Nonsecretor

Nonsecretor refers to an individual who does not secrete ABO blood group antigens and related histo-blood group antigens in most bodily fluids, such as saliva, mucus, and milk. This is in contrast to secretors, who express these antigens in secretions. The nonsecretor phenotype is primarily determined by the FUT2 gene, which encodes an alpha(1,2) fucosyltransferase needed to produce the soluble forms of A, B, and H antigens in mucosal surfaces. While all people have ABO antigens on their red blood cells, secretor status affects the presence of these antigens in secretions rather than on red cells.

Genetically, nonsecretor status results from inactivating variants of FUT2. Individuals who are homozygous for a nonfunctional allele (se/se) are nonsecretors, whereas those with at least one functional allele (Se) are secretors. The Lewis system interacts with FUT2 and FUT3 enzymes to influence mucosal Lewis antigens; in secretors, the ABH and Lewis antigen patterns in secretions differ from those in nonsecretors. The frequency of nonsecretors varies by population, commonly estimated around 20% globally, with substantial ethnic variation.

Diagnosis and testing can be performed by analyzing secretions for ABH antigens (e.g., saliva tests) or by genotyping FUT2 variants. The concept is often used in research, anthropology, and certain clinical contexts rather than routine medical practice.

Clinical and epidemiological relevance centers on how secretor status affects interactions with pathogens and the microbiome. Some pathogens, notably certain noroviruses, bind to mucosal antigens that are present in secretors; as a result, nonsecretors may have altered susceptibility to particular infections. Research continues to clarify the role of secretor status in disease risk and host-microbe interactions, but it is not currently a standard diagnostic criterion in routine care.