Biomarkers in Saliva and Stool

Many soluble factors found in blood can be detected in saliva and stool. Often levels of these factors are found to correlate between body fluids, though the exact relationship between systemic (blood) and local (saliva and stool) immunity is not well established yet. Saliva- and stool-associated factors are produced in the oral cavity and in the gut, which represent mucosal sites that potentially come in direct contact with pathogens. Thus, the levels of mucosal-associated soluble factors can better represent the local immune response at these sites.

It is becoming clear now that saliva and stool can be used to analyze inflammatory responses as well. In a recent study, 20 possible salivary biomarkers related to obesity were surveyed and the authors found four biomarkers that exhibit significant change with increasing body weight in a pediatric population. Salivary C-reactive protein (CRP), salivary insulin, leptin and adiponectin were found to be different in obese children compared to healthy normal weight children. This data suggests that saliva could be a useful blood surrogate for the study of metabolic complications of obesity in children, where repeated blood sampling can be both traumatic and difficult. The results of this study also provide insight into the early development of metabolic disease in children. (Goodson, Kantarci et al. 2014). In another study, cytokines-chemokines-growth factors (CCGFs) were measured using multiplex bead assays and compared between plasma, saliva and urine collected from 20 male and female healthy volunteers. By analyzing more than one sample types from the same subject would increase the possibility of identifying biomarker(s) for any inflammatory disease. In this study, gender-specific CCGFs were also observed and concentrations of some CCGFs varied between genders. This information is also valuable for biomarker discovery that by combining male and female subjects in a clinical trial would eliminate false discovery of biomarkers (Khan 2012).

The mucosal immune system can be also understood by analyzing stool samples. In a recent study, it is shown that a particular bacterial predominance, such as Bifidobacterium sp., may enhance thymic development and immune responses to both oral and parenteral vaccines early in infancy, whereas a deviation from this pattern, resulting in greater bacterial diversity, may cause systemic inflammation (neutrophilia) and lower vaccine responses. Thus, vaccine responsiveness may be improved by promoting intestinal Bifidobacteria sp. and minimizing dysbiosis early in infancy (Huda, Lewis et al. 2014). Of note, the hallmark of adequate mucosal immune responses is the production of secretory immunoglobulin A (SIgA), which can prevent infection and remove antigen crossing the mucosal barrier.SIgAis also imperative to establish mutualism between host and the intestinal microbiota (Maynard, Elson et al. 2012). Hence measurement of SIgA can help to assess the mucosal immunity.

Despite saliva and stool samples are increasingly studied in order to assess mucosal immune response and/or clinical outcomes, there is still a lack of established methodology to be routinely used in diagnostic laboratories and clinical trials. Therefore our aim is to collect saliva and stool samples using the salimetrics swab and self-stool collection kit from a cohort of 60 volunteers, process and store samples in a standardized manner. Following this, we intend to perform immunological assays such as enzyme-linked immunosorbent assay, multiplex bead assay and Immunocap to correlate the salivary and fecal levels of biomarkers in healthy donors. As this method is non-invasive, we believe that more people will be willing to donate samples. It is also easy to self-collect and it is cost efficient.