Hairy-cell leukaemia: a B-lymphocytic disorder.

Fifteen cases of histologically proven hairy-cell leukaemia (HCL) were studied with immunofluorescence, rosette, and phagocytosis techniques. Unfixed hairy cells (HC) bound all kinds of labelled antiserum; but after fixation with formaldehyde a much more selective binding was observed. In two cases no surface-bound Ig was detected; four cases showed gamma and in nine cases two or three heavy chains were found, alpha and delta being the most frequent. Few cases were clearly positive for mu. The picture was invariably monoclonal with respect to light chains. Cytoplasmic Ig was present in only 3/15 cases; it was always IgM. HC did not form E-rosettes or react with a fluorescent anti-T cell antiserum. No EAIgMC-rosettes were formed. All cases showed Fc receptors, which were detected with EAIgG-rosettes (13/13) or with antigen-antibody complexes (6/6). The density of Fc receptors varied widely. Incubation with latex particles resulted in cell-associated particles in 16-63% of the HC; with Staphylococcus epidermidis, the percentage was 2-36. After enzyme treatment (lysostaphin), however, no ingested bacteria were found, which suggests that HC are essentially non-phagocytic. At least 13 cases were therefore classified as B-cell malignancies.