The relationship between rheumatoid factors and serum agglutinators.

A detailed study of the DEAE fractionated serum R. W. [anti-Gm(x)] has revealed differences in specificity between the 7S serum agglutinators of erythrocytes sensitized with anti-Rh antibodies digested with proteolytic enzymes and 19S rheumatoid factor monospecific for Gm(x). The serological reactivity and specificity of the serum agglutinators is determined by the enzymatic modification of the globulin molecules and is unrelated to the Gm type. On the other hand, the 19S rheumatoid factor [anti-Gm(x)] is reactive with undigested molecules or with those antibody molecules digested with proteolytic enzymes which leave the Fc piece intact. The 19S factor specificity is otherwise unrelated to digestion of the globulin molecule and rests solely on the intactness of the Gm site for which it is specific.