Observations on Certain Sero- Logical and Physical Features of Cold Agglutinins in Cases of Primary Atypical Pneumonia and of Hemolytic Anemia

Some of the properties of cold agglutinins in certain human sera have been listed in a recent review (1). The knowledge concerning these properties is based on studies of the phenomenon by various methods in serum or plasma from isolated cases of a large variety of conditions. With respect to the cold agglutinins in cases of primary atypical pneumonia, limited studies of certain aspects were reported in 1918 (2) in one case of atypical bronchopneumonia, in 1938 (3) in a similar case, and recently (4) in a few cases which more closely resemble those of primary atypical pneumonia of unknown etiology with which we have been concerned in the previous papers of this series. In the course of serological studies of cases of atypical pneumonia beginning in the fall of 1942, a number of observations were made on certain features of the cold agglutinin reaction and on the methods used for demonstrating and titrating these agglutinins. Circumstances did not permit extensive and complete studies of all the aspects of this reaction which were contemplated. A number of the observations that were made are of sufficient interest, however, to warrant a presentation of the results at this time, even though some of them are only of a preliminary nature. The investigations which are reported in this paper deal with two broad categories: (1) some serological properties of the cold agglutinins, particularly their relation to the human group isoagglutinins and to cold agglutinins for erythrocytes of other animals, and (2) certain physical properties of the cold agglutinins. Data concerning certain features of the technique are presented in the paper which follows.