Optimal assay conditions for quantifying fibronectin in saliva

Fibronectin (Fn) is a glycoprotein that is present in many body fluids and tissues in both physiological and pathological conditions. It can also be detected in the saliva, although only in very small quantities and frequently in broken chains. It induces bacterial aggregation and its levels fall when those of cariogenic or periodontal pathogenic bacteria rise. The infective capacity of the saliva of patients infected by human immunodeficiency virus (HIV) has been linked to the levels of this protein. In some chronic conditions of the oral mucosa,such as oral lichen planus, the concentration of salivary fibronectin is lower than usual. Fibronectin quantity also varies in the presence of some tumours, such as oral squamous cell carcinoma, although it cannot be considered a specific factor.

Due to the low Fn concentration in saliva and its lability in the soluble form, sample collection and conservation conditions are extremely important. The aim of this study is therefore to standardise these conditions so that the Fn can be quantified in an optimum manner.

The Fn concentration in human saliva was determined in 20 healthy subjects aged between 28 and 54 by means of the ELISA technique and the concentration of the protein in fresh samples kept at 4 grades C for 24 hours was compared with that of frozen samples kept at 40 grades C below 0, for different periods of time.

After comparing different ways of conserving the saliva samples, we found that the optimum conditions were to collect the samples in glass tubes and to quantify them immediately after collection or conserve them at 4 grades C and quantify them within a maximum of 24 hours. Freezing and later thawing for quantification induced losses of up to 60% of the protein.