Morphological heterogeneity of Leu7, Leu11 and OKM1 positive lymphocyte subsets: an ultrastructural study with the immunogold method.

The morphological features of normal peripheral blood lymphocytes reactive with three monoclonal antibodies (MoAb) against natural killer (NK) cells, Leu7, OKM1 (CD11b) and Leu11 (CD16) and with two anti-T cell MoAb, CD4 and CD8, have been analysed at ultrastructural level by an indirect immunogold method. Cells having the features of large granular lymphocytes (LGL) but also lymphocytes displaying different morphological characteristics (non LGL; e.g. high nucleo-cytoplasmic ratio and few cytoplasmic organelles) were seen reactive with each of the MoAb investigated. Leu7 identified a higher proportion of LGL (60-80%) than OKM1 (10-95%) and Leu11 (20-48%), and with a stronger binding. A distinct granular structure, recognized as parallel tubular arrays, was more characteristic of the Leu7+, CD8+ LGL and was less frequently seen in the OKM1 and Leu11 positive LGL subpopulation in four out of the five donors investigated. It is of interest that the Leu11 and OKM1 positive subsets, which correspond functionally to cells with greater NK function, had relatively less LGL than the Leu7 positive subsets, raising the issue of the true morphology of NK cells in man. The existence of a minority of CD4 positive LGL was confirmed. Our findings demonstrate that there is a degree of morphological heterogeneity within the normal NK lymphoid population as defined by the membrane phenotype and that certain variability among normal individuals regarding the proportion and structural features of the NK subpopulations may be present.