Saliva serves as a significant fluid in the oral cavity, containing a complex mix of enzymes, antimicrobial peptides, immunoglobulins, and other proteins. These components collectively protect against microbial overgrowth, facilitate digestion, and support tissue repair. The disruption of salivary protein levels or functionality can impair these protective mechanisms, creating an environment conducive to oral dysbiosis. Gaining a comprehensive understanding of salivary proteins, their functions, and their relationship with oral dysbiosis offers valuable insights into preventive and therapeutic strategies for both oral and systemic health.
The basics of spittle
Saliva helps wash away food particles, neutralize acids, remineralize teeth, and fight bacteria. It consists of approximately 98%–99% water, with the remaining portion containing electrolytes, enzymes such as amylase (which breaks down starches), mucus, antimicrobial agents, and proteins essential for digestion and oral health. Adequate hydration increases saliva production and can dilute acids, providing protection to teeth from decay. Additionally, its growth factors and antimicrobial proteins assist in tissue repair and reducing infections.
Primarily produced by three major salivary glands—the parotid, submandibular, and sublingual glands—along with contributions from smaller glands in the mouth, salivary proteins synthesize saliva using water and nutrients derived from blood. Specifically, the water in saliva originates from the plasma portion of the blood, as salivary glands extract water and electrolytes, such as sodium, potassium, chloride, and bicarbonate, which regulate saliva’s composition and pH. The salivary glands also synthesize specialized proteins and enzymes, using amino acids and other nutrients supplied by the blood. Blood plays a crucial role by delivering oxygen and nutrients to salivary gland cells, enabling them to carry out saliva production.
Saliva formation occurs in two main steps. First, during filtration, plasma water and solutes such as electrolytes are drawn from the bloodstream and filtered into the salivary glands. Next, in the secretion and modification phase, the glands enhance the plasma-derived fluid by adding proteins, enzymes, and other molecules, transforming it into saliva.
Let’s talk proteins
Salivary proteins wear several hats. They operate as defensive agents by inhibiting pathogenic microorganisms, contribute to the maintenance of oral mucosa and tooth enamel health, and stabilize the microbiome. Included in their work they act as microbial interactors by offering binding sites for bacteria. Here’s a breakdown of their operations and participants.
Lysosome breaks down the peptidoglycan (polymer) layer of bacterial cell walls, particularly gram-positive bacteria, which tend to have a thicker peptidoglycan layer as compared to gram-negative bacteria. This enzymatic action weakens the structural integrity of the bacterial cell wall, leading to cell lysis and death.1
Lactoferrin in saliva is a multifunctional glycoprotein that contributes significantly to antimicrobial defense by sequestering iron. It binds free iron with high affinity, depriving bacteria of this essential nutrient required for their growth and metabolic processes. Without access to iron, many pathogenic bacteria struggle to survive, thereby reducing their proliferation and pathogenicity.2
Histatins are a family of potent antifungal peptides and are particularly effective against Candida albicans. Histatins exert their antifungal activity by disrupting fungal cell membranes, impairing intracellular ion balance, and inducing oxidative stress, ultimately leading to fungal cell death.3
Mucins are glycoproteins that facilitate bacterial clearance and offer protection by aggregating bacteria, forming clusters that are more easily removed by swallowing or rinsing (yep, we are swallowing the live and dead ones on the regular), thereby preventing bacterial adherence to oral surfaces. Also, mucins lubricate the oral cavity, creating a protective barrier over the mucosa and teeth, which reduces mechanical stress and minimizes bacterial colonization.4
Amylase is an enzyme in saliva that contributes to both digestive and microbial processes in the mouth. It breaks down starch into maltose and dextrins, initiating carbohydrate digestion. Amylase interacts with oral bacteria by facilitating their adhesion to surfaces, including the salivary pellicle on teeth. This dual role is significant for maintaining oral and digestive health and influences microbial dynamics in the mouth.5
Defensins are antimicrobial peptides that work in innate immunity by disrupting bacterial membranes. They achieve this by integrating into the lipid bilayer of bacterial cells, forming pores that compromise membrane integrity, leading to leakage of cellular contents and eventual bacterial death. Defensins are effective against a wide range of pathogens, including bacteria, fungi, and viruses.6
Lastly, sIgA (secretory immunoglobulin A) is an antibody found in saliva assisting as a primary defense mechanism by preventing bacterial adhesion to oral surfaces, including teeth and mucosal tissues. It binds to pathogens and blocks their ability to adhere. sIgA neutralizes toxins produced by harmful bacteria, and that makes sIgA a nice protector against infections such as caries and periodontal disease.7
In patients, salivary protein levels decrease due to various factors, including physiological, lifestyle, or systemic health conditions, which in turn lead to an oral dysbiotic environment. Conditions such as Sjögren’s or salivary gland dysfunction develop a reduced overall salivary production, which diminishes protein availability. The aging process leads to a decrease in salivary flow and protein secretion. Smoking, excessive alcohol consumption, and poor hydration can alter gland function and protein composition. Individuals with diabetes or autoimmune disorders frequently experience diminished secretion and functionality of salivary proteins.
Additionally, chronic stress impacts neuroendocrine pathways, resulting in altered production. Patients who take anticholinergic drugs, antihypertensives, and antidepressants, which increase the propensity for dry mouth, will experience a reduction in protein secretion. Lastly, dietary habits such as high sugar diets promote an acidic environment that degrades salivary proteins, and deficiencies in vitamins such as A, D, and E, along with some minerals, can affect the protein synthesis and secretion.
Salivary proteins are multifaceted and act as the first line of defense against pathogens through antimicrobial actions, such as breaking down bacterial cell walls, disrupting membranes, sequestering essential nutrients, and neutralizing toxins. Additionally, they support oral homeostasis by facilitating bacterial clearance, lubricating tissues, and promoting tissue repair. Beyond their protective functions, salivary proteins contribute to digestion, microbial balance, and the preservation of tooth enamel and mucosal integrity. Saliva is more than a digestive fluid—it’s the secret sauce for oral and systemic health.
Editor's note: This article appeared in the April/May 2025 print edition of RDH magazine. Dental hygienists in North America are eligible for a complimentary print subscription. Sign up here.
