Mariola Marchlewicz, Paulina Sagan, Marta Grabowska, Magdalena Kiedrowicz, Magdalena Boer, Joanna Kruk, Małgorzata Piasecka, Ewa Duchnik
Background: Psoriasis is the most common inflammatory skin disease, driven by cytokines including IL-12, IL-17, and TNF-α. Patients are frequently colonised with Candida spp., while vitamin D3 deficiency has been implicated in psoriasis pathogenesis and severity. This study compared oral Candida colonisation in patients with psoriasis and healthy controls, evaluated the relationship between vitamin D3 levels and disease severity, and assessed IL-12, IL-17, and TNF-α expression in oral mucosal cells. Methods: Fifty-nine patients with psoriasis and 32 healthy controls were enrolled. Psoriasis severity was assessed using the Psoriasis Area and Severity Index (PASI) and Body Surface Area (BSA). Oral swabs were collected for Candida spp. culture, and serum vitamin D3 levels were measured. Cytokine expression in oral mucosal cells was evaluated by immunohistochemistry and quantified using digital image analysis. Results: Lower serum vitamin D3 levels were associated with greater psoriasis severity. Oral mucosal colonisation by Candida spp. did not differ between patients and controls and was not associated with vitamin D3 levels or psoriasis severity. IL-12 and IL-17 expression was increased in patients with psoriasis compared with controls. IL-12 expression was higher in severe than mild psoriasis, while TNF-α expression was elevated in patients with more severe disease. Conclusions: In this cohort, no significant association was observed between oral Candida colonisation and psoriasis severity or the local cytokine response. In contrast, vitamin D3 deficiency was associated with more severe disease. Increased oral mucosal expression of IL-12, IL-17, and TNF-α indicates the presence of a local inflammatory response within the oral mucosa, which may be consistent with the concept of psoriasis as an inflammatory disorder extending beyond the skin.