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Background and Aims

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is caused by autoantibodies against the blood enzyme ADAMTS13. We showed that patients with acute iTTP have an open ADAMTS13 conformation, while healthy donors (HD) and 78% of iTTP patients in remission with a normal ADAMTS13 activity (TS13:act; >50%) have a closed ADAMTS13. However, the cause of the open ADAMTS13 conformation, as well as the ADAMTS13 conformation in iTTP patients in remission with TS13:act <50% is unknown. Therefore, we investigated whether anti-ADAMTS13 autoantibodies induce conformational changes in ADAMTS13 and also determined the ADAMTS13 conformation in iTTP patients in remission with TS13:act <50%.

Methods

Purified IgG’s from 18 acute iTTP samples were added to folded ADAMTS13 from HD and tested for ADAMTS13 conformation. Additionally, ADAMTS13 conformation was determined in 166 iTTP samples from remission phase.

Results

Closed ADAMTS13 in HD plasma was opened by addition of purified IgGs from 14 of the 18 (78%) acute iTTP plasmas, demonstrating that patient anti-ADAMTS13 autoantibodies can induce a conformational change in ADAMTS13. Further, ADAMTS13 was closed in 62% (56/91) of the remission samples with TS13:act >50%, confirming our previous results. Interestingly, ADAMTS13 was open in 95% (71/75) of remission samples with TS13:act <50%.

Conclusions

We showed that anti-ADAMTS13 autoantibodies cause a conformational change in ADAMTS13 in iTTP. Additionally, we found that besides acute iTTP patients, also the majority (106/166) of iTTP patients in remission have an open ADAMTS13 conformation, indicating that the underlying pathophysiology is still ongoing. Therefore open ADAMTS13 could be used as a biomarker for subclinical disease during iTTP monitoring.

Background and Aims

Heat shock protein 70 (HSP-70) is an important part of the intracellular defense system and provide an important immunoregulatory function. Failure of this function may occur in chronic glomerulonephritis (CGN).

Aim was to evaluate HSP70 levels in the urine and renal tissue and the anti-HSP70 antibody levels in CGN.

Methods

76 patients with CGN patients were included: 10 patients with mild proteinuria (<1.0 g/day) and 10 healthy subjects. 34 active CGN with proteinuria >1.0g/day (I group), 42 with nephrotic syndrome (II group). Urinary levels of HSP70, IL10, and serum levels of anti-HSP70 were measured by ELISA. The immunohistochemical peroxidase method was used to study the expression of HSP70 and Foxp3+ in kidney biopsies.

Results

Median urinary HSP70 levels in patients with nephrotic syndrome (NS) group II and group I were higher than in positive and negative controls. Hsp-70 levels in the urine in group II - significantly higher than in group I. HSP70 expression index in tubular cells positively correlated with urinary HSP70 and proteinuria. The number of Treg ^Foxp3+ cells in the kidney interstitium and interleukin-10 excretion were decreased in patients with NS. Anti-HSP70 antibodies serum levels in patients of group II and group I were significantly higher than in positive and negative controls.

Conclusions

Hsp70 urinary and tissue levels increased in patients with active CGN. However, activation of HSP70 did not lead to an increase in tissue levels of Treg^Foxp3+ cells or release of IL-10. These data may indicate an impaired anti-inflammatory function of HSP70 in patients with a severe nephropathy.

Background and Aims

Apoliprotein E4 (apoE4) is the strongest genetic risk factor for Alzheimer’s Disease although the detailed method of action is still unclear. Kim et al (JEM 209, 2149) demonstrated that a monoclonal anti-apoE4 antibody reduced the amyloid deposition in an AD mouse model. These data prompted us to investigate human plasma and the intravenous immunoglobulin G (IVIG) preparation Gammagard Liquid (GGL) for the presence of naturally occurring anti-apoE4 immunoglobulin G (IgG) antibodies.

Methods

A direct ELISA with purified human apoE4 (Sigma) was used for the detection of anti-apoE4 IgG in a human reference plasma pool and several lots of GGL. The binding of natural occurring anti-apoE4 IgGs was compared with that of a monoclonal and a polyclonal anti-apoE4 preparation. Binding specificity was checked by competition studies using purified apoE4, apoE3 and apoE2.

Results

Human plasma and GGL contain anti-apoE4 IgG with EC₅₀ binding values in the low one-digit µg/mL range. Binding to plate-bound apoE4 was shown to be specific as it could be dose-dependently inhibited by apoE4 in solution and by a monoclonal anti-apoE4 antibody. In contrast, purified apoE2 and apoE3 did not dose-dependently compete with binding of anti-apoE4 IgG to apoE4 suggesting the presence of conformation-specific antibodies specifically targeting apoE4.

Conclusions

Specific human naturally occurring anti-apoE4 IgGs, described to our best knowledge in plasma and IVIG for the first time, add to the list of rare examples that also naturally occurring IgG antibodies can be endowed with specific binding to conformationally different forms of proteins.