Circulating prostatic acid phosphatase-immunoglobulin complexes in Sjogren's syndrome

Electrophoretic analysis of enzyme-linked immunoglobulins and their clinical significance

The appearance of circulating enzyme-linked immunoglobulin complexes (E-Ig) is common for most enzymes used in clinical biochemical tests. The presence of E-Ig may result in altered enzyme activity in serum and interfere with the measurement of isoenzymes, and is thus of diagnostic importance. E-Ig can be identified by confirming that the binding protein is an immunoglobulin by its reaction with specific anti-human immunoglobulin antibodies. Currently, the presence of E-Ig in an individual is regarded as a benign phenomenon, not indicative of any particular disease process. However, it is becoming clear that E-IgG are closely associated with autoimmune states.

Chromatographic and electrophoretic studies of circulating immune complexes in plasma

The protein nature of soluble immune complexes from fresh plasma was studied by combining several analytical biochemical techniques. Free immunoglobulins (Ig) G were separated from larger immune complexes by gel permeation chromatography. In a second step, immune complexes, free IgA and IgM were isolated by protein-A and protein-G affinity chromatography and analysed by two-dimensional gel electrophoresis. Sixteen plasma samples from healthy donors were analysed and evaluated visually. Their protein profiles on the gels turned out to be similar, showing only slight quantitative differences. In one case, additional proteins were detected. To prove the ability of the method, immune complexes were analysed from four plasma samples that showed macro creatine kinase type 1, a complex formation between creatine kinase BB and IgG. This methodology can be used for the examination of immune complexes of unknown protein composition in serum or plasma.

Detection of macroenzymes in serum by high-performance gel permeation chromatography

A rapid high-performance gel permeation chromatographic method to confirm the presence of enzymes with abnormally high relative molecular masses (macroenzymes) in serum is described. The technique requires 200 microliters of serum, can be automated and has been implemented for the analysis of creatine kinase (CK), lactate dehydrogenase, amylase, and alkaline phosphatase (ALP) activities. Serum fractionation according to relative molecular mass is completed within 21 min, and 84-106% of enzyme activities are recovered in the eluted fractions. The elution patterns obtained make possible the differentiation of 40 samples containing at least 10 U/l immunoglobulin-enzyme complexes, aggregated mitochondrial CK or membrane fragments carrying ALP activity from 40 control samples without these high-mass enzyme forms.

A circulating complex between ASAT and IgG in serum in an apparently healthy woman

An elevated level of serum aspartate aminotransferase (ASAT) activity in a subjectively healthy woman was shown to be due to circulating ASAT:IgG complexes. The complexes were demonstrated by taking advantage of the specific interaction between protein A and IgG. Thus, greater than 90% of the patient's ASAT activity in serum could be bound to protein A-Sepharose demonstrating that nearly all the patient's serum ASAT was complexed to IgG. The ASAT-binding capacity of patient serum was calculated as approximately 850 micrograms ASAT/l which corresponds to about 0.01% of patient's IgG.