The fine structure of normal lymphocyte subpopulations--a study with monoclonal antibodies and the immunogold technique.

The ultrastructural characteristics of normal lymphocyte subpopulations, identified by monoclonal antibodies and visualized by a colloidal gold labelled anti-mouse IgG were analysed. Our study demonstrates: (1) the major T lymphocyte subsets (OKT4+ and OKT8+) have distinct ultrastructural morphology. The majority of OKT4+ cells have a high nuclear/cytoplasmic ratio (N/C) and few cytoplasmic organelles whilst most OKT8+ cells have a low N/C ratio and numerous organelles, namely a well developed Golgi apparatus, lysosomal granules and parallel tubular arrays (PTA); (2) a unique subtype with irregular nuclear outline that resembles Sézary cells was seen in 5-10% of OKT4+ lymphocytes; (3) OKM1, a reagent that reacts with monocytes and granulocytes, is positive in a small lymphocyte subset which appears to be negative with the OKT reagents and is morphologically identical to OKT8+ cells; (4) 'hand-mirror' cells were only seen labelled with OKT8 and OKM1; (5) B lymphocytes labelled with FMC4 (anti-IA) could be distinguished from OKT3+ lymphocytes by having numerous profiles of endoplasmic reticulum (ER) and ribosomes; these were particularly prominent in lymphoplasmacytoid cells. Morphological similarities between normal T lymphocyte subsets and T neoplasias of the same membrane phenotype suggest that these disorders arise from specific T cell types present in normal peripheral blood or from common precursors.