Isolation of antigen-binding cells from unprimed mice. II. Evidence for monospecificity of antigen-binding cells.

Spleen cells from unimmunized mice were exposed to two contrastingly fluorescent antigens simultaneously. Antigen-binding cells of either specificity were isolated using a fluorescence-activated cell sorter (FACS). Purified cells binding one or the other of the antigens were then examined by fluorescence microscopy for the presence of bound antigen of the alternate specificity. No double binding cells were seen. If cells bear receptors of two or more specificities and these receptors are randomly distributed among antigen-binding cells, then of the 13 000 binding cells examined 82 were expected to bind both antigens. These results strongly suggest that antigen-binding cells bear receptors of only one specificity. In addition, by inference from the functional correlation between antigen-binding cells and precursor cells, the data support the contention that precursors of antibody-forming cells are monospecific.