The circulating "atypical" lymphocyte.

Atypical lymphocytes have been observed in the peripheral blood of patients in a large number of clinical situations, including immune reactions to transplantation and immunization, collagen diseases and other autoimmune disorders, malignant disease, drug reactions, and infectious mononucleosis, as well as other bacterial and viral infections. These cells are readily identified by their increased size and the presence of active DNA synthesis. In morphology, they closely resemble lymphocytes transformed into blasts by exposure to mitogens or antigens in vitro. They vary in morphologic detail as well as surface marker characteristics, indicating that they comprise a heterogeneous mixture of cell types. These data suggest that atypical lymphocytes may represent a polyclonal immune response to antigenic stimulation.