Ultrastructural immunogold labeling patterns--image processing, mapping and quantitative microanalysis of antigenic sites in renal biopsies and neoplasms

Tubular Injury and Dendritic Cell Activation Are Integral Components of Light Chain-Associated Acute Tubulointerstitial Nephritis

CONTEXT.—

Light chain-associated acute tubulointerstitial nephritis (LC-ATIN) is a variant of light chain proximal tubulopathy (LCPT). It is characterized by interstitial inflammation with tubulitis and deposition of monoclonal light chains in the tubulointerstitium. LC-ATIN is a rather poorly recognized pattern of LCPT and not much is known about this entity.

OBJECTIVE.—

To determine the clinicopathologic features of patients with LC-ATIN and investigate the proximal tubular injury and mechanism of interstitial inflammation in LC-ATIN.

DESIGN.—

A total of 38 cases of LC-ATIN were identified from the archives of 5043 renal biopsy specimens. In all cases, routine light microscopic examination, immunofluorescence, and electron microscopic examination were performed. In selected cases, immunofluorescent staining of dendritic cells and immunohistochemical staining for 4 tubular injury markers-KIM-1, p53, bcl-2, and Ki-67-were performed.

RESULTS.—

A characteristic finding in LC-ATIN cases was immunofluorescence staining of monoclonal light chains along tubular basement membranes in linear fashion and inside proximal tubular cells with a granular pattern. No monoclonal light chains were present in glomerular or vascular compartments confirmed with immunofluorescence, electron microscopy, and ultrastructural gold labeling. Ten of 15 LC-ATIN cases (67%) were concurrently positive for the 4 tubular injury markers. Dendritic cells were identified within the tubulointerstitium in the renal biopsy specimens, interacting with surrounding tubules with light-chain deposits and inflammatory cells.

CONCLUSIONS.—

Significant proximal tubular injury occurs associated with LC-ATIN, and the monoclonal light chains accumulated in proximal tubular cells contribute to the injury. Dendritic cells are involved in the pathogenesis of interstitial inflammation in LC-ATIN.

Proximal tubulopathies associated with monoclonal light chains: the spectrum of clinicopathologic manifestations and molecular pathogenesis

CONTEXT

Lesions associated with monoclonal light and heavy chains display a variety of glomerular, tubular interstitial, and vascular manifestations. While some of the entities are well recognized, including light and heavy chain deposition diseases, AL (light chain) and AH (heavy chain) amyloidosis, and light chain ("myeloma") cast nephropathy, other lesions centered on proximal tubules are much less accurately identified, properly diagnosed, and adequately understood in terms of pathogenesis and molecular mechanisms involved. These proximal tubule-centered lesions are typically associated with monoclonal light chains and have not been reported in patients with circulating monoclonal heavy chains.

OBJECTIVE

To determine the incidence of proximal tubulopathies in a series of patients with monoclonal light chain-related renal lesions and characterize them with an emphasis on clinical correlations and elucidation of molecular mechanisms involved in their pathogenesis.

DESIGN

A study of 5410 renal biopsies with careful evaluation of light microscopic, immunofluorescence, and electron microscopic findings was conducted to identify these monoclonal light/heavy chain-related lesions. In selected cases, ultrastructural immunolabeling was performed to better illustrate and understand molecular mechanisms involved or to resolve specific diagnostic difficulties.

RESULTS

In all, 2.5% of the biopsies were diagnosed as demonstrating renal pathology associated with monoclonal light or heavy chains. Of these, approximately 46% were classified as proximal tubule-centered lesions, also referred to as monoclonal light chain-associated proximal tubulopathies. These proximal tubulopathies were divided into 4 groups defined by characteristic immunomorphologic manifestations associated with specific clinical settings.

CONCLUSIONS

These are important lesions whose recognition in the different clinical settings is extremely important for patients' clinical management, therapeutic purposes, and prognosis. These entities have been segregated into 4 distinct variants, conceptualized morphologically and clinically. Specific mechanisms involved in their pathogenesis are proposed.

