| Abstract|| |
Tubulo-reticular inclusions (TRIs) are organized subcellular structures that may be found in endothelial cells of patients with systemic lupus erythematosus (SLE). This study was conducted to determine the presence or absence of TRIs and their correlation with the activity index (AI) and lupus nephritis (LN) class. A retrospective analysis of 57 cases of LN over a three-year period (2008-2011) was performed from medical records of the King Khalid University Hospital (KKUH), Riyadh. After reviewing and sorting them by class as per the International Society of Nephrology (ISN/RPS) 2004 classification of LN, the cases were divided according to the presence or absence of TRIs. The relationships between the presence or absence of TRIs and the AI were determined. Of the 57 kidney biopsies reviewed, 49 were proliferative cases (Class III and IV), of which 12 (24.5%) had TRIs. The mean AI was 6.01 ± 3.8 and the mean chronic index was 3.0 ± 1.5. Four (11.4%) class IV cases had a high AI, while no Class III cases with TRIs showed increased activity. The presence of TRIs was significantly associated with the AI (r = 9.40, P = 0.002), but not with LN class (r = 0.099, P = 0.753). Examining for TRIs in LN is still favorable and helpful in cases where the diagnosis of SLE is pending or not yet established, although the presence of TRIs is not a specific finding.
|How to cite this article:|
Kfoury H. Tubulo-reticular inclusions in lupus nephritis: Are they relevant?. Saudi J Kidney Dis Transpl 2014;25:539-43
| Introduction|| |
Tubulo-reticular inclusions (TRIs) are organized subcellular structures measuring 20-30 nm in diameter forming reticulum structures, which may be found in the endothelial cells of patients with systemic lupus erythematosus (SLE). , When found in other settings, TRIs evoke a suspicion of underlying diseases, such as viral infection, autoimmune diseases and collagen vascular disorders. , Although rare (occurring in fewer than 5% of patients), TRIs are observed in patients with most forms of renal disease. TRIs are frequent in patients with HIV-associated nephropathy (HIVAN) or SLE or those undergoing alfa-interferon therapy. , Endothelial TRIs are identified in about 80-90% of HIVAN.  In acquired immunodeficiency syndrome, TRIs have been described in various tissues throughout the body including the lung, kidney, liver, muscle and skin. , TRIs are an expression of a systemic stimulus. They can be suggestive of SLE or HIV infection, but not a marker of a particular type of renal disease. ,
In lupus nephritis (LN), glomerular changes are highly variable including the presence of immune deposits, increased cellularity, endo-capillary proliferation, [Figure 1] thickening of capillary walls, glomerular tuft necrosis, crescents, karyorrhexis, hyaline thrombi and glomerular sclerosis.  The frequency of nephritis, particularly the International Society of Nephrology (ISN/RPS) Class III and IV, is high in SLE patients who may not demonstrate clinical symptoms despite high titers of anti-dsDNA antibodies and low concentration of C3. The presence of TRIs in LN is not a specific finding; however, some reports have shown that TRIs are more significantly associated with early signs of lupus than a "full-house" immunofluorescence glomerulopathy, especially in pediatric patients.  Disease activity is usually defined by the activity index (AI) in the kidney biopsy, especially in Class III/IV glomerulonephritis. ,,,
|Figure 1: A glomerulus showing segmental endocapillary proliferation (arrow) (PAS stain ×40).|
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The aim of this study was to investigate the presence of these TRIs among patients with proliferative LN to investigate whether their presence is correlated with the AI and histological classification of the disease.
| Methods|| |
Renal biopsy findings in LN patients treated at the King Khalid University Hospital (KKUH) in Riyadh, Saudi Arabia, between January 2008 and December 2011 were analyzed. The inclusion criterion for this study was a diagnosis of LN.
The reviewed renal biopsies were re-examined under a transmission electron microscope (TEM) for the presence and distribution of the TRIs as defined earlier [Figure 2] and [Figure 3]. All cases were thoroughly screened at high magnification starting from 10,000×. The presence of TRIs in the endothelial cell cytoplasm of the glomerular capillary walls was recorded in the studied LN cases and correlated with the AI, the chronicity index and the class of LN [Table 1]. The determination of the activity and chronicity indices was performed according to the scoring system of Pollak et al, as modified by Austin et al. ,
|Figure 2: Electron photomicrograph of a glomerulus showing prominent subendothelial dense deposits (arrowhead) and TRI (arrows) (Uranyl acetate, lead citrate, ×15,000).|
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|Figure 3: Electron photomicrograph of a glomerulus showing the TRI (arrows) (Uranyl acetate, lead citrate, ×25,000).|
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The histopathological profiles of the biopsies were reviewed with a focus on the potential relationships with the AI and the LN class.
| Statistical Analysis|| |
Data were analyzed using predictive analysis software (PASW version 18, IBM, Chicago, IL, USA). Data are presented as the mean ± standard deviations and percentages. Correlations were performed using the chi-squared test and independent t-test. Statistical significance was considered at P-value <0.05.
| Results|| |
A total of 57 kidney biopsies were reviewed. Of these, 14 (20.6%) were Class III LN and 35 (51.5%) were Class IV LN. The remaining seven (10.3%) of Class II, V and VI LN cases were not included in the analysis because the activity and chronicity scores were not applicable.
