Na⁺/H⁺ exchange activation mediates the lipopolysaccharide-induced proliferation of human B lymphocytes and is impaired in malignant B-chronic lymphocytic leukemia lymphocytes

In various mammalian cell types the stimulation of the plasma membrane amiloride-sensitive Na⁺/H⁺ exchange and the resulting increase of intracellular pH (pH(i)) play a key role in the initiation of cell proliferation. In the present work we have investigated whether Na⁺/H⁺ exchange is involved in normal human B cell proliferation and whether it is also operating in malignant B-chronic lymphocytic leukemia (B-CLL) lymphocytes. Our results show that: 1) normal human B cells contain an operating Na⁺/H⁺ exchanger, as inferred by their ability to recover pH(i) after acid-loading in a HCO₃^--free medium and by evidences that LPS and phorbol ester PMA elicit a pH(i) rise inhibitable by either 5-(N-ethyl-N-isopropyl)amiloride (EIPA) or a Na⁺-free medium; 2) LPS-induced proliferation of normal human B cells is strongly inhibited when the amiloride analog EIPA (5 μM) is present in the culture medium (after 72 h the proportion of B cells incorporation bromodeoxyuridine falls from 13.9 ± 3.9% to 2.8 ± 1.1%); 3) EIPA does not affect BdR incorporation when B cells proliferation is induced by the co-mitogenic activity of IL-4 and low m.w. B cell growth factor (BCGF); 4) B-CLL cells, which proliferate in response to IL-4/BCGF but not to LPS, fail to increase pH(i) above their pH(i) resting levels when challenged with LPS or PMA and pH(i) recovery after acid-loading is highly impaired. These results lead to conclude that Na⁺/H⁺ exchange operation is necessary for LPS-(but not for Il-4/BCGF)-induced proliferation of human normal B lymphocytes and that Na⁺/H⁺ exchange activation is impaired in malignant B-CLL lymphocytes.