Figure 16.  IL2 downregulates IL2Ra chains on NK cells

Incubation conditions

A. Immature NK cells grown in IL15

B. Immature NK cells grown in IL2

0hr, Medium

3hr, Medium

3hr, 20nM IL2

3hr, 200pM IL2

3hr, 20nM IL15

3hr, 20nM IL15

+ 20nM IL2

In order to understand why NK cells grown in IL15 but not IL2 expressed detectable levels of surface IL2Ra chains

E14 progenitor cells were grown for 3 days in IL4 + PMA, then washed and grown for 4 days in 20nM IL15 or IL2.

They were then washed and incubated at 37o for 3 hours under the conditions shown on the left before staining

with medium [black] or biotin-anti-IL2Ra [blue] followed by AF647 streptavidin.

Conclusions

1.  Immature NK cells grown in IL15 [left hand diagrams] expressed detectable levels of IL2Ra chains.

2.  When such cells were washed and incubated in IL2 for 3 hours at 37o there was a substantial reduction in the

proportion of cells expressing high levels of IL2Ra.

3.  No such change in IL2Ra expression occurred when cells were incubated in IL15.

4.  When cells were incubated in medium alone there was also no loss of IL2Ra expression demonstrating that IL15 is not

required for the maintenance of IL2Ra expression.

5.  By contrast when cells were incubated in medium containing IL15 and IL2, IL2Ra expression was reduced to levels similar

to those found with IL2 alone.

6.  This strongly suggests that the reason that cells grown in IL15 but not IL2 have detectable surface IL2Ra expression is

because IL2 downregulates expression of IL2Ra chains.

7.  This hypothesis is supported by the finding that NK cells grown in IL2 [right hand diagrams] show augmented IL2Ra

expression not only when transferred to IL15 but when transferred to medium alone.

8.  The speed with which cells acquire surface IL2Ra chains when removed from IL2 supports the view that IL2Ra expression

in NK cells is regulated at the post-transcriptional level by treadmill ligand-induced endocytosis.

9.  Surprisingly, 200pM IL2 is as efficient as 20nM IL2 in downregulating the expression of IL2Ra chains, suggesting that most

IL2Ra chains expressed on NK cells are present in high affinity receptor complexes.