Normal counterparts of hairy cells and B-prolymphocytes in the peripheral blood. An ultrastructural study with monoclonal antibodies and the immunogold method.

The morphological and membrane phenotypic characteristics of normal peripheral blood B-lymphocytes were studied at ultrastructural level by means of the immunogold method with the following McAb: anti-HLA-Dr (OKIa and FMC4), FMC7, OKT10, and alpha HC1 and alpha HC2, reactive with HCL cells. Five morphological subsets of B-lymphocytes were identified: (i) 40% had a high nuclear cytoplasmic ratio, well condensed chromatin and small pale granules localised in one area of the cytoplasm, these cells expressed HLA-Dr and did not react with any of the other McAb; (ii) 40% had a prominent nucleolus, variable amount of chromatin condensation and localised granules, these cells were HLA-Dr positive and some of them expressed FMC7 as do the cells of B-PLL; (iii) 10% had a villous outline and variable numbers of polyribosomes scattered throughout the cytoplasm, some of these cells resembled morphologically HCL cells and were HLA-Dr +, FMC7 +, alpha HC1 +, alpha HC2 + and OKT10 +/-. The remaining two types of B-cells (10%) had the morphology of antibody secreting cells with parallel arrays of endoplasmic reticulum and some displayed electron dense granules in the Golgi zone. These cells were: (iv) lymphoplasmacytoid, the more common type, which were HLA-Dr +/-, FMC7-, alpha HC1-, alpha HC2 + and OKT10 +/-, and (v) plasma cells which were positive only with OKT10. The similarities in morphology and membrane markers between two of the subsets defined in this study and the cells of B-PLL and HCL suggest that they may represent normal counterparts of these B-cell malignancies.