Primate retroelement exonization and sexually dimorphic IL13RA1 transcription tune type 2 immune responses

Type 2 immunity is orchestrated by IL-4 and IL-13 signaling, initiated by binding to receptors that are specific to each cytokine or to the shared heterodimeric receptor comprising the IL-4Rα and IL-13Rα1 subunits. Here, we report that sexually dimorphic IL13RA1 transcription is regulated by estrogen and characterize an IL-13Rα1 isoform (referred to here as IL-13Rα1-LOR1a) created through facultative splicing to an alternative terminal exon composed of primate-specific retrotransposable elements (RTEs). At the mRNA level, RTE exonization replaces regulatory sequences in the canonical 3' untranslated region (3'UTR) implicated in IL13RA1 mRNA stability. Moreover, alternative splicing removes critical domains in the cytoplasmic tail, rendering the IL-13Rα1-LOR1a isoform partially signaling defective at the protein level. When coexpressed, the IL-13Rα1-LOR1a isoform antagonizes the function of the canonical receptor, reducing cellular responsiveness to IL-4 and IL-13. Thus, the balance of the two IL13RA1 isoforms appears to fine-tune type 2 cytokine signaling and downstream immune responses.