The Human Antibacterial Cathelicidin, hCAP-18, Is Synthesized in Myelocytes and Metamyelocytes and Localized to Specific Granules in Neutrophils

Abstract

hCAP-18 is the only human member of the antibacterial and endotoxin-binding family of proteins known as cathelicidins. The antibacterial and endotoxin binding domains reside in the C-terminal 37 amino acids of the protein (LL-37) and this is believed to be unleashed from the neutralizing N-terminus by proteases from peroxidase positive granules. In human neutrophils, peroxidase positive and peroxidase negative granules can be subdivided into granule subsets that differ in protein content and ability to be exocytosed. To determine the localization of hCAP-18, we performed high-resolution immuno-electron microscopy and subcellular fractionation on Percoll density gradients. Biosynthesis of hCAP-18 was investigated in isolated human bone marrow cells. hCAP-18 was found to colocalize and comobilize with lactoferrin, but not with gelatinase in subcellular fractions. This was confirmed by electron microscopy. hCAP-18 is synthesized at the same stage of myeloid cell maturation as lactoferrin, and is efficiently targeted to granules. Like the peroxidase negative granule's matrix metalloproteinases, collagenase and gelatinase, hCAP-18 is also stored in unprocessed form. hCAP-18 is a major protein of specific granules where it is present in equimolar ratio with lactoferrin.

Exercise, Immunity, and Illness

“…Increased levels of AMPS (e.g., α defensins) have been observed in other body fluids (e.g., plasma) following a circulating neutrophila (Shiomi et al, 1993). The variation in the responses of different AMPs to prolonged exercise (Davison et al, 2009;Davison and Diment, 2010), therefore, may be due to the changes in the maturity of circulating neutrophils (as expressions of AMPs can vary throughout the maturation of the neutrophil in the bone marrow) or decreases in some AMPs may merely reflect neutrophils undergoing a refractory period post exercise (Cowland et al, 1995;Borregard and Cowland, 1997;Gullberg et al, 1997;Nagaoka et al, 1997;Sorensen et al, 1997;Nagaoka et al, 1998Nagaoka et al, , 2000Peake, 2002).…”

Human Antimicrobial Peptides in Bodily Fluids: Current Knowledge and Therapeutic Perspectives in the Postantibiotic Era

“…For instance, Paneth cells in the small intestine release AMPs-rich granules upon stimulation by cholinergic or bacterial stimuli, 228 and granulocytes are known to contain AMPs in granules destined for extracellular secretion. 229,230 Therefore, as the synthesis and secretion of large AMPs may not be constitutive but amenable to induction by microbial macromolecules and inflammatory cytokine stimuli, several other large AMPs may yet to be catalogued. Hence, exploration of novel large antimicrobial human peptides is an ongoing work that may yield novel therapeutic agents.…”

Unique features of human cathelicidinLL‐37

“…In addition to expression in epithelial tissues, cathelicidin is also produced by cells of the innate immune system [65,66]: human neutrophils [66,67], natural killer (NK) cells [68], dendritic cells [69], monocytes/macrophages [70,71], lymphocytes [72], mast cells [73], mesenchymal stem cells [39], and bone marrow stroma [74]. Lowry et al showed a hierarchy of expression of hCAP18 in freshly isolated peripheral blood-derived cells with low levels in lymphocytes, intermediate levels in monocytes, and the highest levels found in neutrophils.…”