affect the capacity of the leukaemic sera to absorb cytotoxicity of rat ILR-3 for MSC targets, and only depressed somewhat its ability to absorb activity of the same antisera against M targets. Virus-free leukaemic sera also blocks complement dependent antibody mediated cytotoxicity of an antiserum prepared in goats against the gs3 determinant of p30. This indicates that the material in leukaemic sera responsible for the in vitro block of antibody mediated cytotoxicity was p30. A lesser degree of block was observed with sera obtained from normal Balb/c mice, but the nature of material responsible is as yet undefined.