Enhanced complement-susceptibility and dysfunction of lymphocytes in paroxysmal nocturnal haemoglobinuria (PNH)

We investigated the complement-susceptibility of paroxysmal nocturnal haemoglobinuria (PNH) lymphocytes in relation to their dysfunction. When assessed by complement-mediated lysis induced by monoclonal antibodies (CD5 or CD20) and rabbit complement, the complement-susceptibility of lymphocytes from patients with PNH, both CD5+ (T cells) and CD20+ (B cells), was greater than that from controls (P less than 0.001). This susceptibility was further enhanced, both in normal controls (P less than 0.01) and in patients with PNH (P less than 0.001), when the activity of decay-accelerating factor (DAF) on the lymphocytes was blocked with anti-DAF monoclonal antibody. DAF amounts in mononuclear cells (MNC) from patients with PNH, measured by an enzyme-linked immunosorbent assay (ELISA), were lower than those of the controls (P less than 0.001). The expressions of DAF on T cells and on B cells from patients with PNH were significantly decreased (P less than 0.05 in T cells: P less than 0.01 in B cells). MNC from patients with PNH responded less to phytohaemagglutinin (PHA) and concanavalin A (Con A) than MNC from the controls (P less than 0.001). In contrast, the responses of PNH MNC to poke weed mitogen (PWM) or lipopolysaccharide (LPS) were not impaired. MNC from a normal donor preincubated with anti-DAF became less responsive to PHA or Con A. We conclude that PNH lymphocytes show enhanced complement-susceptibility and that they are involved in their own expression of DAF as well as in other types of peripheral blood cells. The results of the responses to various lectins suggest the dysfunction of T cells in PNH.