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

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.