A re-examination of the alleged monocytic features of hairy-cell leukaemia.

A number of the 'monocytic' features of the hairy cells (HCs) of hairy-cell leukemia (HCL) are studied in detail and discussed in relation to the now established B-cell nature of the disease. By means of a rosette assay employing erythrocytes coated with IgG (EAG), a receptor for the Fc of IgG is shown to be strongly expressed on all HCs, whether in suspension or in monolayers. This receptor is shed and re-expressed over a period of some 6 h. In EAG rosette formation the indicator erythrocytes are deformed and the receptor is not blocked by an antiserum to the Ia-like antigen. By ultrastructural acid-phosphatase cytochemistry, it is established that HCs phagocytose latex particles, but do not phagocytose a variety of other particles to a significant extent. These, and other features, are discussed in relation to the literature and it is shown that all are compatible with the current view that HCL is a form of B-cell lympholiferative.