Heterogeneity of cold haemagglutinins.

All of seven sera with high titre cold agglutinins agglutinated rabbit red cells at 4° to similar titres as were recorded with human red cells. At 20° all the sera showed almost optimal activity against rabbit red cells, while the activity against human red cells was very weak. Two of the sera agglutinated rabbit red cells as strongly at 37° as at lower temperatures.

PROPERTIES OF VARIOUS ANTI-GAMMA-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.

STUDIES OF THE ANTIBODY NATURE OF THE RHEUMATOID FACTOR. REACTION OF THE RHEUMATOID FACTOR WITH SHEEP ERYTHROCYTES SENSITIZED WITH HUMAN ANTI-SHEEP CELL ANTIBODIES AND WITH O RH POSITIVE CELLS SENSITIZED WITH INCOMPLETE ANTI-RH ANTIBODIES.

The reaction of the rheumatoid factor (RF) with 7S γ-globulin antibodies of nine persons immunized with sheep erythrocytes was studied. All of a panel of rheumatoid sera with high Waaler-Rose titres agglutinated sheep cells sensitized with the human anti-sheep cell antibodies and O Rh positive cells sensitized with the `diagnostic' anti-CD serum Ripley. The RF measurable with these systems could be absorbed to diphtheria toxoid—human antitoxin precipitate, whereas the absorption with egg albumin—rabbit anti-egg albumin precipitate did not result in any appreciable titre reduction.