Secretor (H) antigen increased significantly in the saliva and tracheal aspirate samples of premature neonates in the first weeks of life, indicating increased expression of the secretor gene. Consistent with our hypothesis, low or non-secretor status strongly predicted risk of adverse outcomes that occurred after the first postnatal week, including overall mortality and death in sepsis and NEC cases. Non-secretor genotype was associated with gram negative sepsis, but not overall sepsis. Low H phenotype was also associated with 4-fold increased odds of surgical NEC and 3-fold increased odds of NEC per se. Low H phenotype predicted death whether analyzed as the H antigen O.D. value or as a dichotomous variable generated with CART or receiver operating characteristic analysis, particularly deaths occurring at older postnatal ages. The mortality rate in heterozygote secretors with low H phenotype was similar to the genetic non-secretors, and mortality in heterozygotes with high H phenotype was similar to the dominant secretors. The results are unlikely by bias, because several laboratories were involved, blinded to infant clinical status. Clinical data collection followed a nationally standardized protocol and preceded the laboratory analyses. The results are also unlikely caused by chance: The outcomes were robustly associated with secretor status, significant associations persisted in multivariable models, and risk of mortality increased in a dose-dependent fashion across the non-secretor, heterozygote, and secretor dominant groups.
The secretor gene appears important in early ontogeny. The secretor gene is known to be expressed in fetal epithelial tissues and saliva.9
Uncolonized gut contains limited amounts of H antigen. During the first postnatal weeks, concurrent with bacterial colonization, the intestinal epithelium shows a pronounced increase in fut2
-mRNA and fucosyltransferase activity that can be ablated with intensive antimicrobial administration.17, 18
Amniotic fluid and human milk contain secretor antigens that bathe the fetal and neonatal mucosa.23, 24
In this study, we found that secretor (H) antigen increases postnatally in the saliva and tracheal aspirates of infants born live. Although the mechanisms explaining absent or low H antigen as a biomarker of adverse outcomes in prematurity remains to be determined, potential explanations include correlation with mucosal immaturity or aberrant colonization.
The immature immune system of premature infants increases susceptibility to pathogens that can cause NEC or sepsis.25, 26
Individual risk of infection may vary with the availability of preferred antigen for pathogen attachment to mucosal surfaces. Most noroviruses, many E. coli
, campylobacter and Streptococcus pneumoniae
prefer binding to secretor antigen and thus, may infect secretors more frequently.11–16, 23
However, other pathogens preferentially bind to non-secretor antigens.7, 10, 12
A potential explanation for the findings of our study is increased virulence of pathogens causing NEC or sepsis in non- or low-secretors. However, sepsis case fatality was higher in non- and low-secretors regardless of whether the organism causing sepsis was gram negative or gram positive.
Alternatively, low expression of secretor antigen may contribute to the hyper-inflammatory response that is the hallmark of preterm infants. Non-secretors are reported to have a greater inflammatory response to infection with H. pylori
and renal scarring in acute pyelonephritis compared with secretors.27, 28
Although functional studies of fucosylation are lacking, the regulation of inflammation may be impaired in premature infants in the absence of secretor antigen. Acute phase response results in defucosylation of plasma proteins, including alpha-1 acid glycoprotein, which is involved in regulation of inflammation.29, 30
In the third trimester, the alpha-1 acid glycoprotein in amniotic fluid is highly fucosylated, and contains substantial secretor antigen.24
Secretor phenotype and genotype provide powerful information that cannot be inferred through clinical factors and may help target more effective surveillance and interventions. Measuring these biomarkers could provide a novel approach to prediction of NEC and sepsis outcomes. While the explanation of our findings remains to be determined, a clue may have been provided by the recent report that non-secretor status is associated with Crohn’s Disease, a condition thought to result from an abnormal immune response to intestinal microflora. We thus speculate that non-secretor status may contribute to an aberrant colonization and immune response in some adverse circumstances, such as premature birth. In this initial study, we used extant data and samples. A prospective study has been initiated to confirm these novel biomarkers in relation to neonatal outcomes. Increased understanding of the impact of the secretor gene in prematurity should provide important insights into the pathogenesis of disease progression and infant vulnerability. Greater attention to glycosylation in innate immunity is warranted.