Sinonasal epithelial cells synthesize active vitamin D, augmenting host innate immune function

Area of Science:

• Immunology
• Endocrinology
• Cell Biology

Background:

• Vitamin D is crucial for bone health and calcium balance.
• Emerging evidence indicates vitamin D enhances innate immunity.
• The enzyme 1-α-hydroxylase synthesizes active vitamin D and is found in various cells, including airway epithelia.

Purpose of the Study:

• To determine if sinonasal epithelial cells (SNECs) express 1-α-hydroxylase.
• To investigate the potential for local active vitamin D production in SNECs.
• To explore how local active vitamin D influences innate immune function in the nasal cavity.

Main Methods:

• Human SNECs were cultured and treated with inactive vitamin D.
• 1-α-hydroxylase expression was quantified using real-time PCR and immunocytochemistry.
• Active vitamin D levels were measured via ELISA.
• Cathelicidin expression was assessed using real-time PCR and immunocytochemistry.

Main Results:

• SNECs inherently express 1-α-hydroxylase, enabling active vitamin D synthesis.
• Stimulation with inactive vitamin D led to an eightfold increase in cathelicidin expression in SNECs.
• These findings demonstrate SNECs' capacity for local vitamin D metabolism and immune modulation.

Conclusions:

• SNECs possess the ability to generate active vitamin D.
• This local production significantly upregulates the antimicrobial peptide cathelicidin.
• The study reveals a novel mechanism for innate immune defense in the sinonasal tract via vitamin D.