Tubuloreticular Inclusions in the Absence of Systemic Lupus Erythematosus and HIV Infection: A Report of Three Pediatric Cases

An Interesting Case of Nonlupus Full-House Nephropathy

Full-house immunofluorescence and endothelial tubuloreticular inclusions are known as characteristic features of lupus nephritis. However, both features are not pathognomonic for lupus nephritis. A kidney biopsy specimen showing full-house immunofluorescence pattern in the absence of autoantibodies and classical clinical features of Systemic Lupus Erythematosus (SLE) is now considered as nonlupus full-house nephropathy (FHN). Nonlupus FHN may be idiopathic or due to other disease processes known as secondary nonlupus FHN. Here, we report the case of a 36-year-old female who presented with nephrotic proteinuria with bland urine sediment. Additional analyses revealed normal serum antinuclear antibody (ANA), normal anti-double-stranded DNA (anti-dsDNA) antibodies, and normal serum C3 and C4 levels. A renal biopsy showed a normal-appearing glomerulus without any proliferation or capillary wall thickening and widespread glomerular immune deposits (full-house effect; IgA, IgG, IgM, C3, and C1Q) on direct immunofluorescence. Renal electron microscopy showed diffuse effacement of visceral epithelial cell foot processes and mesangial electron dense deposits. The patient was diagnosed as nonlupus FHN. There is a controversial role of steroids and other immunosuppressive drugs in the treatment of nonlupus FHN patients, but our case patient responded favourably to steroid therapy. The term nonlupus FHN can be used as an umbrella term for patients who do not satisfy the clinical and serological criteria of SLE.

The Role of Membranes and Lipid-Protein Interactions in the Mg-Branch of Tetrapyrrole Biosynthesis

Chlorophyll (Chl) is essential for photosynthesis and needs to be produced throughout the whole plant life, especially under changing light intensity and stress conditions which may result in the destruction and elimination of these pigments. All steps of the Mg-branch of tetrapyrrole biosynthesis leading to Chl formation are carried out by enzymes associated with plastid membranes. Still the significance of these protein-membrane and protein-lipid interactions in Chl synthesis and chloroplast differentiation are not very well-understood. In this review, we provide an overview on Chl biosynthesis in angiosperms with emphasis on its association with membranes and lipids. Moreover, the last steps of the pathway including the reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), the biosynthesis of the isoprenoid phytyl moiety and the esterification of Chlide are also summarized. The unique biochemical and photophysical properties of the light-dependent NADPH:protochlorophyllide oxidoreductase (LPOR) enzyme catalyzing Pchlide photoreduction and located to peculiar tubuloreticular prolamellar body (PLB) membranes of light-deprived tissues of angiosperms and to envelope membranes, as well as to thylakoids (especially grana margins) are also reviewed. Data about the factors influencing tubuloreticular membrane formation within cells, the spectroscopic properties and the in vitro reconstitution of the native LPOR enzyme complexes are also critically discussed.

The importance of tubuloreticular inclusions in lupus nephritis

Tubuloreticular inclusions (TRI) are distinctive cytoplasmic structures of unknown origin that typically associate with autoimmune and viral diseases. We investigated the clinical and prognostic relevance of TRI detection in patients with lupus nephritis (LN). We conducted a single centre study of patients (n=84) with biopsy evidence of LN. Clinical variables included demographics, SLEDAI score, and autoantibody profiling; while histological evaluation included TRI presence, International Society of Nephrology/Renal Pathology Society (ISN/RPS) classification with NIH activity and chronicity indices, immunofluorescence, and other EM findings. Patients with and without TRI were compared by non-parametric statistical methods and survival analysis for the endpoints of death and renal failure. TRI were detected in 37 patients (44%) that were younger (28.4 vs 34.3 years, p=0.02) and more often from Asian background (37.8% vs 19.1%, p=0.04) compared to patients without TRI. SLEDAI score (11 vs 12 units, p=0.36) and amount of proteinuria (370 vs 340 mg/mmol, p=0.71) were similar in both groups; however, TRI positive patients had increased frequency of anti-SSB antibodies (16% vs 2%, p=0.02), 'full house' immune complex deposition (85% vs 58%, p=0.04) and subendothelial electron dense deposits (83% vs 65%, p=0.07), but were less often anti-dsDNA Ab positive (62% vs 85%, p=0.02). Patient and renal survival were not influenced by TRI status. TRI were observed in nearly half of all LN patients and TRI positive patients more often carried anti-SSB antibodies. However, TRI had little bearing on disease presentation or outcome in LN.

The histological spectrum of tubulo-reticular inclusion positive renal biopsies: a tertiary hospital experience and review of the literature

AIM

To identify the underlying diseases with TRI-positive kidney biopsies, and describe the histological pattern and spectrum of TRI-positive kidney biopsies.

METHODS

A retrospective analysis of all patients' chart that underwent renal biopsy at King Saud University Medical City between 2012 and 2017 was done. Kidney biopsies that indicated a positive result for tubuloreticular inclusions (TRI's) on electron microscopy were reviewed and the underlying disease and histological pattern was extracted.

RESULTS

Of 1,473 native kidney biopsies reviewed, 96 (6.5%) were TRI-positive. Of the 96 TRI-positive kidney biopsies, 87 (90.6%) were TRI-positive lupus nephritis (LN); of which 10 (11.5%) were Class V, 49 (56.3%) were active LN, and 28 (32.2%) were inactive LN. The underlying diseases of the nine non-LN TRI-positive cases included diabetic nephropathy, connective tissue disorders, immune complex mediated Glomerulonephritis (GN), acute thrombotic microangiopathy, rhabdomyolysis, and Wegener's disease.

CONCLUSION

LN is a very common finding in TRI-positive kidney biopsies. Active LN and chronic LN are the more common classes of TRI-positive LN kidney biopsies, than pure membranous (Class V) LN. TRI positive kidney biopsies without LN are commonly found in diabetic nephropathy, connective tissue disorders and immune mediated GN's. This study highlights this finding in our patients cohort in opposition to what has been reported in the literature.