The human antimicrobial and chemotactic peptides LL-37 and a-defensins are expressed by specific lymphocyte and monocyte populations

We identified antibacterial components in human T and natural killer (NK) cells by using freshly isolated lymphocytes enriched for T and NK cells as starting material. After growing these lymphocytes for 5 days in the presence of interleukin (IL)–2, we isolated and characterized several antibacterial peptides/ proteins from the supernatant—a-defensins (HNP 1-3), LL-37, lysozyme, and a fragment of histone H2B—although other active components were also present. We then used reverse transcriptase–polymerase chain reaction to search for expression of the gene coding for LL-37 in several B-cell lines, gd T-cell lines, NK clones, and one monocytic cell line, with positive results, but found no expression in several ab T-cell lines. The a-defensins (HNP 1-3) were also found to be expressed in several of these cell lines. To confirm the presence of these antibacterial peptides in lymphocytes, we localized them to NK, gd T cells, B cells, and monocytes/macrophages by using double-staining immunohistochemical analysis of freshly isolated lymphocytes. We also found that primary cultures of lymphocytes transcribe and secrete LL-37 and that these processes are affected by IL-6 and interferon-g. In addition, we demonstrated that LL-37 has chemotactic activity for polymorphonuclear leukocytes and CD4 T lymphocytes, whereas others have shown chemotactic activity for human a-defensins (HNP 1-2). These findings suggest that microbicidal peptides are effector molecules of lymphocytes and that antibacterial activity previously shown to be derived from T and NK cells may be partly mediated by the antibacterial peptides LL-37 and HNP 1-3. (Blood. 2000;96:3086-3093)