IMAGE-ANALYSIS OF DENDRITIC CELLS IN THE HUMAN FETAL THYMUS

The distribution and evolution of thymic dendritic cells (DC) were stu died during human ontogeny. Immunochemical techniques were used to det ect S100 protein-positive cells on fetal thymus sections, at different post-fecundation (PF) ages; an image analysis of these positive cells was then carried out. Variations in the percentage of these cells in the medulla were determined according to age: the higher percentages w ere seen at 12 and 16 weeks PF. Dendritic cells were present at an ear ly stage in the thymic rudiment (7 weeks PF), a finding consistent wit h an origin of these cells in the fetal liver, and with the possible e xistence of local attraction and/or maturation factors. The expression of the CD54 adhesion molecule revealed the existence of particular in teractions between DC and lymphocytes in the medullary area, and at th e cortico-medullar junction. Diffuse CD11a (LFA-1) expression on lymph ocytes was consistent throughout gestation. The monocyte/macrophage ma rkers (CD11b, CD14) and the reaction of non-specific esterases showed that the distribution pattern of these cells differed from the DC patt ern. These ontogenic data are related to the significant role played b y DC throughout the different stages of thymopoiesis.