Immunoelectron microscopy in the age of molecular pathology

The introduction of molecular biology-based diagnostic procedures in pathology has created substantial expectations in regard to screening, characterization, monitoring, and detection of predisposition to a variety of diseases, most notably malignant neoplasms. It should be emphasized, however, that molecular studies are only one component of the diagnostic process and that more traditional methods are still required in the evaluation of tumors and management of patients. The data obtained from the molecular biology-based studies must be always interpreted in conjunction with the clinical history, immunomorphologic findings, and other pertinent ancillary data. Routine evaluation of tissues using traditional light microscopy remains the backbone of pathologic evaluation. The additive role of molecular diagnostics often depends on how accurate the initial evaluation has been. Ancillary techniques such as immunohistochemistry and electron microscopy remain essential in properly characterizing diseased tissues and in speciation of tumors. Ultrastructural immunolabeling capitalizes on combining these two techniques and providing exquisite immunomorphologic evaluation. The extra time and effort required are more than compensated by the degree of sophistication that can be achieved when this diagnostic technique is utilized and the added expense is rather reasonable. The value of molecular biology-based diagnostics is potentially questionable if the tissue samples are not initially accurately characterized. The question that molecular diagnostics may be trying to answer may be the wrong one or the answer obtained may be interpreted incorrectly if the context of the clinicopathologic situation has not been clearly defined using traditional diagnostic techniques.

Ultrastructural immunolabeling in the evaluation, diagnosis, and characterization of neuroendocrine neoplasms

Neuroendocrine neoplasia represents a heterogenous entity with variable morphologic light microscopic expressions. In many cases a definite diagnosis is easily made by light microscopic examination, but in some cases this does not suffice. In the latter instances, immunocytochemistry, ultrastructural examination, or both are required to diagnose a neuroendocrine neoplasm. However, basing a diagnosis of neuroendocrine neoplasia exclusively on the results obtained from immunocytochemical or ultrastructural evaluation of these tumors may not be entirely accurate in some instances. Ultrastructural immunolabeling plays a key role in accurately defining localization of immunoreactive substances in well-characterized neuroendocrine neoplasms, can assess colocalization of antigenic epitopes, helps define specificity and significance of immunocytochemistry results obtained at the light microscopic level, and is more sensitive than light microscopic immunocyto-chemistry. Some evolving diagnostic entities can be further characterized by utilization of ultrastructural labeling techniques. Controversies concerning the neuroendocrine nature of electron-dense structures identifiable at the ultrastructural level can be readily and accurately resolved. By providing a way to evaluate combined immunomorphologic parameters, ultrastructural immunogold labeling can settle important questions pertaining to neuroendocrine neoplasia. The present article illustrates a series of cases where the above-mentioned applications were tested.

Microanalytical techniques and image analysis in the evaluation of immunogold-labeled specimens at the ultrastructural level

Energy-dispersive X-ray microanalysis (EDX) interfaced to a scanning/transmission electron microscope allows direct visualization and photographing of structures analyzed under the electron beam. EDX can perform a point-by-point analysis as it searches for the ion whose X-ray window the computer has been instructed to localize. This technique has been utilized to define ultrastructural immunogold labeling patterns. Once a specimen is immunolabeled with gold, microanalytical techniques can identify the quantity and distribution of detected and labeled antigenic epitopes. Microanalytical techniques add a new objective dimension to ultrastructural gold labeling procedures. Quantitative microanalysis of the gold-labeled antigenic sites provides a way of assessing the specificity of the reactions and permits comparison of the degree of expression of antigenic determinants in different specimens. Image processing allows visual representation of the immunolabeling results. Furthermore, statistical analysis of a large number of parameters is also possible with the digitized images collected. Ultrastructural microanalytical techniques represent a new, unexplored application that may play an important role in the future of ultrastructural pathology and immunologic evaluation of diseased tissues.

Ultrastructural immunolabeling: a general overview of techniques and applications

Ultrastructural immunolabeling techniques combine the advantages of routine electron microscopy and detection of antigenic epitopes, the latter of which is customarily done by immunocytochemistry at the light microscopic level. In surgical pathology, immunocytochemistry has become routine to approach the differential diagnosis of difficult cases. Immunoelectron microscopy has been used primarily for research purposes or for addressing specific questions in diagnostic pathology. Ultrastructural immunolabeling is extremely useful in those instances in which the ultrastructural and immunocytochemical findings are not pathognomonic and are subject to interpretation. Preembedding and postembedding labeling techniques have been described in the literature. Preembedding techniques are not as applicable to diagnostic work, however. Their use remains rather limited to applications in which the antigen to be labeled cannot maintain its viability when exposed to fixatives. Even in such cases a new methodology--the LifeCell process--has emerged; this technique cryofixes tissues, thereby maintaining antigenic integrity. After cryofixation, a postembedding labeling technique can be utilized. Immunogold and peroxidase methods are used for labeling. Immunogold methods elegantly mark reaction sites with preservation of underlying morphology. Postembedding immunogold methods are used by most individuals working in the field. Ultrastructural labeling techniques are rapidly moving from classification as exclusively research tools to the diagnostic arena.