Suppression of mitogen- and antigen-induced lymphocyte proliferation by lanthanides.

Lanthanide ions (Ln3+) inhibited the proliferative response of human lymphocytes to various polyclonal mitogens and the 'purified protein derivative' (PPD) of the tuberculin antigen. Of the four Ln3+ ions tested lanthanum (La3+) was the strongest inhibitor; erbium (Er3+) and lutetium (Lu3+) were only weakly active, while samarium (Sm3+) had intermediate potency. At a concentration of 1 mM, La3+ almost completely inhibited the uptake of [3H]-thymidine by lymphocytes exposed to mitogenic agents. Trypan blue exclusion tests confirmed that the La3+ ions were not toxic. These findings may bear upon the reported anti-inflammatory properties of the lanthanides.