The phenotype is an observable trait above the molecular level, such as anatomy and behavior. It remains the primary data we use to define most species and to understand their phylogenetic history.
Lewis phenotype is one of the blood group antigens such as ABO and RH.
The Lewis blood group system (discovered in 1946 by Mourant) contains 6 antigens encoded on FUT3 and FUT2 genes. According to gene expression, either Le a or Le b antigen will be formed.
These antigens are found on lymphocytes, platelets, endothelium, and epithelium of the kidney, genitourinary, and gastrointestinal tract. They are also present in body fluids except CSF.
According to Le a and Le b presence or absence, there are 4 phenotypes (including one which is almost not present): Le(a+b-), Le(a-b+), Le(a-b-), and rare Le(a+b+).
Lewis phenotype and other blood group antigens relationship
Certain sugars are added to oligosaccharide precursor chains to create the blood group active structures of the Hh, A B O, Lewis, P, and Ii systems. These precursors or chains may be joined to fatty acids via sphingosine to form glycolipids, or they may be joined to a peptide chain via serine or threonine to form glycoproteins. The glycosyl transferase enzymes, which contribute the particular sugar to the glycoprotein or glycolipid precursors, are the direct gene products of each of these blood group systems.
The medical importance of Lewis phenotype
Relationship Between CA 19.9 and the Lewis Phenotype
CA 19.9 (Carbohydrate antigen 19.9) is a tumor marker primarily in patients with gastrointestinal cancer especially pancreatic or cholangiocarcinoma, and other tumors such as ovarian cancer and lung cancer, it also increases in some benign diseases related to the pancreas and liver.
So it is used as a diagnostic test for pancreatic cancer as it has a high sensitivity and is also related to the tumor stage.
But here is the problem, 10% of patients (with the Le(a−b−) phenotype) are unable to synthesize CA 19.9 and, as a result, they get false-negative results even when pancreatic cancer or other malignancies are present.
Most laboratories do not ask for the Le phenotype in their routine samples, as it increases costs and delays the results, and because physicians will often only suggest cancer when the CA 19.9 is abnormally high. However, the exclusion of these patients from measuring CA 19.9 will decrease cost, increase efficiency, and avoid misinterpretations.
Relationship Between H.pylori and the Lewis Phenotype
Infection with H.pylori don't relate to the Lewis blood group nor secretor & nonsecretor phenotypes of the host even though the Le b antigen is a receptor for Helicobacter pylori and it increases susceptibility to candida and other pathogens infect the urinary system, in the other hand, the infection may be related to ABO blood group system.
The expression of H.pylori lipopolysaccharide is polymorphic. Autoimmune mechanisms induced by bacterial Lewis expression have been proposed to cause gastritis.
Refrences
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002033
https://www.sciencedirect.com/topics/medicine-and-dentistry/blood-group-lewis-system
https://www.sciencedirect.com/science/article/abs/pii/S0016508597004605
https://academic.oup.com/femspd/article/1/6-7/321/2911598 Assessed and Endorsed by the MedReport Medical Review Board