No abstract

Summary. Functional studies were performed on the ‘hairy’ cells of five cases of leukaemic reticuloendotheliosis (LRE) to see whether they behaved as histiocytes or lymphocytes. The ‘hairy’ cells were less active than normal or leukaemic monocytes in respect of adhesion to glass, transformation to macrophages and phagocytosis and killing of Candida; they also lacked IgG and C3 receptors for immune phagocytosis. Surface‐bound immunoglobulins were demonstrated in a high proportion of ‘hairy’ cells; and they did not form rosettes with sheep red cells. Similar results were obtained with the lymphocytes of chronic lymphocytic and prolymphocytic leukaemia. In addition, the majority of the ‘hairy’ cells in one case were found to have C3 receptors for immune complexes. The ‘hairy’ cells of three patients did not respond to phytohaemagglutinin (PHA) or to pokeweed mitogen (PWM) but, in another case, half the cells transformed normally with PHA. It is concluded that the ‘hairy’ cell is of lymphocytic origin (resembling B lymphocytes) and that LRE should be included within the lymphoproliferative disorders and differentiated from histiocytic‐cell disorders.

SYNOPSIS The PAS and acid phosphatase reactions showed a different pattern of positivity in the cells of lymphoproliferative disorders according to their B or T cell nature. In B-cell leukaemias (chronic lymphocytic and prolymphocytic) a low proportion of lymphocytes gave a positive result with the acid phosphatase reaction, while the majority were PAS positive in granular form. In contrast, in the T-prolymphocytic and T-lymphoblastic leukaemias the acid phosphatase reaction was positive in the majority of cells, while the PAS reaction was only positive in a minority. The significance of these findings, particularly for the recognition of a distinct T-cell variant of acute lymphoblastic leukaemia, is discussed.