Localization of Fc receptors in human and rat malignant tissues

Three human malignant tumors and a rat carcinoma (Walker 256), which all showed strong Fc receptor activity in tests with sheep erythrocytes (E) sensitized with rabbit IgG antibodies (A), were used to study the distribution of the receptor in subcellular fractions isolated by differential centrifugation. Smears of the three crude sediments obtained (nuclei, mitochondria rich and membrane rich) all possessed receptor activity. EA incubated in the suspension of cell fractions did not attach to Fc receptor positive tissue sections or to cells in suspension. Cells from which the surface receptors had been eluted still showed activity in sections of cell pellets. Apparently the Fc activity is connected with both external and internal membranes.