METABOLISM OF IGE STUDIES IN NORMAL INDIVIDUALS AND IN A PATIENT WITH IGE MYELOMA

Abstract

IgE [immunoglobulin E] metabolic turnover studies with purified radioiodinated IgE were performed in normal individuals and in a patient with IgE myeloma. The validity of the turnover studies was established in several ways, including comparisons of radioiodinated IgE turnover with the turnover of endogenously labeled 14C-IgE, and with the turnover of infused unlabeled IgE in a patient with hypogammaglobulinemia. The geometric mean serum IgE concentration in 73 normal adults was 96 ng/ml with a 68% confidence interval of 24-386 ng/ml. Metabolic turnover studies in 10 control individuals disclosed a geometric mean total circulating IgE of 4.1 .mu.g/kg, a mean percentage of the total exchangeable IgE in the intravascular space of 41%, a mean half-time of survival of IgE of 2.7 days, a mean fractional catabolic rate of 94% of intravascular pool per day and a geometric mean synthetic rate of 3.8 .mu.g/kg per day. IgE has the lowest synthetic rate and highest fractional catabolic rate of the 5 major classes of Ig molecules. A patient with IgE myeloma had a serum IgE concentration of 42 mg/ml, a total circulating IgE of 1.7 g/kg, and a synthetic rate of 270 mg/kg per day. Although the synthetic rate was vastly increased, the survival time was prolonged and the fractional catabolic rate was decreased to 5.1 days and 16-22% of the intravascular pool per day, respectively. IgE is apparently catabolized in part by a mechanism common to all Ig classes and in part by a unique mechanism not available to other Ig. At very high IgE serum concentrations, such as those encountered in patients with IgE myeloma, the unique mechanism would be saturated and only the catabolic pathways available to all Ig would be available to IgE.