The human cathelicidin, LL-37, induces granzyme-mediated apoptosis in cytotoxic T lymphocytes.
LL-37 is a human cationic host defense peptide (antimicrobial peptide) belonging to the cathelicidin family of peptides. In this study, LL-37 was shown to kill stimulated CD8(+) T cells (Cytotoxic T lymphocytes; CTLs) via apoptosis, while having no cytotoxic effect on non-stimulated CD8(+) or CD4(+) T cells or stimulated CD4(+) T cells. Of interest, the CD8(+) cells were much more sensitive to LL-37 than many other cell types. LL-37 exposure resulted in DNA fragmentation, chromatin condensation, and the release of both granzyme A and granzyme B from intracellular granules. The importance of granzyme family members in the apoptosis of CTLs following LL-37 treatment was analyzed by using C57BL/6 lymphocytes obtained from mice that were homozygous for null mutations in the granzyme B gene, the granzyme A gene, or both granzymes A and B. Granzymes A and B were both shown to play an important role in LL-37-induced apoptosis of CTLs. Further analysis revealed that apoptosis occurred primarily through granzyme A-mediated caspase-independent apoptosis. However, caspase-dependent cell death was also observed. This suggests that LL-37 induces apoptosis in CTLs via multiple different mechanisms, initiated by the LL-37-induced leakage of granzymes from cytolytic granules. Our results imply the existence of a novel mechanism of crosstalk between the inflammatory and adaptive immune systems. Cells such as neutrophils, at the site of a tumor for example, could influence the effector, activity of CTL through the secretion of LL-37.
Department of Biochemistry, School of Molecular and Systems Medicine, Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7. jmader@ualberta.ca
Jamie S
JS
Mader
Marcelo
M
Marcet-Palacios
Robert E W
RE
Hancock
R Chris
RC
Bleackley
D056704:Adaptive Immunity; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053804:Granzymes / Q000502:physiology*; D007249:Inflammation; D051379:Mice; D008810:Mice, Inbred C57BL; D020239:Receptor Cross-Talk; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects*; D054804:Cathelicidins
D023181:Antimicrobial Cationic Peptides; D053804:Granzymes; D054804:Cathelicidins