Disclosed are methods relating to cell membrane fragments associated with
microbeads, so that the characteristics of the cells the fragments
originated from can be determined. The fragments can be oriented with
what was the outer surface of the cell membrane facing outwardly, so that
the antigens associated with the membrane can be contacted with ligands
(including antibodies) to antigens in the membranes which would be
accessible to antibodies in vivo. The system is useful, inter alia, for
detection of panel reactive antibodies in donor serum, as well as
detection of other cell membrane antigens; or quantitation of particular
cell membrane antigens.