Ultrastructural labeling can play a key role in the evaluation of morphologic expressions of monoclonal light chain-related renal diseases in cases where light microscopy, electron microscopy, and immunofluorescence data, even when combined, are not definitive in conveying a diagnosis and, in other cases, in clarifying the findings by providing immunomorphologic correlation. The important role of ultrastructural labeling is highlighted by the fact that in some of these cases bone marrow aspirates and biopsy specimens obtained at the time of the evaluation of the renal specimens are often unable to establish unequivocally a diagnosis of plasma cell dyscrasia. This is in part because renal manifestations commonly precede overt diagnostic bone marrow alterations. Overt bone marrow findings and clinical manifestations may be preceded for as long as 16 years by the renal manifestations. Determination or confirmation of monoclonality and detection of early deposition of monotypical light chains before the finding of ultrastructural morphologic correlates (ie, subendothelial, punctate, granular, electron-dense material) represent unique attributes of this technique. The increased sensitivity of ultrastructural immunolabeling compared with other available diagnostic techniques and its exquisite immunomorphologic correlative capabilities result in a comprehensive evaluation. Sixteen monoclonal light chain-related renal disease cases with early, unusual, or equivocal immunomorphologic manifestations that may have not been characterized properly if ultrastructural labeling had not been performed are presented. The crucial role played by ultrastructural labeling in evaluating these cases and establishing an accurate diagnosis is illustrated and emphasized.

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β2-microglobulin is a single-chain, low molecular weight (MW=11.8 kDA) polypeptide [1,2] and has similar structure to the CH 3 domain of the immunoglobulin molecule [3]. β2-microglobulin forms the invariant light chain portion of major histocompatibility complex (MHC) class I molecules [4][5][6], which can be found on the membrane of all nucleated cells [7]. Thus, cellular membrane turnover is the main source of serum β2-microglobulin [3]. Because of its small size, β2-microglo- Objective: After filtration through the glomeruli of the kidney, β2-microglobulin is reabsorbed by the renal proximal tubules. Increase in urinary β2-microglobulin indicates tubular dysfunction, and measurement of β2-microglobulin in urine sediment is useful to determine the source of kidney injury. CD133 has recently been characterized as a progenitor cell marker in the kidney, detecting injured epithelial cells in the proximal tubules. This study was designed to evaluate the correlation of increase in urinary β2-microglobulin and CD133 staining in patients with tubular injury. Urinary β2-Microglobulin is a Sensitive Indicator for Renal Tubular InjuryAbstract

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