Structural and functional characteristics of hairy cells.

Morphological, cytochemical, immunological and ultrastructural studies were performed on peripheral blood mononuclear cells from a patient with hairy-cell leukemia. Immunofluorescence studies showed a very strong intensity of fluorescence and indicated that hairy cells had monoclonal surface-membrane immunoglobulins (SmIg) actively produced by the cells. An unusual spontaneous SmIg redistribution induced by antibodies was also noted. Immunoultrastructural studies demonstrated that antibody-induced redistribution of SmIg on hairy cells is in form of a singular polar cap and that the cell membrane is rapidly cleaned of the complexes by endocytosis. The behavior of hairy cells regarding several membrane markers, mitogen stimulation and antibody-induced cytotoxicity suggests that hairy projections could represent the expression of a functional stage common to different lymphocyte subpopulations, or alternatively, a marker of a peculiar subset of B lymphocytes.