Non-invasive detection of RSV specific immunoglobulins M, A and G in saliva of subjects in Singapore

Background: Early-life respiratory syncytial virus (RSV) infection has been linked to a higher risk to develop asthma later in life. Many healthy individuals carry RSV viruses in their respiratory systems without developing disease. Measurement of RSVspecific antibodies could provide insights to identify subjects who respond adequately against RSV infection and are able to control it and thus might be at lower risk for asthma development. The gold standard to determine specific responses against RSV by measuring titers of specific antibodies in plasma of blood samples may impose a challenge when it comes to blood collection from infants, children and the elderly, especially in situations when repeated samplings are required. The aim of this study was to compare the anti RSV antibodies in plasma and saliva samples in order to explore the use of saliva as a tool for antibody response against RSV. Method: Paired saliva and stool samples were collected from 65 volunteers aged 0- 46 years after the ethical approval from the PIEC, Singapore. Of these 65 subjects 6 subjects also donated their blood for plasma analysis. Volunteers were deemed healthy at the point of sample collection. Commercial ELISA kits (Neoscientific, Cambridge, Massachusetts) were used to determine RSV-specific antibodies (IgA, IgG and IgM) in the samples. Results: There was a linear correlation between 6 plasma samples and their corresponding saliva samples. 58.5% of the volunteers displayed specific antibodies against RSV in saliva. The ranges in saliva were 27-542 μg/ml for RSV-specific IgA, 23-336 μg/ml for RSV-specific IgG and 71-2594 μg/ml for RSV-specific IgM. All volunteers who were positive for RSV antibodies in saliva also had RSV-specific IgM in their samples. RSV-specific IgM also appeared to be the predominant antibody isotype in saliva. 95% of the RSV specific IgM positive samples contained both RSVspecific IgA and IgG as well. Only one sample contained high concentrations of RSV-specific IgM (596 ug/ml) without any other RSV-specific antibody isotype, indicating a possible recent infection. RSV-specific antibodies were not detectable in any of the stool samples. Conclusion: We demonstrated that RSVspecific IgM, IgG and IgA can be detected in saliva samples. Importantly, titers in saliva were linearly correlated with those measured in plasma samples. A further study with controlled set-up is needed to validate the use of saliva as a tool for antibody response against RSV.