Natural killer cell surface markers on cells containing parallel tubular structures.

Parallel tubular structures (PTS) and/or the associated electron-dense granules, thought to contain molecules responsible for target cell lysis, can be detected in the cytoplasm of lymphocytes with large granular lymphocyte (LGL) morphology. In the present study we compared PTS presence in freshly isolated peripheral blood lymphocytes and peripheral blood lymphocytes incubated overnight in the presence of human pooled serum, sera from patients with Hodgkin's disease and interferon-alpha. Under all conditions we found PTS in the majority of CD16+ cells (64.3-74.8%) but less than 41.8% in CD57+ cells. In the case of double-labeled lymphocytes, 41.0-61.7% CD16+/8+ but only 24.2-27.5% CD57+/8+ cells were PTS+. Thus, in all cases where lymphocytes expressed CD16 antigen there was a high percentage of PTS positivity. Although the PTS+ cells exhibited phenotypic heterogeneity there was, except for a proportion of CD57+ lymphocytes which exhibited less of the characteristic LGL features, generally LGL morphological homogeneity. CD16 lymphocytes are potentially more cytotoxic than CD57 and CD8 cells. Taking this into consideration, the presence of the PTS in the majority of CD16 cells suggests an important role for PTS in target cell lysis.