Pseudo-high-affinity IL-2 receptor and growth signal transduction in lymphocytes

We examined whether the pseudo-high-affinity IL-2 receptor (IL-2R) could transduce a growth signal in lymphocytes. Since lymphocytes devoid of the I chain were not available, we employed functional depletion of the I chain from a mouse T cell line CTLL-2 transfected with cDNA for the human H chain and its defective mutants which can bind IL-2 but cannot transduce a growth signal. The numbers of human H, mouse I, and mouse H chains expressed in these transfectants were similar to each other. When the human H chain (and mutants) -expressing CTLL-2 transfectants were incubated with 300 pM human IL-2, the majority of human H and mouse I chains together with the L chain formed the high-affinity receptor complex whereas the majority of mouse H chains remained free. When the human H chain mutant-expressing CTLL-2 transfectants were incubated with 300 pM human IL-2, the I chain was expected to be functionally depleted by the formation of the inactive high-affinity complex with the inactive human H chain mutants. However, the human H chain mutant-expressing CTLL-2 transfectants proliferated with a half maximal response to human IL-2 at 300-500 pM which agrees with the pseudo-high affinity Kd value displayed by the mouse L and H chains. The human H chain-expressing transfectants proliferated in response the human IL-2 in a similar kinetics with CTLL-2. CTLL-2 and the human H chain/mutants-transfectants all responded to mouse IL-2 in the same kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)