Evaluation of Surface Markers on Normal Human Lymphocytes Containing Parallel Tubular Arrays: A Quantitative Ultrastructural Study

Abstract

Normal lymphocytes from the peripheral circulation represent a heterogenous population of cells with different surface markers and different functions. Some of these lymphocytes contain cytoplasmic inclusions called parallel tubular arrays (PTA), which can only be identified with certainty under the electron microscope. It is not known whether this ultrastructurally defined lymphocyte constitutes the major cell type of the T-lymphocyte population, B-lymphocyte population, or third population of lymphocytes (i.e., K cells, L cells, M cells, null cells), or is unrelated to any of these immunologically defined lymphocyte subpopulations. The purpose of this study was to determine if this morphologically identifiable lymphocyte constitutes the major cell type of any of these three lymphocyte subpopulations. A quantitative ultrastructural analysis of PTA-lymphocytes was performed on a lymphocyte-enriched fraction using three surface marker assays commonly used to identify the three major populations. Spontaneous rosettes formed with sheep erythrocytes (E-rosettes) were used as a marker for T lymphocytes. Sheep erythrocytes sensitized with rabbit IgM antibody and coated with mouse complement (EAC-rosettes) were used as a marker for B lymphocytes. Human group O, type R1R2 erythrocytes sensitized with Ripley anti-CD serum to identify the Fc receptors (EAhu-rosettes) were used as a marker for the third population of lymphocytes. Light microscopic examination of the preparations obtained from five healthy subjects revealed the following mean percentage of reacted lymphocytes: 79.2% E-rosettes, 8.8% EAC rosettes, and 16% EAhu-rosettes. Ultrastructural examination of 178 EAhu-rosettes from the five subjects revealed that 89% of the central rosette-forming lymphocyte cross-sections contained PTA. In one subject, 96% of the central rosette-forming lymphocyte cross-sections contained PTA. In contrast, examination of 369 E-rosettes obtained from five healthy subjects revealed that only 3.4% of the central rosette-forming lymphocyte cross-sections contained PTA, and examination of 151 EAC-rosettes from four healthy subjects revealed that only 11.5% of the central rosette-forming lymphocyte cross-sections contained PTA. It was concluded that parallel tubular arrays are a morphological marker for a population of lymphocytes bearing Fc receptors for cytophilic antibody identified by the EAhu-rosette assay and that the lymphocyte containing these inclusions constitutes the major cell type of the third population of lymphocytes. The possible inclusion of the PTA-lymphocyte within other lymphocyte populations and within the monocyte population is discussed.