Hairy cell leukaemia occurring with an unrelated paraproteinaemia. A biochemical and immuno-electron microscopic study.

A detailed study is described of a case of hairy cell leukaemia, presenting with a serum paraprotein of an immunoglobulin (Ig) class different from that synthesised by the neoplastic cells. The case was unusual in its association with leukaemic arthropathy but ultrastructurally the hairy cells were typical. By immunofluorenscence and immuno-electron microscopy the neoplastic cells expressed IgA lambda both on the cell surface and intracellularly in the rough endoplasmic reticulum, perinuclear space and Golgi apparatus. No Ig was observed in the ribosomal-lamellae complexes. These cells also synthesised and secreted Ig of class A lambda in culture. However the serum paraprotein was of class IgA chi and could not be attributed to an abnormal population of plasma cells in the bone marrow. There was no other evidence for myeloma and the IgA chi paraproteinaemia appeared to be benign, apparently unrelated to the neoplastic proliferation of hairy cells.