Characterization of Two Morphologically Distinct Leu‐7+ Cell Subsets with Respect to Leu‐15 Antigen

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Abstract
In the present study the fine structures of Leu‐7‐Leu‐15+ and Leu‐7+‐Leu‐15 cell subpopulations were characterized by using an immunogold‐immunoperoxidase double labelling in electron microscopy. The densities of Leu‐15 antigenic sites on both E rosetting (Er) and non‐adherent/non‐E rosetting (non‐A/non‐Er) Leu‐15 positive cell surfaces were also evaluated by using an immunogold analysis in electron microscopy. A majority of Leu‐7+ cells co‐expressed I he Leu‐15 antigen and showed an ultrastructural pattern specific for mature natural killer (NK) cells, i.e. abundant cytoplasm with many organelles. numerous electron dense granules and irregular outline. On the other hand, a minority of Leu‐7‐ ceils did not express the Leu‐15 antigen and showed a clearly different ultrastructural feature in comparison to Leu‐7+‐Leu‐15+ cells T hus, the presence of the Leu‐15 antigen on Leu‐7 + cell surface corresponds to ultrastructural features specific to differentiated NK cells and may represent an expression of Leu‐7+cell differentiation. An alternative hypothesis may he that Leu‐7+‐Leu‐15‐ and l.eu‐7‐Leu 15 cells represent distinct cell lineages within non‐A/non‐Er Leu‐7+ cells. Finally, the results of the present study provide proof that Leu‐7+ antigen is more frequently represented on non‐A/non‐Er Leu‐L‐15+ cells than on Er Leu‐15+ cells.