Hairy cell leukaemia: surface markers and functional capacities of the leukaemic cells analysed in eight patients.

In eight patients with hairy cell leukaemia (HCL) peripheral blood cells and in two patients also spleen cells were analysed for surface markers and functional capacities. Only cells containing the tartrate resistant isoenzyme 5 of the acid phosphatase were considered. Hairy cells (HC) of all patients were found to adhere spontaneously to glass and plastic surfaces and to spread after adherence like monocytes. They ingested latex particles of more than 1 micron diameter, but, in contrast to monocytes, did not phagocytose erythrocytes sensitized either by IgM or by IgG antibodies. HC of all patients bore Fc-receptors with a high binding affinity for aggregated IgG. Using 125 I-labelled F(ab')2-fragments of monospecific antibodies in autoradiography, only one light chain type was detected on HC of individual patients. In four patients mu- and delta-chains were simultaneously expressed on HC, whereas in two patients only gamma-chains and in one case only mu-chains were observed on HC. One patient showed a combination of gamma- and delta-chains on his HC. A great variation in density of surface immunoglobulings of HC was observed within individual patients. After removal by capping, surface immunoglobulin reappeared on HC during cell culture, but more slowly than on normal B-lymphocytes. As shown in two patients by internal labelling, HC secreted immunoglobulin light chains, but no heavy chains. On the basis of these findings the classification of HC as belonging to the B-cell lineage, rather than to the monocytic lineage, seems to be justified.