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A saliva test can determine the severity of recurrent respiratory infections in children more accurately than the standard blood test. If the saliva contains too few broadly protective antibodies, a child is more likely to suffer from pneumonia. This is reported by researchers from the Radboudumc Amalia Children’s Hospital and the UMC Utrecht Wilhelmina Children’s Hospital in European Journal of Respiratory DiseasesSaliva tests provide valuable information for treatment and are more pleasant for children.
About ten to fifteen percent of all children suffer from recurrent respiratory infections. During hospitalization, blood is taken to look for antibody deficiency as an underlying disease. However, this rarely leads to useful results. “This is a challenge for pediatricians because we really want to help the children,” says pediatric infectiologist and immunologist Lilly Verhagen from the Radboud University Hospital. “That’s why we investigated whether we could find out more about the severity of the disease in other ways. This would be very valuable in determining which children need more care and when it makes sense to administer antibiotics.”
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Comprehensive protection
A study of one hundred children with recurrent respiratory infections shows that saliva measurements indicate the severity of the disease better than blood measurements. “We found no connection between antibodies in the blood and the burden of disease. However, in the saliva we observed broadly protective antibodies that act against a wide range of pathogens. Children with lower concentrations of these antibodies had more severe infections. These antibodies in the saliva are actually a good indicator of the burden of disease,” explains doctoral student Mischa Koenen.
The broadly protective antibodies are present in the respiratory tract of all people; the researchers also found them in siblings and parents of the affected children as well as in healthy caregivers. A high level of these antibodies in saliva is beneficial against respiratory infections. They bind so broadly that researchers found antibodies in the saliva of children before the pandemic that could bind to the SARS-CoV-2 virus.
bacteria
While the broadly protective antibodies are present in large quantities in saliva, they are barely detectable in the blood. “And that’s quite logical,” says Verhagen. “You breathe in different things throughout the day, including many respiratory pathogens, and therefore need a broad spectrum of antibodies in your respiratory tract. In the blood, things are different: Only a few pathogens enter the bloodstream via the intestinal or respiratory mucosa. When that happens, your body benefits more from a strong, targeted immune response.”
In addition to antibodies, the researchers also examined the balance between healthy and potentially harmful bacteria on the mucous membranes of the respiratory tract, the so-called microbiome. They found that a certain bacterium on the nasopharyngeal mucosa is strongly linked to the severity of respiratory infections. This bacterium, called Haemophilus influenzae, also colonizes healthy airways. However, children with a high frequency of this bacterium on the respiratory mucosa are more likely to get sick in winter. This bacterium has already been linked to pneumonia.
Future
Saliva and nasopharyngeal mucosa tests are therefore a huge help in assessing children with recurrent respiratory infections. Koenen explains: “This helps us assess how much care and medication children need and which antibiotic to use, as the current standard is not optimal against Haemophilus influenzae. I expect the initial blood test to remain, but for follow-up appointments, a more child-friendly saliva and nasopharyngeal swab could be used as indicators of the expected respiratory disease burden.”
Saliva testing also offers prospects for new treatments and therapies. The researchers found that flu vaccination increases the amount of broadly protective antibodies in the saliva of healthy caregivers. In addition, the researchers are investigating the long-term possibility of using these antibodies to treat respiratory infections in the future.
Reference: Koenen MH, De Steenhuijsen Piters WAA, De Jonge MI, et al. Polyreactive antibodies in saliva and Haemophilus influenzae are associated with the severity of respiratory infections in young children with recurrent respiratory infections. Eur Respir J. 2024:2400317. doi: 10.1183/13993003.00317-2024
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