Efficient radioiodination and immunopurification of surface proteins from small numbers of cells

This report describes a method for the cell surface radioiodination and immunoprecipitation of the T cell receptor from as few as 7.5 x 10(4) lymphoid cells. The membranes of cells were labelled using the lactoperoxidase/H2O2 method. In order to minimize the loss of labelled cells after iodination, T cell receptor-negative 'filler' cells were added to the washes and the washing volume was kept small. Before immunoprecipitation, the solid-phase Staphylococcus aureus was precoated with the specific monoclonal antibody to ensure optimal recovery of antibody-antigen complexes. These simple modifications greatly increased the efficiency of the iodination and immunoprecipitation procedures, thus enabling direct analysis of membrane proteins from small numbers of cells.