Evidence for an influence of secretor status on levels of the ABO-isoantibodies in serum.

Sir,

ABO-isoantibodies are naturally occurring regular alloantibodies. They are developed during the early childhood of 3 months and remain good through adult life. The reactivity strength varies from one individual to another under the influence of the factors like age, sex.[1] The secretor status, characterized by a presence of ABH blood group antigens in saliva, is controlled by gene Se (FUT2) which codes for enzyme glycosyltransferase that assembles sugar molecules to confer the ABH blood groups antigen in body secretions including saliva.[2] The recessive allele se makes an individual nonsecretor in the homozygous state. In order to find an influence of the secretor status on the levels of the ABO-isoantibodies, we tested 140 students at the Institute of Health Science, Muscat, in the age group of 17 years and above. Secretor status was determined on saliva using hemagglutination inhibition technique and was correlated with the level of the isoantibodies. The titer value of ≥ 128 was considered as high level while that of ≤ 64 was taken a low.[1] Statistical analysis was performed by 2 × 2 contingency table with Fisher's exact test. Of 140 subjects tested, 103 (73.6%) individuals were secretor and 37 (26.4%) were nonsecretor. Ninety-four of the participants showed high titer while 46 of those were with a low titer of isoantibodies. Interestingly, as many as 85 persons with high titer values belonged to the “secretor” category, whereas, 28 individuals classified as “nonsecretor” had a low level of the antibodies. Statistical analysis showed the association as extremely significant (P = 0.0001) [Table 1].

Table 1

Correlation of secretor status and the levels of ABO-isoantibodies in Omani youths

A presence of hemolytic isoantibodies correlates with high titer. Grundbacher and Shreffler[3] observed lower values of hemolytic anti-B among nonsecretors. In a similar note, Dube et al.[4] found a higher level of cold auto-anti-I among the secretors. Our observations on secretor status and the level of isoantibodies accord with these reported findings.

Isoantibodies are stimulated by environmental antigens including microorganisms and provide natural immunity to a person. The individuals classified as secretors with a greater level of isoantibodies may have the advantage of being protected from invading pathogens that may possess blood groups like antigen. Gershowitz and Neel[5] reviewed the rheumatic disease was frequently found among nonsecretors. Etiology of rheumatic disease is known for its prior exposure to streptococcal infection, and therefore, it is conceivable that the nonsecretors with a lower level of isoantibodies and immunoglobulins may have a lower resistance to infection. It appears that the gene responsible for Secretor status has a greater role to play beyond just exerting secretion of ABO antigens in saliva.