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Macro creatine kinase: a study on CK-linked immunoglobulin
Insights
Creatine kinase (CK) linked to immunoglobulins, found in 0.8% of cases, can cause false-positive results in diagnostic tests. These CK-immunoglobulin complexes are distinct from other macro-CK forms.
Area of Science:
- Clinical Chemistry
- Immunology
- Biochemistry
Background:
- Creatine kinase (CK) is a crucial enzyme in energy metabolism.
- Macro-CK, including CK-immunoglobulin complexes, can interfere with diagnostic assays.
- Understanding CK-immunoglobulin complexes is important for accurate clinical interpretation.
Purpose of the Study:
- To characterize the prevalence and nature of CK-linked immunoglobulins.
- To investigate the diagnostic implications of these complexes.
- To differentiate CK-immunoglobulin complexes from other macro-CK entities.
Main Methods:
- Enzyme-immunofixation electrophoresis to identify CK-immunoglobulin complexes.
- Serum dissociation and re-formation studies at varying pH.
- Gel filtration and antibody inhibition assays.
- Urea and heat treatment to assess CK activity.
Main Results:
- CK-linked immunoglobulins were identified in 0.8% of cases studied.
- Heavy chains were consistently of class alpha, with lambda or kappa light chains.
- Complexes dissociated at pH 3.4 and reformed at pH 7.4.
- Residual CK-MM activity observed after urea/heat treatment, unlike normal CK.
- False-positive CK-B activity noted in immuno-inhibition tests.
Conclusions:
- CK-linked immunoglobulins represent a type of circulating immune complex.
- These complexes must be differentiated from other macro-CK forms.
- Their presence can lead to erroneous CK-B activity measurements, impacting clinical diagnosis.
Abstract:
We describe three cases in which creatine kinase (CK, EC 2.7.3.2) was linked to immunoglobulin in serum. In this study, its prevalence was 0.8%. Enzyme-immunofixation electrophoresis revealed that the heavy chain of CK-linked immunoglobulins was of class alpha in all cases. The light-chain type was identified as lambda in two cases and as both lambda and kappa in one case. The complexes were dissociated at pH 3.4 and re-formed with CK isoenzymes MM and MB at pH 7.4. The complex fraction obtained by gel filtration was not inhibited by anti-CK-M antibodies. Treatment of the serum with urea after heating shows residual CK-MM activity; in contrast, normal CK activity disappeared entirely after this treatment. The present study suggests that CK-linked immunoglobulins may be one of the circulating immune complexes and must be distinguished from other macro-CK in the strict sense. The results obtained show that the presence of the complexes results in false-positive CK-B activity in the immuno-inhibition test, and they may provide interesting insights into the mode of binding of the CK-linked immunoglobulins.