Of the 49 proliferative cases of LN (Class III and IV), 12 (24.5%) had TRIs. The mean AI was 6.01 ± 3.8 (median of 6.0) and the mean chronic index (CI) was 3.0 ± 1.5 (median of 3.0). Four (11.4%) Class IV cases had an increased AI (>11), while none from Class III was increased.
The AI was significantly higher in Class IV (7.13 ± 3.9) compared with Class III (3.38 ± 2.1), P = 0.002. There were no significant differences in the mean CI between Class III (3.36 ± 1.6) and Class IV (2.87 ± 1.5) cases, P = 0.329.
Three of the 14 (21.4%) Class III cases and nine of the 35 (25.7%) Class IV cases had TRIs. The presence of TRIs was not significantly correlated to the classification (r = 0.099, P = 0.753). In contrast, five of the 12 cases (41.7%) with TRIs had an increased AI (>11). The seven remaining cases with TRIs had an AI <11. The AI was significantly associated with the presence of TRIs (r = 9.40, P = 0.002).
There were no correlations between the presence of TRIs and the LN class (r = 0.028, P = 0.841) or CI (r = -0.136, P = 0.324). The LN class positively correlated to the AI (r = 0.268, P = 0.048), but not to the CI (r = -0.185, P = 0.177) [Table 2].
|Table 2: Presence of TRI according to LN classification and activity index.|
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| Discussion|| |
In this study, the presence of TRIs in LN patients correlated with an increased AI or LN class. Since 1964, LN classifications were revised repeatedly until 1982, when a revised World Health Organization (WHO) classification was proposed. However, several problems with this classification system have been noted, primarily in Class III, in which segmental necrotic lesions are observed in more than 50% of the glomeruli and are associated with poor renal outcomes. In fact, the renal out-comes in this group are worse than in diffuse proliferative nephritis, WHO Class IV. 
The ISN/RPS 2004 classification introduced several modifications concerning quantitative and qualitative differences between the Class III and IV lesions, based on the glomerular pathology. Currently, the significant vascular and tubulo-interstitial pathologies are reported as separate entries. ,
According to the ISN/RPS 2004 classification, Class I is minimal mesangial LN with mesangial accumulation of immune complexes identified by immunofluorescence (or electron microscopy). Class II is mesangial proliferative LN. Activity is not measured in this class based on purely mesangial hyper-cellularity, and, thus, the presence of any active or chronic lesions is incompatible with Class II. Class III is focal LN, with both active and sclerotic lesions. Class IV is diffuse LN. In both Class III and Class IV, the parameters of activity and chronicity are defined. Class V is membranous LN with granular subepithelial deposits, and Class VI is advanced-stage LN with global glomerulosclerosis in >90% of the glomeruli. There is no evidence of active lesions in Class V and VI. 
In this study, 12 of 49 cases of LN had TRIs. Furthermore, most of the cases (9/35 or 25.7%) with TRIs were Class IV LN and five of the 12 cases with TRIs had an increased AI.
Although TRIs in LN are not specific, they indicate a Class IV LN and/or LN with an increased AI. This association is supported by the results of this study, which show significant correlations between an increased AI and Class IV LN. In fact, TRIs may not be associated with the earlier signs of lupus,  but rather more advanced cases.
These associations may be useful when we encounter cases of Class III and IV LN with inconclusive anti-dsDNA and C4 levels. It is unclear whether the associations that we observed between the presence of TRIs and Class IV LN and increased disease activity might affect a clinician's decision regarding the modality of the immunosuppressive therapeutic regimen to be administered. However, it is important for clinicians to report TRIs observed in lupus cases such that further investigations of their significance can be performed.
In conclusion, TRIs in LN are helpful in cases where the diagnosis of SLE is pending or not yet established. Although their presence is not a specific finding, TRIs significantly correlate with LN class and an increased AI. Larger studies are recommended to establish the relationships of TRIs with disease severity and LN classification as well as the value of TRIs in selecting a therapeutic regimen.
Conflict of interest: None.
This manuscript nor one with substantially similar content has not been published nor it is for publication elsewhere and all the data collected during the study is presented in this manuscript and no data from the study has been or will be published separately.
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Dr. Hala Kfoury
Department of Pathology (32), College of Medicine, King Saud University and King Khalid University Hospital, P. O. Box 2925, Riyadh 11461
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]