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Antigen Binding Cells in Tolerance and Immunity

It has been stated (e.g. Mitchison 1969) that a minimal theory for antibody production requires the following three postulates: (1) One cell makes one immunoglobulin. (2) The gene which specifies this immunoglobulin is present in the cell prior to antigenic stimulation. (3) Immunoglobulin corresponding to the synthetic capabilities of a cell is present in or on the cell prior to stimulation, where it signals to the cell, after suitable binding of the appropriate antigen has occurred, that the time has come to transform, multiply and secrete antibody. There is now a substantial amount of evidence which suggests that these postulates are essentially correct and that future work lies in the further study of the final two of the three postulates. One of the techniques which has contributed to the evidence supporting this theory is the Antigen Binding Reaction which allows the binding of antigen to a lymphocyte (or other cell) to be visualized by means of radioautographic techniques, using either the light microscope or the electron microscope. The advantage of this technique is that it allows individual cells in populations of cells to be examined and, if sufficient patience is exercised, for this to be done in at least a semi-quantitative manner. The purpose of this article is to review some of the parameters of this reaction and to compare the results obtained by several investigators who have studied the binding of antigen to cells from normal, immunized and tolerant animals. Some of the questions which can be asked as a result of these findings can then be discussed. It is hoped that the reader will thus be made aware of both the potential and the limitations of the technique. When radiolabelled antigens are injected into unimmunized animals and the fate of radiolabel followed in lymphoid tissues, one of two distinctly dif-