The expression and function of IL-2R chains expressed on B-cell chroni
c lymphocytic leukemia (B-CLL) cells were analyzed. lL-2R alpha was ex
pressed in 31 out of 34 studied cases; in 17 cases more than 50% of th
e cells were positive whereas in three cases the proportion of IL-2R a
lpha(+) cells was less than 10%. In two patients, 6 and 13% of the cel
ls were IL-2R beta(+), in six other cases only 2-3% of the B-CLL cells
could be stained with the TU27 moAb whereas in all other cases no pos
itive cells could be detected. Equilibrium binding experiments using I
-125-rIL2 revealed high (seven out of 15 studied cases), intermediate
(four out of 15 cases) and low (five out of 15 cases) affinity IL-2R.
The number of high and intermediate affinity IL-2R was low (range: 145
-800 and 40-2800 binding sites/cells, respectively). In all cases inve
stigated, both IL-2R alpha and IL-2R beta chain mRNA could be detected
, although their quantity was variable from patient to patient. Exogen
ous recombinant IL-2 induced, in a dose-response manner, cell prolifer
ation in ten out of 23 cases and this effect was independent of the ex
pression of IL-2R alpha; however, only cells expressing high affinity
IL-2R could respond to exogenous rIL-2. Moreover, anti-IL-2R alpha moA
b could inhibit both spontaneous (in three out of five cases) and IL-2
-induced (in five out of five cases) B-CLL cell proliferation. These f
indings demonstrate that in a subgroup of B-CLL, leukemic cells are de
pendent on the IL-2/IL-2R system whereas in another group, although ce
lls expressed functional IL-2 binding sites, they could not respond to
the mitogenic signal of IL-2.