Determination of ligand binding capacity of soluble FcγRII and FcγRIII in sera of patients with SLE

Abstract

Background: Soluble, human low affinity Fcγ receptors, such as sFcγRII and sFcγRIII, are known to play a pathologic role in different diseases. Sandwich ELISAs had previously been applied for the specific detection and determination of these soluble receptors. In these ELISAs, commercial monoclonal antibodies (Ab) were used as capture antibodies with monoclonal or polyclonal antibodies serving as detector Abs. Increased levels of cell-free FcγRIII have been detected in patients with lupus but the functions and levels of sFcγRII have not been fully characterized yet.

Objectives: The aim of this work was to determine the ligand binding capacities and levels of soluble FcγRII and FcγRIII in sera of patients with systemic lupus erythematosus (SLE). Moreover, correlation between the levels of sFcγRII and sFcγRIII and the clinical activity of the disease were investigated.

Methods: Sera of 47 patients with SLE, and 51 healthy subjects were analyzed. In the newly developed indirect sandwich ELISAs commercial monoclonal anti-FcγRs are used as capture antibodies, and the ligand of FcγRII and FcγRIII, an artificial immune complex (IC), serves as a detection component replacing the second antibodies used in previous methods.

Results: The ligand binding capacity of both soluble FcγRII and sFcγRIII were elevated in the sera of SLE patients compared to control samples. This increase was significant in patients with the active disease (n = 30; p < 0.01). It was also revealed that a substantial part of the soluble Fcγ receptors in these patients was bound in vivo to circulating IC.

Conclusion: These newly developed ELISAs are probably more phisiologically relevant than other previous assays because they detect the circulating receptors on the basis their in vitro ligan binding capacities. Therefore this method can separately measure the levels of the soluble, free FcγRs and those bound circulating IC in vivo.

• Soluble Fcγ_it; receptors
• ligand binding
• systemic lupus erythematosus
• ELISA

Acknowledgements

This work was supported by grants from the Hungarian National Research Foundation (No. T034624 and T034696) and Research Group of Autoimmune Diseases, Hungarian Academy of Sciences.