A quantitative ultrastructural study of peripheral blood lymphocytes containing parallel tubular arrays in Epstein-Barr virus and cytomegalovirus mononucleosis.

In the normal peripheral circulation there exists a subpopulation of lymphocytes that is ultrastructurally distinct. This lymphocyte is identified with the electron microscope by the presence of cytoplasmic microtubulelike inclusions called parallel tubular arrays (PTAs) and contains Fc-receptors for cytophilic antibody. In this study, lymphocytes containing PTAs (PTA-lymphocytes) were quantitated from serial peripheral blood specimens obtained from two patients with Epstein-Barr virus (EBV) mononucleosis and two patients with cytomegalovirus (CMV) mononucleosis. These data were then correlated with the clinical state of the patient. It was determined that both the percentage and absolute number of PTA-lymphocytes were highest during the acute phase of the illness. In follow-up specimens, three of the four patients' absolute lymphocyte count fell to within normal limits before the absolute PTA-lymphocyte count. In one patient, the absolute PTA-lymphocyte count was significantly elevated 13 months after the initial clinic visit. Although the PTA-lymphocyte count was highest during the acute phase of the illness, there was no consistent correlation with the clinical state of the patient during follow-up. The estimation of absolute PTA-lymphocyte counts was determined to be valid after a morphometric analysis of the cellular areas occupied by PTAs during the acute and convalescent phases of the disease revealed no statistical differences. Electron microscopy was also performed on the peripheral blood of a patient with syphilis. Although a hematologic workup of this patient during the acute phase of his illness revealed a large number of atypical lymphocytes, electron-microscopic examination of the same specimen revealed both a normal number and a normal percentage of PTA-lymphocytes. The immunologic role of this ultrastructurally distinct third population (non-T, non-B) of lymphocytes, or "killer cells," in the course of infectious mononucleosis is discussed.