Radio-iodinated surface proteins of electrophoretically separated rat lymphocytes

Rat thymocytes and lymph node cells were separated into three T and one B subpopulation by means of free flow electrophoresis. The surface proteins of the separated cells were labeled by lactoperoxidase catalysed radioiodination. Most of the label was demonstrated to be at the cell surface. The labelled cells were either lysed in sodium dodecyl sulphate or treated with Nonidet P-40 to extract cell proteins. The radioiodinated proteins were analysed on sodium dodecyl sulphate polyacrylamide gel electrophoresis followed by autoradiography. In contrast to sodium dodecyl sulphate Nonidet P-40 did not extract cell proteins completely. Furthermore the degree of extraction varied considerably in the different cell populations. 58% of protein bound radioactivity was extracted from thymocytes, 67% from peripheral T cells and 81% from B cells. Gel electrophoresis revealed that four proteins were not extracted at all, whereas five components were better soluble in Nonidet P-40 than all other proteins. One protein was extracted from B cells only although it was present in all cells. Although the surface protein patterns of the four lymphocyte subpopulations were rather similar, distinctive differences could be found. B cells had six labelled proteins which seemed to be absent in the other cells, In the T cell group, three protein bands were identified, each with specificity for peripheral T cells, thymocytes and all T cells respectively. Four other proteins were found which showed quantitative differences between the four cell groups.