Origins and maturation patterns of azurocytes in the meadow vole (Microtus pennsylvanicus)

Abstract 1. The origins, maturation sequence, and traffic patterns of azurocytes (AZ) were studied in vivo in the meadow vole ( Microtus pennsylvanicus ) with the aid of various biological response modifiers. 2. AZ originated from lymphocyte-like precursors in the bone marrow. These precursors entered into intense mitotic activity in the bone marrow following progestin treatment. 3. While still in the bone marrow, AZ precursors differentiated into granulated cells with some of the histochemical properties of AZ. 4. At this time, maturation could be blocked completely with cyclophosphamide. Hydroxyurea and cyclosporin A inhibited maturation significantly, but did not block it. 5. Estradiol, hydrocortisone, prostaglandin E 2 , and conditioned medium had no effect on the numbers of cells induced. 6. Transitional stages between a granulated bone marrow precursor and an AZ were rarely observed, suggesting rapid synthesis of AZ inclusions upon terminal differentiation. 7. After release from the bone marrow, AZ were common in the blood only. Modest numbers of cells were also found in the red pulp of the spleen, and the thymic cortex. 8. AZ in the thymus were sometimes found in clusters, and were often associated with septa. Very low numbers of mature AZ were detected in the bone marrow. 9. AZ were absent from lymph nodes and Peyers patches, and were never observed in the B-lymphocyte areas of the spleen. 10. Based on experiments with dextran sulphate, AZ and their precursors never entered the recirculating lymphocyte population. AZ in the blood or tissues were never observed in mitosis, and were never observed degranulating. 11. Cyclophosphamide or hydrocortisone had no effect on AZ numbers when administered at the peak of their occurrence in the blood. 12. Although no clear function of the AZ was elucidated, experiments confirmed a high degree of similarity between its properties and those of cytotoxic cells found in other mammals.