Myelopoiesis in lymph nodes of mice. Enhancement effect by the injection of trypan blue or India ink after birth.

Myelopoiesis in lymph nodes was studied in newborn mice under normal conditions and after treatment with trypan blue and carbon particles. In the mouse lymph node, myelopoiesis normally takes place between the fourth and twelfth day after birth, then decreases while an intense proliferation of the lymphocytic population simultaneously takes place. Myelopoiesis manifests itself as clusters of cells, mainly of the neutrophilic line, located around post-capillary venules (PCV's) in the medulla. The injection of trypan blue or carbon particles (India ink) causes an enhancement of myelopoiesis and a delay in the development of the lymphocytic population. Myelopoiesis includes not only granulopoiesis but also the formation of erythroid clusters and occasional megakaryocytes. Three possibilities should be considered to explain the enhancement of myelopoiesis: 1) blockade of the reticuloendothelial system caused by overloading with particulate matter; 2) induction of humoral myelopoiesis-stimulating factors; and 3) stimulation of pluripotent stem cells through dye injection.