Facultative Phagocytosis by Leukemic B-Lymphocytes: Further Proof of the B-Cell Nature of Hairy Cells

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Almost since the first good description of hairy cell leukemia (HCL), also known as leukemic reticuloendotheliosis (LRE), was given by Bouroncle et al. [3], there have been conflicting arguments on the origin of the characteristic hairy cell. Possible candidates for the origin of hairy cells are shown in Table 1. A more detailed discussion of the subject is given elsewhere [4]. Most workers have argued the possibility that these cells are related to monocytes or B-lymphocytes. Evidence for B-lymphocyte origin has been provided primarily by the demonstration of surface-bound immunoglobulins (SIg), mainly IgM and IgD, and less frequently IgG, usually, but not always, shown to be monoclonal [4, 5, 9, 11, 12, 13, 18]. Furthermore, several groups have now demonstrated resynthesis of monoclonal immunoglob- Table 1 Candidates for the origin of hairy cells 1. Monocyte—macrophage [15] 2. B-lymphocyte [4, 5,9, 10, 12, 13, 16,18] 3. K cells [4] 4. Human equivalent to the mouse ‘dendritic’ cell [8] 5. B-lymphocyte with phagocytic properties [11, 17, 19] Open image in new window Fig.1 A peripheral blood lymphocyte from a case of chronic lymphocytic leukemia (B-cell type) showing binding of latex particles and one ingested particle. (Lead-uranyl acetate; x 15,000) Open image in new window Fig.2 A peripheral blood cell from a case of prolymphocytic leukemia (B-cell type) showing three latex particles phagocytosed. (Lead-uranyl acetate; × 13,000) Open image in new window Fig.3 A hairy cell from the spleen of a case of HCL showing phagocytosis (two particles) and surface binding (several particles) of latex. (Lead-uranyl acetate; × 11,000) Open image in new window Fig.4 A normal peripheral blood monocyte with numerous ingested latex particles. Note that several particles are contained within the same phagocytic vacuole. (Lead-uranyl acetate; x8000) ulins after the SIg have been removed by a variety of means (trypsinization, prolonged incubation at 37° in serum-free media, etc.) [10, 11, 12, 16, 17, 19]. The lymphocyte nature is also supported by the binding of mouse RBC [6] and in rare cases of sheep RBC [1]. On the other hand, other workers have emphasized the undoubted capacity of hairy cells to phagocytose latex particles and some microorganisms [8, 11, 15, 17, 19], a function primarily related to monocytes and not lymphocytes. The finding of both B-cell surface characteristics and phagocytic potential led to the suggestion that hairy cells may correspond to a hitherto unrecognized cell type: a B-lymphocyte with phagocytic properties [11, 19]. However, few workers have carried out studies on the phagocytic capacity of lymphocytes. Early reports [2, 14, 20, 21] suggested that some cells, morphologically identified as lymphocytes, may be able to phagocytose.