IL-4 down-regulates IL-2 receptor p75 by accelerating its endocytosis

: We examined the effects of interleukin 4 (IL-4) on the expression of IL-2 receptor p75 (IL-2R p75) or beta chain on various human T cells. IL-4 promptly down-regulated surface IL-2 receptor (IL-2R) p75 in these cells. Although IL-2-induced IL-2R p75 down-regulation was seen more quickly, IL-2 did not contribute to the process of the IL-4-induced decrease of IL-2R p75. Northern blotting revealed that IL-4 did not reduce the expression of IL-2R p75 mRNA. Studies using Pronase E, which digests cell surface IL-2R p75, or brefeldin A, which blocks intracytoplasmic protein transport from endoplasmic reticulum to the Golgi apparatus, suggest that IL-4-induced IL-2R p75 down-regulation is controlled after IL-2R p75 is expressed on the cell surface. We found that IL-4 accelerated the endocytosis of IL-2R p75, which was monitored by [125I]Mik-beta 3 monoclonal antibody that recognizes non-IL-2-binding epitope on IL-2R p75. These findings demonstrate that IL-4 down-regulates IL-2R p75 mainly by accelerating its endocytosis.