Demonstration of Gm 1(a) and Anti-Gm 1(a) Specificities by Tanned Cells Coated with Individual γ-Globulins

Abstract

The detection of rheumatoid factors by human Rh_o cells coated with incomplete Rh_o antibody is based on a reaction determined by the genetic (Gm) specificity of the 7 S γ-globulin coating the cells. Both pooled human γ-globulin (Cohn Fraction II) and rabbit γ-globulin lack this specificity and thus are unable to distinguish the anti-Gm specificities of the several rheumatoid factors. The present study demonstrated that 7 S γ-globulins isolated from normal human sera by chromatographic techniques and coated on tannic acid-treated sheep erythrocytes retain their Gm specificity. The Gm 1(a) character of several sera and their 7 S γ-globulin fractions and the anti-Gm 1(a) specificity of several rheumatoid sera were established by correlating the inhibitory capacity of a panel of sera with their Gm 1(a) positivity or negativity as established by the sensitized D cell test. Heating the isolated γ-globulin to 56°C before coating cells was usually necessary to provide test cells with Gm specificity, whereas preheating the γ-globulin to 63°C destroyed Gm specificity. A major limitation of the Gm test system is the scarcity of anti-Rh_o sera capable of distinguishing rheumatoid factors of various anti-Gm specificities. The described system eliminates the need for anti-Rh_o sera of Gm 1(a+) phenotype and permits the Gm 1(a) classification of normal sera, as well as the detection of rheumatoid factor of anti-Gm 1(a) specificity.