T cell receptor complexes containing FcεRIγ homodimers in lieu of CD3ζ and CD3η components: A novel isoform expressed on large granular lymphocytes

CD3ζ and CD3η form disulfide-linked homo- or heterodimers important in targeting partially assembled Tiα-β/CD3γδε T cell receptor (TCR) complexes to the cell surface and transducing stimulatory signals after antigen recognition. Here we identify a new TCR isoform expressed on splenic CD2⁺, CD3/Tiα-β⁺, CD4^-, CD8^-, CD16⁺, NK1.1⁺ mouse large granular lymphocytes (LGL), which are devoid of CD3ζ and CD3η proteins. The TCRs of this subset contain homodimers of the γ subunit of the high affinity receptor for IgE (FcεRIγ) in lieu of CD3ζ and/or CD3η proteins. The LGL display natural killer-like activity and are cytotoxic for B cell hybridomas producing anti-CD3ε and anti-CD16 monoclonal antibodies, demonstrating the signaling capacity of both TCR and CD16 in this cell type. These findings provide evidence for an additional level of complexity of TCR signal transduction isoforms in naturally occurring T cell subsets.