Researchers from the National Institute of Dental and Craniofacial Research have suggested that HIV transmission may be facilitated by the tonsils, which contain high numbers of immune cells that may be easily accessible to the virus. Writing in The American Journal of Pathology, the researchers explain that HIV spreads mainly through sexual contact of mucosal surfaces, which the virus must cross to come in contact with underlying immune cells for infection to occur. While the oral mucosal surfaces are largely protected by their thickened exterior and the defensive proteins present in saliva, transmission appears to be more easily facilitated by the tonsils.
Led by Dr. Sharon M. Wahl, the researchers compared the gene expression profiles of tonsils and oral gingiva. Although many of the genes examined showed similar expression patterns between the two oral sites, differences were observed. Notably, several genes related to immune functions, including HIV co-receptor CXCR4, displayed significantly higher expression in the tonsils while gingiva more strongly expressed keratin genes, which thicken the tissue and provide barrier protection.
The study found that the decreased amount of keratin and antiviral proteins in the tonsils renders the tissue more permeable to foreign invaders. Additionally, the group found that the CXCR4 protein was expressed on gingiva, oral mucosa and tonsils, but the expression was strongest in tonsils. Levels of additional molecules that may bind and entrap HIV, such as complement receptors and FcR, were also higher in the tonsils.
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Source: American Journal of Pathology
