Beta-defensin 3 and Cathelicidin-mediated Chemokine Induction in Monocytes and Macrophages

Background: Chemokines attract various cell types to tissues and are important for modulating inflammation and immune responses. Antimicrobial peptides are produced at epithelial barriers.  These molecules have chemotactic properties and can activate antigen-presenting cells such as monocytes, thereby, contributing to both innate and adaptive immune responses. 

Objectives: To investigate the ability of antimicrobial peptides-i.e., human beta defensin-3 (hBD-3) and cathelicidin (LL-37), to modulate co-stimulatory molecule expression and chemokine production by monocytes and macrophages in vitro.

Methods: Peripheral blood was obtained from 6 healthy adult volunteers. Monocytes were purified to achieve >85% purity. Cells were incubated overnight in medium alone, in medium plus hBD-3 (20ug/ml), LL-37 (20ug/ml) or PAM3CSK4 (500ng/ml) as a positive control. Culture supernatants were frozen at -20^oC until assessed by infrared array technology for various chemokines, cytokines and angiogenic factors. Cells recovered at the end of the culture period were examined by flow cytometry for expression of co-stimulatory molecules, CD80 and CD86.   Monocytes from 4 subjects were cultured for 7 d with M-CSF (100 ng/ml) to induce maturation into macrophages.  Cells were stimulated as above and assessed for cell phenotype and chemokine production.

Results: HBD-3 induced surface expression of both CD80 and CD86 on monocytes, whereas LL-37 only induced CD86 expression on monocytes. hBD-3 induced a variety of chemokines in monocytes including monocyte-derived chemokine, monocyte-chemotactic protein-1 and  macrophage inflammatory protein-β as well as angiogenesis factors, GROα and vascular-endothelial growth factor (p values <0.05). LL-37 also induced chemokines, but generally at lower levels than hBD-3.  Similar results were obtained with monocyte-derived macrophages.   

Conclusion: By modulating chemokine production in monocyte/macrophages, hBD-3 and LL-37 can influence the cellular and inflammatory milieu at sites of microbial challenge.  These data support a role for antimicrobial peptides in immune regulation and tissue repair.