New ultrastructural observations: Parallel tubular arrays in human Tγ lymphoid cells

T_γ cells are E-rosetting cells bearing Fc receptors for IgG (E⁺, Fc_γ⁺ cells). Third population (non-T, non-B) lymphoid cells are also Fc_γ⁺ cells and contain unique inclusions called parallel tubular arrays (PTA). Although T_γ cells and third population lymphoid cells should belong to a similar population of cells, previous ultrastructural studies on purified T_γ cells have failed to reveal the presence of PTA. In this study, we have unequivocally demonstrated PTA in the majority of T_γ cells using simple rosetting techniques. A total of 76 EA_hu-rosettes and 108 EA_ox-rosettes prepared from an E⁺ enriched fraction (using sheep erythrocytes as marker particles) were directly examined by electron microscopy. PTA were found in 87% of the EA_hu-rosettes and 82% of the EA_ox-rosettes. Ammonium chloride, commonly used in other laboratories to lyse erythrocytes during the purification procedure was found to cause a marked decrease in the number of ultrastructurally distinct PTA profiles. In contrast, hypotonic lysis had no effect on cellular ultrastructure. This study showed for the first time that T_γ cells are ultrastructurally similar to other Fc_γ⁺ lymphoid cells and contain PTA as a distinct marker. The significance of our findings to the basic function of this E⁺Fc_γ⁺ lymphoid population is discussed.