Catabolism of human γG-immunoglobulins of different heavy chain subclasses

Abstract

The rates of catabolism of human γG-immunoglobulins of subclasses γG₁, γG₂, γG₃, and γG₄ were studied by determining the rates of elimination from the circulation of pairs of ¹³¹I-and ¹²⁵I-labeled γG-myeloma proteins in 57 patients suffering from cancer other than multiple myeloma. On the average, γG₁-, γG₂-, and γG₄-myeloma proteins were catabolized at a rate similar to that of normal γG-immunoglobulin, whereas γG₃-myeloma proteins were catabolized more rapidly than normal γG-immunoglobulin. The average half-lives for the myeloma proteins were 12.3 days for normal γG, 11.6 days for γG₁, 12.4 days for γG₂, 8.2 days for γG₃, and 11.3 days for γG₄. However, significant differences in catabolic rates were observed when individual myeloma proteins of a single subclass were compared. These individual variations were present within all four heavy chain subclasses. The extent of differences ranged from 10 to 47%. The catabolic rate of normal γG was in an intermediate range when compared with myeloma proteins of relatively long and short half-lives. The rate of catabolism of an individual myeloma protein did not correlate with its light chain type, Gm factor, carbohydrate content, or electrophoretic mobility. These findings indicate that the structure(s) related to the catabolism of γG-immunoglobulins are complex and differ from one immunoglobulin molecule to another.