Isoelectric Focusing of Long-Acting Thyroid Stimulator Immunoglobulin G

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Abstract
Isoelectric focusing of long-acting thyroid stimulator immunoglobulin G [LATS-IgG] was used to determine the distribution of LATS activity among IgGs of various isoelectric points and to determine if isoelectric focusing techniques might yield LATS-IgG of increased biologic activity. LATS-IgG prepared from 16 LATS-positive sera was fractionated by isoelectric focusing [72 hr, 1200 V] using a 1% Ampholine solution, pH range 7.0 to 10.0. On the basis of absorbance at 280 nm, the effluent was gathered into 8 fractions. The 8 LATS-IgG subfractions and the parent IgG were tested in the same mouse bioassay. Following each of the 16 isoelectric focusing runs, maximal LATS activity was confined to one [6 instances] or two [10 instances] IgG subfractions [peak pi 8.99 ± 0.08 and 8.78 ± 0.09, respectively], with a 4- to 7-fold increase in LATS activity per mg protein compared to the parent IgG. However, of 12 LATS-negative Graves' disease IgGs submitted to isoelectric focusing, none of the IgG subfractions so derived showed LATS activity. Thus, while isoelectric focusing merits consideration as an approach to “purifying” LATS-IgG, it does not appear to offer a viable alternative to concentrating procedures to determine the incidence of circulating LATS in Graves' disease.

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