New Version,synthetic peptides with dual antimicrobial and immunomodulatory action

Antimicrobial peptides (AMPs) are fundamental components of the innate immune system, acting as a first line of defense against invading pathogens. In humans, these peptides play a particularly significant role in the activation and function of human mast cells. These versatile immune cells, which are abundantly expressed in mast cells, are key players in both immediate and adaptive immune responses. The intricate relationship between antimicrobial peptide and mast cell biology is an area of intense research, revealing how these molecules contribute to host defense, inflammation, and tissue homeostasis.

A prominent class of antimicrobial peptides involved with mast cells are cathelicidins. The sole human cathelicidin, known as LL-37 (also referred to as human antibacterial peptide LL-37), is a well-studied example. LL-37 is not only produced by various cell types but is also expressed by mast cells themselves, creating a localized antimicrobial environment. Research indicates that LL-37 can recruit mast cells, and subsequently, these mast cells can produce LL-37 to kill bacteria. This bidirectional interaction highlights the self-amplifying nature of the innate immune response mediated by these peptides.

Beyond their direct microbicidal activity, antimicrobial peptides possess potent immunomodulatory properties. For instance, Human β-defensin3 (hBD3) and LL-37 are recognized as host defense peptides (HDPs) that not only directly eliminate microbes but also exhibit immunomodulatory/wound healing capabilities. This dual functionality is crucial for effective host defense, as it allows for the simultaneous eradication of pathogens and the orchestration of a controlled inflammatory and repair response.

The activation of human mast cells by antimicrobial peptides often involves complex signaling pathways. Several studies have demonstrated that peptides like Pleurocidin, a novel antimicrobial peptide, can induce human mast cell activation through the FPRL1 receptor. Furthermore, other antimicrobial peptides have been shown to activate mast cells via Mas-related G protein-coupled receptors (GPCRs). For example, AG-30/5C activated LAD2 human mast cells to degranulate and release lipid mediators such as leukotriene C4 and prostaglandin D2. This activation can lead to the release of histamine and other inflammatory mediators, contributing to the inflammatory cascade.

The diversity of antimicrobial peptides that can interact with human mast cells is extensive. Research has identified synthetic peptides with dual antimicrobial and immunomodulatory action that target mast cell-specific pathways. Even small-molecule host-defense peptide mimetic antibacterial and antifungal agents can activate human and mouse mast cells via Mas-related GPCRs. This broad engagement underscores the central role of mast cells as responders to a wide array of antimicrobial peptide stimuli.

Interestingly, some antimicrobial peptides have also been shown to exert anti-allergic effects. The antimicrobial peptide Pro10-1D has demonstrated efficacy in inhibiting antigen-induced degranulation of mast cells, suggesting a potential therapeutic role in allergic conditions. This finding adds another layer to the complex involvement of antimicrobial peptides in mast cell-mediated immune responses.

The presence of antimicrobial peptides is not confined to specific infection sites; they are considered important innate immune molecules at microbe–host interfaces, including the skin. Antimicrobial peptides in the skin are mainly produced by epithelia of several organs including skin, contributing to the protection of these surfaces. Their ability to kill skin pathogens and initiate potent host responses is vital for maintaining skin integrity and health.

In summary, the interaction between antimicrobial peptides and human mast cells is a critical aspect of innate immunity. From direct pathogen killing to modulating inflammatory responses and even exhibiting anti-allergic properties, these peptides are indispensable in safeguarding human health. The ongoing exploration of novel peptides and their mechanisms of action promises to further illuminate this vital microbial defense system and its implications for various physiological and pathological conditions.