β₂‐Microglobulin‐containing IgG Complexes in Sera and Synovial Fluids of Rheumatoid Arthritis and Systemic Lupus Erythematosus Patients

Abstract

The occurrence and composition of complexed beta2-microglobulin (beta2m) in sera and synovial fluids of rheumatoid arthritis and systemic lupus erythematosus patients and control persons was investigated. Beta2m-containing complexes were detected in immune complex (IC)-enriched fractions isolated by precipitation with 3% polyethylene glycol 6000, in the macromolecular peaks after Sephadex G-200 gel filtration, and in IC desorbed from solid-phase Clq. Beta2m complexes were demonstrated also after precipitation of redissolved PEG-insoluble material by anti-human beta2m serum or isolation of the complexes by use of Sephadex-anti-beta2m. IgG was co-isolated with beta2m on Sephadex-anti-beta2m and free beta2m inhibited the binding of IgG to Sephadex anti-beta2m, indicating that IgG was present in the complexed beta2m. Analysis by SDS-polyacrylamide gradient electrophoresis under reducing conditions indicated that the purified beta2m complexes contained IgG and beta2m.

Serum Beta 2-Microglobulin/Cystatin C Index: A Useful Biomarker in Lupus Nephritis

“…We proposed the evaluation of Sβ2M/SCysC as a possible predictor of SLE activity in lupus nephritis since previous studies had shown increased Sβ2M in patients with active SLE [11, 12, 13, 14, 15, 16, 17, 18]. It is of note that such previous findings could be influenced by GFR, so we included a GFR level adjustment, using the ratios Sβ2M/ SCysC and Sβ2M SCreat.…”

“…High levels of serum β2M (Sβ2M) were described in rheumatoid arthritis, Sjögren's syndrome and SLE. β2M is catabolized by the kidneys, and there is a linear inverse correlation between levels of Sβ2M and glomerular filtration rate (GFR); its elimination is constant in normal people when its production is also constant [15]. Approximately 99.5% of β2M is freely filtrated by glomeruli and reabsorbed in renal proximal tubules.…”

“…Approximately 99.5% of β2M is freely filtrated by glomeruli and reabsorbed in renal proximal tubules. In the presence of renal dysfunction, β2M serum levels are increased when compared to those of patients with normal renal function [12, 13, 14, 15, 16]. …”

“…Some studies have previously failed to show a role for Sβ2M as a biomarker in SLE activity due mainly to its limited use in patients with renal involvement characterized by a reduction of the GFR [12, 13, 14, 15, 16, 17, 18, 19]. …”

Beta-2-Microglobulin-Derived Amyloid- Problems and Perspectives

“…(a) With respect to local enrichment it is of interest that higher Pint levels have been demonstrated in synovial fluids of patients with rheumatoid arthritis and SLE [28]. Fur thermore, P^m bears extensive homology to numerous molecules like the constant do main of immunoglobulin light chains, the T cell differentiation antigen, or the T cell anti gen receptor.…”