The transformation of small peripheral blood lymphocytes into large pyrinophilic lymphoblasts is a biologic event that has been extensively studied over the last two decades (11). The initial discoveries that this transformation could be accomplished both non-specifically by plant lectins (mitogens) and specifically by defined antigens has greatly enhanced our understanding of the immune system (3,13). Initial studies of lymphocyte transformation or blastogenesis were performed by examining stained specimens and manually counting transformed and nontransformed cells. This technique is highly accurate and definitive, but tedious. In addition, per cent calculations of transformed cells were frequently inaccurate due to the failure to recognize increases in small lymphocytes during the period of culture. Figures 17.1 and 17.2 illustrate the changes that occur both in lymphoblast number and small lymphocyte number following either mitogen or antigen stimulation. It can be seen that following mitogen stimulation, lymphoblast numbers rise sharply.

Eight normal donors were serially tested over a period of 1 to 7 months for their in vitro lymphocyte responsiveness (IVLR) to 50 microgram of concanavalin A (Con A) per ml. 3H-Thymidine incorporation was monitored by routine scintillation counting and compared to actual numbers of proliferating cells (lymphoblasts) as measured by laser (flow) cytometry. Determination of total cell numbers or lymphoblast numbers was found to be superior (P less than 0.0001 and P less than 0.001, respectively) to 3H-thymidine incorporation as a measure of serial stability.