Ontogeny of human lysozyme. Distribution in fetal tissues

Using the immunoperoxidase method, major changes in the distribution of lysozyme (LZM) were found to occur during fetal development. At 10 weeks of gestation LZM was detected for the first time in the proximal tubules of the kidney. This generally coincides with the reported appearance of LZM in fetal blood and amniotic fluid. The enzyme was observed in lung macrophages and in mononuclear cells of the lamina propria of the small intestine in fetuses 12 and 16 weeks old, respectively. At about 18--20 weeks, LZM-positive mononuclear cells were detected in other tissues tested, such as liver, spleen and thymus. Paneth cells were found to be specifically stained at about 20 weeks of gestation. The timing of the appearance of LZM in the various tissues is discussed in relation to the functional maturation of each organ and the ontogeny of this enzyme in other species.