Human natural killer cells and mature T lymphocytes express identical CD3ζ subunits as defined by cDNA cloning and sequence analysis

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Abstract
In order to characterize the CD3 ζ‐related protein found in human natural killer (NK) cells and compare it with CD3 ζ expressed in T lymphocytes, the present study was performed. A polyclonal CD3−CD16+NK population displaying a strong non‐major histocompatibility complex‐restricted cytotoxic activity against the NK target K‐562 was isolated and a product corresponding to CD3 ζ amplified using the polymerase chain reaction method. This 0.6‐kb product was present in similar amounts in NK cells and T cells. In contrast, a product corresponding to CD3 ζ was amplified from T lymphocytes exclusively. Thus, the CD3 ζ product detected in NK cells did not originate from contaminating T cells. DNA sequence analysis of two independent polymerase chain reaction products from the NK cells demonstrates that human NK cells and mature T cells share a CD3 ζ subunit with an identical primary amino acid sequence. The nucleotide sequence of a third NK‐derived cDNA revealed an insertion of a CAG triplet encoding an additional glutamine residue in the cytoplasmic domain. Since this residue is encoded by nucleotides at a putative RNA splice junction, it possibly results from a difference in pre‐mRNA splicing. Taken together, these data show that CD3 ζ is not structurally distinct in NK cells and in T lymphocytes.