NK-lysin, a novel effector peptide of cytotoxic T and NK cells. Structure and cDNA cloning of the porcine form, induction by interleukin 2, antibacterial and antitumour activity.

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Abstract
A 78 residue antimicrobial, basic peptide, NK‐lysin, with three intrachain disulfide bonds was purified from pig small intestine and characterized. A corresponding clone was isolated from a porcine bone marrow cDNA library. The 780 bp DNA sequence had a reading frame of 129 amino acids which corresponded to NK‐lysin. The clone was used to show that stimulation with human interleukin‐2 induced synthesis of NK‐lysin‐specific mRNA in a lymphocyte fraction enriched for T and NK cells. Lower levels of mRNA were detected in tissues known to contain T and NK cells, such as small intestine, spleen and colon. Interleukin‐2 also induced both proliferation of the lymphocyte fraction and cytolytic function in these cells. Immunostaining showed that NK‐lysin was present in cells positive for CD8, CD2 and CD4. NK‐lysin showed high anti‐bacterial activity against Escherichia coli and Bacillus megaterium and moderate activity against Acinetobacter calcoaceticus and Streptococcus pyogenes. The peptide showed a marked lytic activity against an NK‐sensitive mouse tumour cell line, YAC‐1, but it did not lyse red blood cells. The amino acid sequence of NK‐lysin exhibits 33% identity with a putative human preproprotein, NKG5, of unknown function but derived from a cDNA clone of activated NK cells. We suggest that NK‐lysin is a new effector molecule of cytotoxic T and NK cells.