The monocyte/macrophage population of the normal human kidney

There is continuing controversy over the role of mononuclear phagocytes in glomerulonephritis. It is, therefore, important to know their distribution in normal subjects. Normal kidneys (34) were assessed using three cytoplasmic markers for macrophages employing a trypsin–immunoperoxidase (PAP) technique with antibodies to α‐1‐antitrypsin, muramidase (lysozyme) and a further oligoclonal antibody, serum 22, developed against highly purified preparations of blood monocytes. Serum 22 detected twice as many monocytes/macrophages as anti‐muramidase and four times as many as anti‐α‐1‐antitrypsin. Most cells that showed positive staining lay in glomerular and intertubular capillaries and were considered to be blood monocytes. There was wide variation in monocyte numbers throughout different glomeruli and up to 14 monocytes could be present in a glomerulus. Not more than 1 per cent lay within the mesangium. Macrophages were virtually never seen in the interstitium, except in areas of scarring. No macrophages were present in the tubules. Monocytes and macrophages are demonstrated in greater numbers within the kidney by antisera to muramidase than to α‐1‐antitrypsin.