Novel antiviral activity of chemokines.

Antimicrobial peptides are a diverse family of small, mostly cationic polypeptides that kill bacteria, fungi and even some enveloped viruses, while chemokines are a group of mostly cationic small proteins that induce directed migration of leukocytes through interactions with a group of seven transmembrane G protein-coupled receptors. Recent studies have shown that antimicrobial peptides and chemokines have substantially overlapping functions. Thus, while some antimicrobial peptides are chemotactic for leukocytes, some chemokines can kill a wide range of bacteria and fungi. Here, we examined a possible direct antiviral activity of chemokines against an enveloped virus HSV-1. Among 22 human chemokines examined, chemokines such as MIP-1 alpha/CCL3, MIP-1 beta/CCL4 and RANTES/CCL5 showed a significant direct antiviral activity against HSV-1. It is intriguing that these chemokines are mostly known to be highly expressed by effector CD8+ T cells. The chemokines with a significant anti-HSV-1 activity commonly bound to HSV-1 virions via envelope glycoprotein gB. Electron microscopy revealed that the chemokines with a significant anti-HSV-1 activity were commonly capable of generating pores in the envelope of HSV-1. Thus, some chemokines have a significant direct antiviral activity against HSV-1 in vitro and may have a potential role in host defense against HSV-1 as a direct antiviral agent.

CCL28 has dual roles in mucosal immunity as a chemokine with broad-spectrum antimicrobial activity.

CCL28 is a CC chemokine signaling via CCR10 and CCR3 that is selectively expressed in certain mucosal tissues such as exocrine glands, trachea, and colon. Notably, these tissues commonly secrete low-salt fluids. RT-PCR analysis demonstrated that salivary glands expressed CCL28 mRNA at the highest levels among various mouse tissues. Single cells prepared from mouse parotid glands indeed contained a major fraction of CD3(-)B220(low) cells that expressed CCR10 at high levels and CCR3 at low levels and responded to CCL28 in chemotaxis assays. Morphologically, these cells are typical plasma cells. By immunohistochemistry, acinar epithelial cells in human and mouse salivary glands were strongly positive for CCL28. Furthermore, human saliva and milk were found to contain CCL28 at high concentrations. Moreover, the C terminus of human CCL28 has a significant sequence similarity to histatin-5, a histidine-rich candidacidal peptide in human saliva. Subsequently, we demonstrated that human and mouse CCL28 had a potent antimicrobial activity against Candida albicans, Gram-negative bacteria, and Gram-positive bacteria. The C-terminal 28-aa peptide of human CCL28 also displayed a selective candidacidal activity. In contrast, CCL27, which is most similar to CCL28 and shares CCR10, showed no such potent antimicrobial activity. Like most other antimicrobial peptides, CCL28 exerted its antimicrobial activity in low-salt conditions and rapidly induced membrane permeability in target microbes. Collectively, CCL28 may play dual roles in mucosal immunity as a chemoattractant for cells expressing CCR10 and/or CCR3 such as plasma cells and also as a broad-spectrum antimicrobial protein secreted into low-salt body fluids.