A secretor is an individual who expresses their ABO blood group antigens (A, B, or H) not only on their red blood cells but also in various other bodily fluids and secretions. These include saliva, tears, sweat, mucus, breast milk, urine, and semen. This characteristic is determined by a specific genetic trait, distinguishing individuals as either secretors or non-secretors. This expression in bodily fluids is distinct from, yet related to, the antigens present on red blood cells.
Understanding Secretor Status
The ability to secrete ABO blood group antigens into bodily fluids is governed by the FUT2 gene, also known as the secretor gene. This gene encodes an enzyme responsible for creating the H antigen, a precursor to the A and B antigens, in secretions. Individuals with at least one functional copy of the FUT2 gene are classified as secretors, meaning their bodily fluids contain these soluble ABO antigens.
Conversely, those with two non-functional copies of the FUT2 gene are non-secretors. In these individuals, the enzyme produced by the FUT2 gene is inactive, preventing the formation of the H antigen in bodily fluids. As a result, non-secretors do not express soluble ABO antigens in their secretions, even though these antigens are present on their red blood cells. This distinction emphasizes that secretor status relates to where these antigens are expressed throughout the body. Approximately 75% to 80% of Caucasian populations are secretors, while 20% to 25% are non-secretors.
The FUT2 gene allows the H antigen to form in secretions, which can then be modified by enzymes from the ABO gene to produce A or B antigens corresponding to an individual’s blood type. For example, a person with Type A blood who is a secretor will have A antigens in their saliva and other fluids.
Determining Your Secretor Status
Determining an individual’s secretor status often involves analyzing bodily fluids for the presence of ABO blood group antigens. One common method is saliva testing, which identifies soluble antigens. In this serologic approach, a saliva sample is combined with reagents containing antibodies specific to A, B, or H antigens.
Red blood cells expressing these antigens are then added to the mixture. If the person is a secretor, the antibodies will bind to the antigens in their saliva, preventing them from reacting with the red blood cells, which indicates a positive result. If no antigens are present in the saliva, the antibodies will cause the red blood cells to clump together, indicating a non-secretor status.
Genetic testing offers a more definitive way to determine secretor status by analyzing an individual’s DNA for the FUT2 gene. This method involves examining specific genetic markers, such as the rs601338 variant within the FUT2 gene. A genotype of “AA” at this locus indicates a non-secretor status, while “GA” or “GG” genotypes suggest a secretor status. Some direct-to-consumer genetic testing services can provide this information from a DNA sample, typically collected via a cheek swab.
Health Connections of Secretor Status
Secretor status can influence an individual’s susceptibility to certain infections. Non-secretors often exhibit decreased vulnerability to most strains of Norovirus, a common cause of gastroenteritis, because these viruses use histo-blood group antigens (HBGAs) in the digestive tract mucosa for attachment. Similarly, the colonization of Helicobacter pylori, a bacterium linked to ulcers, tends to be lower in non-secretors.
Conversely, non-secretor status has been associated with increased susceptibility to certain other pathogens. This includes a higher likelihood of infections from organisms such as Candida, Haemophilus influenza, Neisseria meningitidis, and Streptococcus pneumoniae. Additionally, some studies indicate that non-secretors may experience an increased risk of mumps infection.
Secretor status also plays a role in the composition and diversity of an individual’s gut microbiome. For secretors, the continuous supply of secreted blood type antigens into the digestive tract mucus provides a food source for certain beneficial gut bacteria. These specific carbohydrates, or oligosaccharides, can influence the types and balance of microorganisms residing in the gut, potentially promoting a more stable and diverse bacterial ecosystem.
Beyond infectious diseases and the gut microbiome, secretor status has been linked to certain chronic conditions. Non-secretors may have an increased risk of developing Type 1 diabetes and inflammatory bowel diseases such as Crohn’s disease. There are also associations with an elevated risk of kidney disease in non-secretors. It is important to remember that these are observed associations, and many interacting factors contribute to overall health and disease susceptibility.