Histological study of the renal lymphatic tissues in mice *
The occurrence of lymphatic tissues in the kidney was examined by light microscopy in 52 ICR-mice of both sexes aged 30, 90, 180 days and 1 year old. The excised kidneys were fixed in Bouin's fluid and embedded in paraffin for serial sections. Some kidneys were also fixed in Karnowsky's fluid for 1μm plastic sections. Renal lymphatic tissues were three-dimensionally reconstructed from serial paraffin sections by a computed image analyzer. The mouse kidney was unilobar with a simple structure. The kidney parenchyma was closely packed with nephrons, and small amount of connective tissue could be recognized beneath the renal capsules, around large vessels running in the kidney and at the renal pelvis. Under 90 days of age, the connective tissues contained a few free cells such as small lymphocytes and plasma cells, but no lymphocytic cell aggregations were found. After 180 days, however, both plasma cells and small lymphocytes increased in number and aggregated nodularily, forming lymphatic tissues in renal connective tissues. Two kinds of lymphatic tissues could be observed in the kidney of aged mice : (1) lymphatic tissues at the cortico-medullary junctions and (2) those at the renal pelvis. Lymphatic tissues in the renal pelvis formed in the lamina propria mucosae of the pelvis between the epithelium and the pelvic veins. The lymphatic tissues at the cortico-medullary junctions were nodular masses in connective tissues between the cortex and medulla. These lymphatic tissues, measuring 0.1～0.2 mm in diameter, lay between arcuate arteries and veins or surrounded the bifurcating portions of the arcuate arteries and contained a large number of mature plasma cells. Occasional cells had a few very large rounded cytoplasmic inclusions called Russell bodies. They were primary lymphatic follicles without germinal centers, but both large lymphocytes and mitotic figures were sometimes noted. In the present study, the development of primary lymphatic tissues containing a large number of plasma cells was observed in the kidneys of aged mice. These plasma cells were also scattered singly or in small groups in the narrow connective tissue beneath the renal capsule and among urinary tubules. The functional significance of the renal plasma cells was discussed in relation to urinary immunoglobulin. (Accepted on March 29, 1997) Kawasaki Igakkaishi 23(1) : 7―17, 1997
