Cytokines

Key Biological Properties: Beta defensins are typically 2 to 6 kDa in size and contain three pairs of intramolecular disulfide bonds . They are cationic and microbicidal, active against a wide range of pathogens .

Expression Patterns: Beta defensins are produced by various cell types, including epithelial cells lining organs such as the epidermis, bronchial tree, and genitourinary tract . They are also found in white blood cells like macrophages, granulocytes, and NK-cells .

Tissue Distribution: Beta defensins are widely distributed across different tissues. For instance, in cows, as many as 13 beta-defensins exist in neutrophils . In humans, they are found in epithelial cells of various organs .

Primary Biological Functions: The primary function of beta defensins is to provide antimicrobial defense by disrupting the membranes of pathogens . They also play a role in immune responses by inducing the activation and degranulation of mast cells, leading to the release of histamine and prostaglandin D2 .

Role in Immune Responses: Beta defensins are involved in the innate immune response, acting as the first line of defense against microbial invasion . They help in pathogen recognition and initiate immune responses by binding to receptors such as toll-like receptors (TLR) and nod-like receptors (NLR) .

Mechanisms with Other Molecules and Cells: Beta defensins interact with the membranes of invading microbes, which are negatively charged due to lipopolysaccharides (LPS) and lipoteichoic acid (LTA) in the cell membrane . They have a higher affinity for these binding sites compared to Ca2+ and Mg2+ ions, leading to membrane destabilization .

Binding Partners and Downstream Signaling Cascades: Beta defensins can form net-like structures that entrap bacteria, preventing their migration and invasion . This redox-dependent function serves as an additional mechanism of action, differing from other defensins .

Control of Expression and Activity: The expression of beta defensins is regulated by various pathways, including the toll-like receptors (TLRs)/nuclear factor-kappa B (NF-κB) pathway . Alternative pathways such as mitogen-activated protein kinase (MAPK) and epigenetic regulation also contribute to their regulation .

Transcriptional Regulation and Post-Translational Modifications: Beta defensins are usually translated from characteristic two-exon gene structures . The first exon encodes a pre-pro-peptide, while the mature peptide is encoded by the second exon, containing the six cysteine motif .

Biomedical Research: Beta defensins are used in research to understand their role in immune responses and their potential as antimicrobial agents .

Diagnostic Tools: They have potential applications in diagnostic tools due to their ability to recognize and bind to specific pathogens .

Therapeutic Strategies: Beta defensins are being explored as therapeutic agents for their antimicrobial properties and their ability to modulate immune responses .

From Development to Aging and Disease: Beta defensins play a role throughout the life cycle, from development to aging . They are expressed pre-birth and disruptions in their regulation may contribute to disease susceptibility . In adults, they help maintain homeostasis and protect against infections .