Antibodies in saliva may indicate future health risks.
White blood cells secrete immunoglobulins (Ig), or antibodies. These proteins are essential for combating infectious disease. They circulate in the body and tag, destroy and/or neutralize bacteria, viruses and other harmful or foreign materials. They do this by coating foreign materials, thus marking them for destruction or neutralization.
Secretory IgA (sIgA) is secreted at the mucosal surfaces such as the mouth, nose and gastrointestinal tract, and can be measured in saliva.
SIgA is the first line of defense against infection at these surfaces, where it prevents colonization by microbes. It defends against viral and bacterial infections of the upper respiratory tract (URTIs), such as colds and influenza.
However, the relationship between sIgA and health is complex and sometimes surprising. For example, in the case of oral health, lower levels of sIgA appear to be a risk marker for dental caries and decay, whereas high levels are associated with current oral infection.
Researchers from the University of Birmingham in the UK surveyed adults from the eldest cohort of the West of Scotland Twenty-07 Study. They wanted to examine associations between secretory immunoglobulin A (sIgA) in saliva and mortality rates in the general population.
Low secretion rate indicates higher mortality
The 639 participants' saliva was sampled in 1995 when they were aged 63 years. Their IgA secretion rate was measured and the mortality rate was tracked over the following 19 years.
Adjustments were made for gender, assay batch, household occupational group, smoking, medication usage and self-reported health.
IgA secretion rate was negatively associated with all-cause mortality. Further analysis revealed an underlying association with cancer mortality and, in particular, with non-lung cancers.
Saliva sampling is less invasive than blood sampling. If IgA secretion rate in saliva does prove to be a marker of mortality risk, it could be used by professionals as an indicator of overall health during a general checkup.
Dr. Anna Phillips, from the University of Birmingham, explains:
"There are a number of factors that can affect how well we produce antibodies and maintain their levels. There are some that we have no control over, such as age, heritability or illness, but our general state of health can also affect their levels; stress, diet, exercise, alcohol and smoking can all influence those levels."
Dr. Phillips adds that it is not yet known how saliva samples could be used in checkups, as researchers have yet to establish what secretion rate would be considered the threshold level before becoming a cause of concern, otherwise known as the "protective level."
She says that if the level is very low, this could be considered a useful early indicator of risk.
The team hopes to follow up with a larger longitudinal study, to investigate the link with infectious diseases and the development progression of diseases like cancer. This could provide a greater understanding of the mechanisms behind the association found in the study.
Medical News Today reported earlier this year that stress hormones in older people's saliva can indicate future cognitive decline.