Properties of Various Anti-γ-globulin Factors in Human Sera

The serological and physicochemical properties of the following three forms of human anti-gamma-globulin factors were compared: (a) rheumatoid factors; (b) Milgrom type anti-gamma-globulin factors; and (c) factors directed against an antigen in human gammaG-globulin that is hidden in the intact molecule and revealed by enzymatic digestion at low pH. The property common to these factors is ability to interact with human gammaG-globulin; they are distinguishable because they react with different antigenic groups on this molecule. In all of five sera, the Milgrom type anti-gamma-globulin factors were gammaM-globulins. They reacted with various human gammaG-globulin antibodies but failed to interact with gammaM-globulin type antibodies in agglutination and absorption experiments. When isolated from other anti-gamma-globulin factors, they agglutinated red cells coated with intact anti-Rh antibodies, but failed to react with cells cells coated with pepsin-digested anti-Rh antibody. These observations indicate that the agglutinator reacts with the crystallizable, inert fragment of gammaG-globulin. Anti-gamma-globulin activity directed against an antigen in human gammaG-globulin revealed by pepsin digestion was demonstrated in gammaG-, gammaA-, and gammaM-globulins. This anti-gamma-globulin factor could be absorbed by antigen-antibody precipitates containing human antibody, which shows that the hidden antigen in human gammaG-globulin is revealed not only by enzymatic digestion at low pH, but also when gammaG-globulin is present as antibody in an antigen-antibody precipitate. Rheumatoid factors and Milgrom type anti-gamma-globulin factors were also absorbed by antigen-antibody precipitates containing human antibody. The results indicate that the three distinct forms of antigamma-globulin factors may all be produced as a result of antigenic stimulation by autologous antigen-antibody complexes.