[Stereologic analysis of differentiation of immunocompetent cells during reactions of humoral type].

Previous investigations have shown that, during a primary reaction against a single injection of heterologous red blood cells in the Mouse, immunoblasts migrate from the lymph node germinal centers to the medullary cords through the paracortical area. In that study, we combined ultrastructural examination with stereological methods in order to analyze the differentiation of the immunocompetent cells during this migration. The data permit one to characterize two important events in this differentiation. Between the 12th and 24th hour after the antigen injection, when the germinal centers are being dispersed, the cytoplasmic volume of the cells increases 2.5 fold. The estimated number of ribosomes per cell increases from 350,000 to 1 X 10(6) and the volumetric and surface densities of endoplasmic reticulum increase by a factor of 10. Four days later, 120 hours after the antigen administration, the immunoblasts, now located in the medullary cords, show a spectacular increase in the volume and surface density of endoplasmic reticulum, and in the surface density of Golgi membranes. This change results in the transformation of immunoblasts into young plasma cells. Between these two developments, there is a three day period during which the immunoblasts undergo little change.