Evidence is presented for the existence on all B lymphocytes, but not on T lymphocytes, of a membrane-associated receptor for antibody. The receptor was detected by a radioautographic technique in which lymphoid cells were incubated with antibody followed by the corresponding radioiodinated antigen. The ease with which antibody eluted during washing indicated that the bond between antibody and cell was weak. The formation of an antibody-antigen complex on the cell surface, however, stabilized the bond and permitted accurate quantitation of cells with adherent antibody.

The ability of several combinations of antibody and antigen to adhere to the cells demonstrated the nonspecificity of the phenomenon and emphasized the need for care in interpretation of antigen-binding studies particularly when immune cells are being used.

The identity of antibody-binding lymphocytes was established by two different approaches. In the first, mouse lymphocyte populations greatly enriched for either T cells or B cells were examined. Their T cell content was assessed by means of well-established markers such as the θ C3H isoantigen. When this was compared with the number of antibody-binding cells, an inverse relationship was obtained in each instance; thus almost all thoracic duct cells from athymic mice labeled with an immune complex although none were θ positive. The striking reduction in antibody-binding cells observed in bursectomized chickens provided a second and independent line of evidence suggesting that B cells, not T cells, bind antibody.

The ability of B cells from primed animals to bind antibody in vivo made it important to test whether this phenomenon was related to the carriage of immunological memory. No correlation was, however, found between membrane-bound antibody and memory.

It was proposed that the existence of a receptor of this kind may provide a rational explanation for antibody-dependent killing of target cells and may prove of importance in antigen concentration particularly during the secondary response.

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