Candida Infections: The Role of Saliva in Oral Health-A Narrative Review

Abstract

Candida species, particularly Candida albicans, are causative agents of oral infections to which immunocompromised patients are especially susceptible. Reduced saliva flow (xerostomia) can lead to Candida overgrowth, as saliva contains antibacterial components such as histatins and β-defensins that inhibit fungal growth and adhesion to the oral mucosa. Candida adheres to host tissues, forms biofilms, and secretes enzymes required for tissue invasion and immune evasion. Secretory asparaginyl proteinases (Saps) and candidalysin, a cytolytic peptide toxin, are vital to Candida virulence, and agglutinin-like sequence (Als) proteins are crucial for adhesion, invasion, and biofilm formation. C. albicans is a risk factor for dental caries and may increase periodontal disease virulence when it coexists with Porphyromonas gingivalis. Candida infections have been suggested to heighten the risk of oral cancer based on a relationship between Candida species and oral squamous cell carcinoma (OSCC) or oral potentially malignant disorder (OPMD). Meanwhile, β-glucan in the Candida cell wall has antitumor effects. In addition, Candida biofilms protect viruses such as herpesviruses and coxsackieviruses. Understanding the intricate interactions between Candida species, host immune responses, and coexisting microbial communities is essential for developing preventive and therapeutic strategies against oral Candida infections, particularly in immunocompromised individuals.

Keywords: Candida species; biofilm; immunity; oral diseases; saliva.

Figure 1

Two primary invasion methods are induced endocytosis and active penetration. Active penetration relies on hyphal elongation and secreted enzymes, such as secreted aspartyl proteinases (Saps), which can degrade interepithelial junctions. Abbreviations: Als, agglutinin-like sequence; EGFR, epidermal growth factor receptor; HER2, human epidermal growth factor receptor 2; CR3, complement receptor 3; Hwp1, hyphal wall protein 1; Sap, secretory aspartyl proteinase; ECM, extracellular matrix.

Figure 2

Receptors for components of Candida species. NF-κB and AP-1 are transcription factors, which play an important role in cytokine production. Abbreviations: Als, agglutinin-like sequence; EGFR, epidermal growth factor receptor; EphA2, ephrin type-A receptor 2; CR3, complement receptor 3; TLR, Toll-like receptor; Syk, spleen tyrosine kinase; NF-κB, nuclear factor-κB; MAPK, mitogen-activated protein kinase; AP-1, activator protein-1.