Fc receptors for IgG, IgM, IgE and the cell surface immunoglobulins (SIg) were analysed on lymphocytes from seventeen patients with chronic lymphatic leukaemia (CLL), one with lymphosarcoma cell leukaemia (LSL), two each with hairy cell leukaemia (HCL), acute lymphatic leukaemia (ALL) and Sezary syndrome. Fc receptors for IgG and IgM were detected by rosette formation with ox erythrocytes (E(O)) sensitized with rabbit IgG (E(O)A(G)) and IgM (E(O)A(M)) anti-E(O) antibodies, respectively. Fc receptors for IgE were analysed either with E(O) coated with glutaraldehyde coupled complexes consisting of rabbit Fab' fragments of anti-E(O) antibodies and Fc fragments of an IgE myeloma protein (E(O)A(E)), or with aldehyde fixed E(O) to which IgE was absorbed. SIg of classes IgM, IgD, IgG and κ and λ light chain were detected with E(O) coated with complexes consisting of Fab'-anti-E(O) and purified F(ab')2 fragments of specific goat antibodies. Lymphocytes of all patients with CLL, LSL and HCL had Fc receptors for IgG (65 ± 15% E(O)A(G)+, normal 22.0 ± 5.8%). Ten patients had significant numbers of cells with IgM Fc receptors (37 ± 22% E(O)A(M)+, normal 1.2 ± 1.5%) which were detected without overnight culturing of the lymphocytes. Lymphocytes of four patients (two CLL, one LSL, one HCL) had Fc receptors for IgE (22 - 88% E(O)A(E)+, normal 1.8 ± 0.7%). The cells of three of these four patients were also E(O)A(M)+. The high numbers of rosetting cells indicated that individual lymphocytes must have carried more than one class of Fc receptors. The lymphocytes of the ALL and Sezary syndrome patients had few Fc receptor positive cells. Of the seventeen patients with CLL, twelve were SIgM+ and/or SIgD+, only four κ+ or λ+ and one had no SIg. The cells of the LSL and one of the HCL patients were SIgM+ and SIgD+, whilst the cells of the other HCL patient were SIgG, λ+. None of the other patients had more than 10% SIgG+ cells. The ALL and Sezary syndrome patients had low numbers of SIg+ and Fc receptor positive cells. These data indicate that lymphocytes of patients with B-cell leukaemias can carry different classes of Fc receptors simultaneously; the different classes are found in a decreasing frequency of IgG > IgM > IgE.
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