LOCALIZATION OF THE IMMUNOGLOBULIN FACTORS Gm(a), Gm(b) AND Gm(x) IN LYMPHOID TISSUE OBTAINED FROM AN INDIVIDUAL OF Gm ax/ab GENOTYPE

Summary The immunoglobulin markers Gm(a) and Gm(b) were localized by fluorescent antibody in separate populations of plasma cells in the medullary cords of a lymph node obtained from a Melanesian of Gm ax/ab genotype. Gm(x) was always found in the same cells as Gm(a), although Gm(a) also occurred alone. It is suggested that Gm(a) and Gm(b) are coded by separate, although closely associated, cistrons with separate regulator genes. In individuals possessing Gm ab the cistrons are on the same chromosome; in Caucasian populations which possess Gm a and Gm b they are not.