A DECREASE IN REACTIVE DISULFIDE BONDS OF SERUM IGG SIGNALS A CHARACTERISTIC CHANGE IN THE IGG SUBCLASS PATTERN OF RATS BEARING EXPERIMENTAL-TUMORS

Previous studies have shown that human IgG1 contains a 'reactive' disu lfide Reactive disulfides bridge (SS), reaction, and that the serum l evel of this IgG subclass is selectively diminished in patients with v arious malignant diseases. Here we present evidence that in rats IgG2b is the only subclass that carries one SS per molecule. Furthermore, it is shown that rats inoculated with experimental tumor lines, i.e., the Yoshida hepatoma ascites tumor and the Walker 256 carcinosarcoma g rowing in ascites or as solid tumor, exhibit significantly decreased S S per mole IgG which corresponds to a selective diminution of IgG2b. Although at later stages there is a quantitative correlation with the tumor burden, with the Walker tumor this effect becomes significant as early as 24 h after inoculation, i.e., well before exponential tumor growth and an absolute reduction of total IgG. Control animals injecte d intraperitoneally with either viable spleen cells or irradiated Walk er 256 cells did not show comparable alterations in their IgG subclass profile. Thus, the selective defect of IgG2b requires the presence of viable and proliferating tumor cells. Possible mechanism(s) of tumor- associated shifts in IgG subclasses are discussed.