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A calcium-dependent cryoglobulin IgM kappa/polyclonal IgG
M Qi1, G Steiger, J A Schifferli
1Laboratory of Immunonephrology, University of Geneva, Switzerland.
Journal of Immunology (Baltimore, Md. : 1950)
|October 1, 1992
Summary
Calcium (Ca) and cold temperatures induce polymerization of IgM kappa/IgG complexes, explaining cold-induced precipitation in mixed cryoglobulins. This finding clarifies mechanisms in Sjögren's syndrome.
Area of Science:
- Immunology
- Biochemistry
- Rheumatology
Background:
- Cold-induced precipitation of mixed cryoglobulins is poorly understood.
- Mixed cryoglobulins, particularly type II IgM kappa/IgG, are implicated in autoimmune diseases like Sjögren's syndrome.
- Investigating the specific mechanisms of cryoprecipitation is crucial for understanding disease pathogenesis.
Purpose of the Study:
- To elucidate the mechanisms behind cold-induced precipitation of a specific type II mixed cryoglobulin (IgM kappa/IgG) from a Sjögren's syndrome patient.
- To determine the role of calcium ions (Ca) and temperature in the cryoprecipitation process.
- To analyze the interaction between IgM kappa and IgG components under varying conditions.
Main Methods:
- Studied a patient's mixed cryoglobulin (IgM kappa/IgG) precipitation in serum and in the presence of EDTA.
- Assessed cryoprecipitation with various divalent cations (Ca, Ba, Mn, Sr, Mg, Co).
- Investigated the effect of calcium on purified IgM kappa and IgM kappa/IgG complexes using radiolabeled calcium (45Ca) and affinity measurements ([125I]IgM kappa).
- Analyzed the temperature-dependent affinity of IgM kappa for IgG via sucrose density gradient ultracentrifugation.
Main Results:
- Cryoprecipitation required calcium (Ca) and was optimal at 1 mM free Ca, and also induced by Ba, Mn, and Sr.
- Purified IgM kappa/IgG complexes precipitated with Ca, but IgM kappa alone did not.
- Calcium did not directly bind to cryoglobulins or alter the affinity between IgM kappa and IgG.
- IgM kappa/IgG complex affinity increased significantly at 4 degrees C compared to 37 degrees C.
Conclusions:
- Cold-induced precipitation of this mixed cryoglobulin involves two steps: temperature-dependent immune complex formation and calcium-induced polymerization.
- Calcium acts as a crucial cofactor, promoting polymerization of soluble IgM kappa/IgG complexes at lower temperatures.
- These findings provide a mechanistic insight into cryoglobulin precipitation in Sjögren's syndrome.
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