Anti-θAKR antibody conjugated to fluorescein has been used in direct immunofluorescence tests to identify spleen θ+ (T) sheep erythrocyte rosette-forming cells in AKR mice. Specificity studies involving A and cogenic A/θAKR mice clearly demonstrated that the cell surface fluorescence and cytotoxicity produced by the antiserum is directed solely toward the θAKR alloantigen. Approximately ⅜ of rosette-forming and non-rosette-forming spleen cells were found to be θ+. The tendency for T cells to bind less antigen and the tendency for antigen-binding T cells to bear less θ than other spleen T cells, first suggested by other studies involving rosette-elimination by anti-θC3H plus complement, were confirmed by direct immunofluorescence. All AKR rosettes are specifically inhibitable by anti-immunoglobulin, including T rosettes. Antigen-induced redistribution of T cell receptors, analogous to that previously described for B cell receptors (16), occurs as readily in θ+RFC as in θ- RFC, without altering the symmetrical ring distribution of θAKR antigen.

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