Human CD3−CD16+ natural killer cells express the hGATA‐3 T cell transcription factor and an unrearranged 2.3‐kb TcR δ transcript

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Abstract
In this study we analyzed the Tcell receptor(TcR) δ transcripts expressed by CD3−CD16+ cells and we investigated whether these cells expressed the hGATA‐3 Tcell transcription factor and the recombination‐activating gene (RAG)‐l.Multiple TcR δ transcripts deriving from an unrearranged TcR δ gene were detected in both polyclonal and clonal CD3−CD16+ natural killer(NK) cell lines. Two unrearranged TcR δ transcripts had a size similar to that of the functional TcR δ mRNA (2.3 and 1.3 kb) found in TcR γ/δ+ T lymphocytes. Sequence analysis of nine different 2.3‐kb cDNA clones obtained from NK‐derived polyA+ RNA confirmed that they corresponded to an unrearranged TcR δ gene. These cDNA were 2343 bp long and their transcription initiation site was located 814 bp upstream from the Jδ1 segment. The sequence located upstream of the Jδ1 segment corresponded to the previously reported germ‐line sequence. The Jδ1 segment was correctly spliced to Cδ; in addition the four Cδ exons were found to be already assembled. Two polyadenylation sites were present in the fourth Cδ exon. However, only that located at the 3′ end appeared to be utilized in the 2.3‐kb cDNA. The expression of hGATA‐3, a T cell‐specific factor known to be involved in the regulation of the transcription of TcR δ locus, was analyzed by Northern blot, in cultured NK cell population and clones (but not in freshly derived cell populations). All NK clones and cell lines studied were found to express hGATA‐3‐specific mRNA, suggesting that hGATA‐3 may be involved in the regulation of the unrearranged TcR δ gene expression in NK cells. Finally, no transcription of the RAG‐1 gene could be detected in all NK cell lines or clones analyzed.