Human β-defensin 2: a connection between infections and allergic skin diseases

Beta defensins (β-defensins) are peptides primarily produced by epithelial cells in mammals to safeguard the skin, other organs, and mucosa from microbial colonization. These peptides are generated by epithelial cells, keratinocytes, and macrophages, mainly in response to interactions with microorganisms (bacteria, viruses, and fungi) or the influence of various pro-inflammatory cytokines. Human β-defensin (HBD) 2 plays an indirect role in allergic reactions by promoting mast cell activation and degranulation. In dermatological and allergic conditions, the role of HBD2 has been well documented. Although HBD2 is predominantly produced in keratinocytes, along with HBD3 it has also been detected in serum. Elevated serum levels of HBD2 have been observed in patients with skin diseases such as atopic dermatitis and psoriasis. In addition, HBD2 is significant in chronic spontaneous urticaria (CSU), in which urticarial skin lesions can be triggered by infections. Notably, CSU is often accompanied by angioedema, which may be related to HBD2 because patients with CSU and associated angioedema have higher serum HBD2 levels compared to those without angioedema. Current evidence suggests that HBD2 could serve as a marker of inflammation and may have potential therapeutic applications. However, due to limited data on HBD2 levels and its expression in the skin of patients with allergic skin diseases, further research is needed to elucidate the underlying causes and mechanisms of elevated HBD2 levels in these conditions.