Immune complex clearance by complement receptor type 1 in SLE.

Patients with systemic lupus erythematosus (SLE) have relative deficiencies of the C3b/C4b receptor (CR1, CD35) on erythrocytes (E). This receptor takes part in the binding, transport and endocytosis of circulating immune complex bound complement components (ICC). Besides the autoantibodies the abnormalities in IC elimination are fundamental to the pathogenesis of SLE. During the last 15 years more than 100 patients with SLE have been treated in our Department and their data on ICC clearance by ECR1 analyzed. After plasmapheresis the ECR1 expression and also the binding sites for ICC were increased, while the level of IC and autoantibodies were reduced. Stimulating erythropoiesis in patients with anaemia and lupus nephritis caused the decreased expression and functional activity of ECR1 to be improved. In patients with SLE the level of soluble CR1 was also decreased, but a significant portion of soluble CR1 bound ICC in vivo, especially in those with severe renal lesion.

Immune complex clearance by monocytes and macrophages in systemic lupus erythematosus.

During the last 30 years more than 700 patients with systemic lupus erythematosus (SLE) have been treated in our department with their data analyzed. Here we focus on circulating immune complex (CIC) and its clearance. We demonstrated, microscopically, that the uptake of IgG sensitized erythrocytes (EA), via monocytes (Mo) of SLE patients, was elevated and correlated with the high CIC content. The in Vivo clearance of sensitized autolog E, and the in vitro degradation rate of soluble IC by Mo of SLE patients were decreased. This discrepancy could be explained by the molecular heterogeneity of FcgammaR being recognized lately. The high FcgammaRI expression and the low FcgammaRII and FcgammaRIII expression were detected by monoclonal antibodies (mAb) on Mo in SLE. The EA bound mostly to FcgammaRI, FcgammaRII and FcgammaRIII have a role in phagocytosis. The decreased receptor expression and function correlated with the disease activity and renal involvement. The shedding of receptors may cause a decrease on Mo surface, with the soluble FcRII and FcgammaRIII levels being elevated in serum of SLE patients. The mannose binding receptors, which play a role in the phagocytosis of apoptotic cells in SLE, were also decreased on Mo of SLE patients.

Determination of ligand binding capacity of soluble Fc gamma RII and Fc gamma RIII in sera of patients with SLE.

BACKGROUND: Soluble, human low affinity Fcgamma receptors, such as sFcgammaRII and sFcgammaRIII, 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 FcgammaRIII have been detected in patients with lupus but the functions and levels of sFcgammaRII have not been fully characterized yet. OBJECTIVES: The aim of this work was to determine the ligand binding capacities and levels of soluble FcgammaRII and FcgammaRIII in sera of patients with systemic lupus erythematosus (SLE). Moreover, correlation between the levels of sFcgammaRII and sFcgammaRIII 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-FcgammaRs are used as capture antibodies, and the ligand of FcgammaRII and FcgammaRIII, 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 FcgammaRII and sFcgammaRIII 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 Fcgamma 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 FcgammaRs and those bound circulating IC in vivo.

Possible role of factor XIII subunit A in Fcgamma and complement receptor-mediated phagocytosis.

Besides its traditional role in hemostasis, factor XIII subunit A (FXIII-A) is supposed to function as a cellular transglutaminase and to be involved in certain intracellular processes, including cytoskeletal remodeling. To investigate its intracellular role, the aim of the present study was to follow changes in FXIII-A production in combination with the receptor-mediated phagocytic activities of monocytes/macrophages and to examine the phagocytic functions of monocytes in patients with FXIII-A deficiency. Human blood monocytes were isolated from the buffy coats of healthy volunteers and cultured for 4 days. The FcgammaR-mediated phagocytosis of sensitized erythrocytes (EA) and the complement receptor (CR)-mediated phagocytosis of complement-coated yeast particles were studied during monocyte/macrophage differentiation. Changes in the gene expression of FXIII-A were detected by real-time quantitative RT-PCR. FXIII-A protein production was investigated with fluorescent image analysis at single cell level and Western immunoblot analysis. Both the FcgammaR and CR-mediated phagocytosis increased during culturing, which peaked on day 3. The phagocytic activity of the cells could be markedly inhibited with monodansylcadaverine, an inhibitor of the transglutaminase-induced crosslinking of proteins. The phagocytosis of EA, complement-coated and uncoated yeast particles was found to be strongly diminished in monocytes of FXIII-A deficient patients. The phagocytic functions of cultured cells showed a change in parallel with the alterations in FXIII-A mRNA expression, as well as with that in FXIII-A in protein synthesis detected by image and Western immunoblot analyses in concert. Our results suggest that FXIII-A plays a role in the Fcgamma and complement receptor-mediated phagocytic activities of monocytes/macrophages.