Enrichment of memory cells carrying receptors for a protein antigen (hsa).

Sheep red cells (RC) were coupled with HSA by means of an HSA—anti-SRBC IgG conjugate. The coupled RC were used to prepare rosettes with spleen cells of mice immunized to HSA in Freund's complete adjuvant. The rosettes were fractionated on discontinuous Ficoll gradients and the rosette-rich and rosette-poor fractions were tested for ability to transfer adoptively secondary responsiveness to HSA. Efficiency of transfer was measured in terms of haemagglutination titres. Memory of HSA was shown to be associated with rosette-forming cells, i.e. with cells carrying receptors for HSA. Several parameters of the adoptive transfer system employed were studied. The HSA-coupled RC proved to be very efficient in stimulating secondary responses to HSA. High titres of haemagglutinating antibodies (up to 1/80,000) were obtained with 10 × 106 spleen cells transferred and 2 × 106 spleen cells consistently gave titres of the order of 1/10,000.