Differences in the interleukin‐2 (IL‐2) receptor system in human and mouse: α chain is required for formation of the functional mouse IL‐2 receptor

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Abstract
Reconstitution with mouse interleukin‐2 (IL‐2) receptor subunits demonstrated that the mouse IL‐2 receptor complex was different from the human complex in the α chain requirement for the functional mouse receptor complex. The heterotrimeric complex of the mouse exogenous α and β chains and the endogenous γ chain on mouse lymphoid BW5147 cells showed the ability to bind IL‐2 with high affinity, resulting in IL‐2‐induced tyrosine phosphorylation of a cytosolic tyrosine kinase, JAK3, which is involved in IL‐2‐dependent signals. Exogenous introduction of the β chain with the endogenous γ chain, however, could neither confer appreciable IL‐2 binding nor IL‐2‐induced signal transduction on BW5147 cells, unlike the human βγ heterodimer. Mouse spleen CD8+ cells, not having the α chain initially, showed IL‐2‐dependent cell proliferation only when expression of the α chain was induced. Collectively, these results illustrate that the functional mouse IL‐2 receptor complex necessarily includes the α chain, and that the regulation of CD8+ T cell growth during immune reaction depends upon α chain expression.