Most cases of hairy-cell leukaemia (HCL) involve proliferations of neoplastic B lymphocytes. In rare cases, M-proteins or osteolytic lesions have been documented in patients with HCL. In this study two patients with typical HCL are reported in whom both paraproteinaemia and osteolytic lesions of the femoral neck developed. In one of the patients the production of the M-protein by hairy cells could be established. In the other patient, at autopsy no signs of myeloma were found. The hairy cells from inside the osteolytic lesion had the same immunological phenotype as hairy cells from the peripheral blood, the spleen, and other parts of the bone marrow. These cases once more confirm the B-cell nature of many cases of HCL, and show that hairy cells can have functional capacities usually attributed to much more mature B lymphocytes, i.e. plasma cells.

5 sera from a series of more than 1,000 serum samples from hospitalized patients tested by immunoelectrophoresis were selected for further examination because of a disproportional increase in the anodic part of IgG. A marked polyclonal increase in IgG4 subclass level was detected in each of these sera. While the patients suffered from a variety of diseases (e.g. Loeffler’s syndrome, leiomyosarcoma, periarteritis nodosa, chronic bronchitis, and mycosis fungoides, respectively), they all had an acquired respiratory disease as the only common clinical denominator.

A 64‐year‐old woman who has suffered from chronic lymphocytic leukaemia since 1976 is discussed. In 1978, an abnormal protein component was found in her serum by means of immunoelectrophoresis. Using the techniques of immunoselection of the serum immuno‐globulins and immunofluorescence of the bone marrow cells, it was demonstrated that this component consists of IgG1 heavy chains only. The native protein, COL, consisted of a dimer linked by disulphide bonds of a molecular weight of 80000 daltons. Its monomeric unit had a molecular weight of 40000 daltons, as determined by SDS‐polyacrylamide gel electrophoresis after reduction with 2‐mercaptoethanol. Protein COL was not produced by the leukaemic cells (which bore IgM‐γ on their membrane) but by a morphologically distinct clone of lymphoid cells. After therapy with chlorambucil, the level of the heavy chain disease protein in the serum decreased substantially.

Summary. Most cases of hairy‐cell leukaemia (HCL) involve proliferations of neoplastic B lymphocytes. In rare cases, M‐proteins or osteolytic lesions have been documented in patients with HCL. In this study two patients with typical HCL are reported in whom both paraproteinaemia and osteolytic lesions of the femoral neck developed. In one of the patients the production of the M‐protein by hairy cells could be established. In the other patient, at autopsy no signs of myeloma were found. The hairy cells from inside the osteolytic lesion had the same immunological phenotype as hairy cells from the peripheral blood, the spleen, and other parts of the bone marrow. These cases once more confirm the B‐cell nature of many cases of HCL, and show that hairy cells can have functional capacities usually attributed to much more mature B lymphocytes, i.e. plasma cells.

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