Serum Soluble CD206 Complements Urinary Soluble CD163 in Detecting Active ANCA-Associated Glomerulonephritis

FSGS. HIV and ANA were negative. A subsequent testing for COVID nucleocapsid and spike protein was positive. Results of APOL1 genotype is pending. She was started on high dose steroids and followed up as an outpatient. Discussion: COVAN is increasing recognized as a serious complication of COVID. However, the typical presentation is in the setting of prominent respiratory involvement.

Background: PR3 is a major autoantigen in ANCA-associated vasculitis (AAV) and a neutrophil serine protease inhibited by alpha1-antitrypsin (AAT).Increased PR3 and decreased AAT were suggested as disease mechanism for PR3-but not MPO-AAV Methods: We assessed PR3 and AAT in 100 AAV patients and 50 healthy controls (HC) and produced recombinant wt-and mut-AAT to study the effect on proteolytic PR3 activity, membrane PR3 (mPR3) by flow cytometry and surface plasmon resonance (SPR), and neutrophil activation.
Results: In active PR3-and MPO-AAV, plasma PR3 concentration increased approximately 5-fold and plasma AAT 1.8-fold shifting the PR3:AAT ratio significantly towards PR3.Both parameters normalized with remission.Notably, only one PR3-AAV remission patient showed strongly decreased plasma AAT.The PR3 neutrophil content was approximately 50% higher in active PR3-and MPO-AAV accompanied by increased PR3 transcription.The resulting total PR3 pool (plasma PR3 concentration x plasma volume + neutrophil PR3 x neutrophil number) was approximately 3-fold larger in active AAV and normalized with disease remission.In active PR3-AAV but not MPO-AAV, the total PR3 pool correlated with kidney injury, hemoglobin, and PR3-ANCA ELISA.Membrane-PR3 (mPR3) correlated negatively with plasma AAT in HC, was increased in AAV patients with a compromised plasma AAT correlation.Mechanistically, extracellular AAT dose-dependently reduced mPR3 by competing with PR3 for the PR3-presenting CD177 receptor.Consequently, AAT reduced neutrophil activation by PR3-but not MPO-ANCA.Neutrophils from AAV patients and HC showed similar mPR3 reduction with AAT.However, in contrast to HC plasma, neutrophil incubation in active AAV plasma increased the AAT concentrations required to lower mPR3, an effect that was recapitulated by adding inflammatory mediators to HC plasma.Finally, oxidative AAT modification resulted in less PR3 interaction and diminished mPR3 reduction Conclusions: We found a strongly increased PR3 pool in active PR3-AAV and exclude decreased plasma AAT as the general underlying disease mechanism, as previously proposed.However, AAT controls mPR3 expression and subsequently PR3-ANCA induced neutrophil activation, suggesting adjunctive AAT administration may have beneficial effects in acute PR3-AAV Funding: Government Support -Non-U.S.

PO1417 Poster
Glomerular Background: Early detection of active glomerulonephritis (GN) in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is crucial to minimize renal damage, but accurate biomarkers are currently lacking.Urinary soluble CD163 (usCD163) has been shown as a potent biomarker for active ANCA GN.However, false negative rates can be as high as 29%.Here, we investigated whether serum soluble CD206 (ssCD206; macrophage mannose receptor), complements usCD163 in the detection of active ANCA GN.
Methods: Three independent cohorts (C1-Maastricht University Medical Center, C2-University Medical Center Groningen & C3-Trinity College Dublin) with available serum, urine, and renal biopsy samples (C1 only) were included.usCD163/creatinine (ng/mmol) and ssCD206 (ng/ml) were assessed by ELISA in urine and serum, respectively.The performance of usCD163 and ssCD206 to detect ANCA GN was assessed using receiver operating characteristics (ROC) curves.Biopsies from ANCA GN patients were immunohistochemically (IHC) stained for CD163 and CD206.Colocalization of CD163 and CD206 was assessed by immunofluorescence (IF).

Nephritis Serum Soluble CD206 Complements Urinary Soluble CD163 in Detecting Active ANCA-Associated Glomerulonephritis
Diseases: Immunology and Inflammation in Vasculitis and Lupus