© 2003 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003

15.4.3.2.5 Phagocytosis in Kidney Vasculature

The normal human kidney contains blood monocytes mostly in the glomerular and intertubular capillaries, with wide variation in the numbers present in different glomeruli but up to 14 monocytes present in a single glomerulus [2970]. Not more than 1% of monocytes reside within the mesangium [2970]. Macrophages normally are not found in the tubules and are virtually never seen in the interstitium, except in areas of scarring [2970]; possibly in areas of oxalate crystal deposition in nephrolithiasis [2971]; in fetal kidneys [2972, 2973]; and in diseased kidneys [2974, 2975] when macrophages can be found in the Bowman’s space and the mesangial area of the glomeruli [2974], and leukocyte infiltration is also seen [2976]. Macrophages found in the kidney generally behave much like macrophages elsewhere in the body.

The mesangium is the core of the renal glomerulus and the preferred destination of the induced migration of monocytes during inflammation [2977]. Mesangium consists of the matrix (mucopolysaccharides and glycoproteins) and two cell types – at least 85% contractile mesangial cells, which resemble smooth muscle cells, and up to 15% resident mesangial phagocytes, derived from bone marrow [2978] and belonging to the family of mononuclear leukocytes [2977]. Mesangial phagocytes ingest proteins and particulate material [2979, 2980] including zymosan particles [2981], apoptotic cells [2982], and of course the familiar colloidal carbon [2983-2989], internally releasing reactive oxygen species like other phagocytes [2995]. In one interesting experiment, monocytes that had previously ingested inert latex microspheres migrated into rat kidneys whose glomeruli had been denuded of mesangial cells and occupied the vacant cell sites (after 24 hours), transforming first into macrophage-like cells (after 4-6 days) and later into cells indistinguishable from normal mesangial cells (after 2-4 weeks) [2996].

However, there have been relatively few investigations of the details of particle ingestion by kidney-resident or kidney-infiltrating phagocytes [2989-2994]. For example, BSA-coated colloidal gold particles injected IV into ducks were mostly trapped in the mesangial channel system, phagocytized by mesangial cells, exocytosed back into the mesangial channels, transported extracellularly towards the vascular hilus, rephagocytized by macula densa cells, then expelled into the tubular lumen [2992]. Another study found that during glomerulonephritis, macrophages accumulate at sites of inflammation and subsequently migrate to the draining kidney lymph nodes [2997]. This suggests one possible fate of renal macrophage infiltrates after their ingestion of large quantities of completely passive medical nanorobots.

Last updated on 30 April 2004