Glomerular Size in Transplanted Kidneys: Does Size Matter?

Abstract

The glomerulus is a remarkable structure. The glomerular tuft is a meshwork of specialized capillary vessels that operates at high hydrostatic pressures (approximating 55 mm Hg) supported by specialized type IV collagen with high tensile strength, to produce glomerular ultrafiltration into Bowman's space as the first stage of urine formation. Intraglomerular pressures are controlled by differential afferent and efferent resistance vessels, which are controlled by tubular-glomerular feedback, the reninangiotensin-aldosterone system and prostaglandins. The glomerulus is composed of 600-700 cells (mostly mesangial and endothelial cells, fewer visceral epithelial cells). Their health within a transplanted kidney can affect function, proteinuria, and outcomes.Measuring glomeruli would seem like a good idea, and multiple studies in transplanted and native kidneys have found relationships with glomerular size with outcomes, although not always in a common direction. 1,2 In current study published in this edition of Transplantation, 3 Grande et al obtained 1027 indication biopsy samples for transplant dysfunction and measured glomerular planar surface area and diameter by image analysis on all glomeruli containing a vascular pole (excluding sclerosed glomeruli) from the 2 cohorts of the Deterioration of Kidney Allograft Function study. BKV infection and recurrent glomerulonephritis were excluded.The study reported glomerular size increased with time (r = 0.317) and was greater in the later cross-sectional cohort (mean 7.7 ± 5.6 y posttransplant) compared with early prospective cohort which used the first biopsy-for-cause samples (at 1.7±1.4 y), congruent with the findings from studies. An adaptive response to hyperfiltration (a weak association with recipient BMI was noted), or more likely, a greater prevalence of chronic-active antibody-mediated rejection