The Proliferative Capacity of Antigen-Sensitive Precursors of Hemolytic Plaque-Forming Cells

Abstract

The antigen-sensitive precursors of hemolytic plaque-forming cells (7, 8) can be transplanted into heavily-irradiated mice. In the presence of antigen, these cells proliferate and differentiate, giving rise to progeny which form clusters detectable by their capacity to produce foci of hemolysis in a layer of agar containing sheep erythrocytes. The enumeration of such foci provides an assay techniques for antigen-sensitive cells (9). When the same spleen cell suspensions were assayed for these cells both by this technique and by the method of limiting dilution, both techniques yielded similar values. This similarity indicates that the hemolytic focus assay does indeed detect antigen-sensitive cells. By combining assays for antigen-sensitive cells and for their hemolysinproducing progeny, we have obtained an estimate of 4 to 7 for the number of divisions which result from the stimulation of antigen-sensitive cells by sheep erythrocytes. By a technique of serial transplantation, the fraction, f, of the total number of injected antigen-sensitive cells which are detectable in the spleens of heavily-irradiated mice following the intravenous injection of spleen cells was determined to be 0.15. Using this value, f, along with the number of antigen-sensitive cells detected in a given number of spleen cells and the number of cells in normal mouse spleens, one may calculate that there are approximately 10³ antigen-sensitive cells in intact spleens. This estimate agrees with a previous value obtained using a radiobiologic technique (4).