Isolation of Plasma Membrane Antigens from Epstein-Barr Virus-Infected Lymphoid Cells

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Abstract
The plasma membrane fraction of Epstein-Barr virus (EBV)-infected lymphoid cells was isolated on sucrose density gradients in an attempt to also isolate EBV-coded membrane antigen (MA). The surface HL-A and xenoantigens of these cells were readily isolated in this way. The location of antigens on the gradients was monitored by bound radioiodine-labeled proteins from MA-reactive sera and normal sera introduced by incubation of intact cells with labeled proteins before fractionation (paired-label technique). Though the cells used were 40% positive for MA by membrane immunofluorescence before fractionation, No detectable MA remained associated with the plasma membrane after fractionation. However, a peak of antibody-bound material appeared in the denser region of the gradients which contained EBV by electron microscopy. No detectable soluble MA-antibody complexes were released during the isolation procedure. In contrast to the stronger bonds which hold HL-A and xenoantigens to the plasma membrane, the MA-membrane bond appears to be weak enough to be broken during hypotonic treatment and mechanical rupture of the cells. We conclude that the majority of cells in an EBV carrier culture that are positive for MA by immunofluorescence may be carrying EBV and MA-positive membranous debris adsorbed to their surfaces derived from the perinuclear and endoplasmic membranes of degenerating infected cells.

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