Studies on precursors of hemolytic plaque-forming cells: Effect of the specific removal of natural PFC by erythrocyte-conjugated Sepharose beads on the responsiveness of depleted spleen cells

Influenza virus particles, inactivated with formalin, have been covalently bound to cyanogen bromide-activated Sepharose beads (Se-vi beads). Preservation of the hemagglutination properties of the viral particles enabled a strong binding of pigeon or human group O erythrocytes (PRBC or HoRBC) to these Se-vi beads. The conditions for preparation of PRBC- or HoRBC-Se-vi columns are described. Spleen cell suspensions from mice immunized with the above erythrocytes were considerably depleted of cells forming hemolytic plaques (PFC) against the corresponding erythrocytes after passage through these columns. In the case of cells from nonimmunized mice, the depletion is still greater and reaches up to 95–100%. However, the number of PFC reactive to unrelated erythrocytes is not affected in the filtered population. Specifically attached cells recovered from the Se-vi-RBC columns passed with normal spleen cells are considerably enriched in the number of PFC against homologous erythrocytes. Syngeneic irradiated hosts transferred with filtered cells are able to give a normal primary PFC response against heterologous, but not against homologous RBC up to the 12th day after immunization. These results are discussed in relation to the problem of precommitment of specific PFC precursor cells.