Three groups of proteins have been classified as immune globulins. They are:
γ2-globulins, which have a molecular weight of approximately 150,000, a sedimentation constant of 7S, and are known to contain most of the antibodies to viral and bacterial antigens,
γ1A-globulins, known also as B2A-globulins, which have a molecular weight of approximately 150,000 and a sedimentation constant of 7S,
γ1M-globulins, known also as B2M-globulins, which have a molecular weight of approximately 1,000,000, a sedimentation constant of 19S, and are known to contain a number of antibodies including the isohemagglutinins, heterophil antibodies, and typhoid 0 agglutinins.
HUNTLEY CC, LYERLY A. Immune Globulin Determinations in Allergic Children. Am J Dis Child. 1963;106(6):545-552. doi:10.1001/archpedi.1963.02080050547003