B lymphocyte subpopulations in chronic lymphocytic leukemia.

We have defined two subpopulations of B lymphocytes in chronic lymphocytic leukemia (CLL). The major variant (termed typical) was characterized by the presence of a relatively homogeneous population of small-to-medium-sized lymphocytes with low-density SmIgM and no evidence of intracellular Ig synthesis. A minor group (termed atypical) was identified by the presence of a pleomorphic cell population with few small lymphocytes. The predominant SmIg was IgG, which was detected intracellularly as well as in the serum. The atypical group appeared to be an arrest at a later stage of differentiation where a switch from IgM to IgG synthesis and secretion had occurred. Clinical correlation suggested several clear-cut differences in clinicopathologic characteristics, but the median survivals for both groups at 2 yr was nearly identical.