Detection of simian virus 40 T-antigen-related antigens by a 125I-protein A-binding assay and by immunofluorescence microscopy on the surface of SV40-transformed monolayer cells.

Simian virus 40 (SV40)-transformed cells express the SV40-specific tumour transplantation antigen (TSTA) on the cell surface and the SV40-coded tumour antigen in their nuclei. TSTA is defined by SV40-specific transplantation immunity, whereas T-antigen (T-Ag) can be detected serologically by indirect immunofluorescence. Both antigens, however, are derived from the A gene of SV40. We therefore analysed SV40-transformed cells for the presence of serologically detectable T-Ag-related molecules. Such antigens could not be detected on the surface of living SV40-transformed cells in monolayers. However, after a short formaldehyde fixation it was possible to stain the cell surfaces of SV40-transformed cells with sera from rabbits immunized with purified SDS-denatured T-Ag, but not with sera from hamsters bearing SV40-induced tumours. T-Ag-related antigens could be detected with both types of antisera by applying a more sensitive 125I-protein A assay. The T-Ag specificity of the binding of hamster SV40 tumour sera was demonstrated be a 125I-IgG-blocking assay in which preincubation of formaldehyde-fixed SV40-transformed cells with rabbiet anti-SDS-T-Ag serum inhibited the binding of hamster SV40 tumour serum by about 70%. The localization of T-Ag-related antigens on the outside of plasma membranes of formaldehyde-fixed cells was shown by an anti-SDS-T-Ag serum-specific binding of fluorescein isothiocyanate-labelled Staphylococcus aureus to the cell surface. Out results are consistent with the hypothesis that SV40 T-Ag-related antigens are involved in the formation of TSTA.