A Novel Variant of the Human Blood Group K1 Antigen

Abstract

A discrepancy in duplicate anti-K1 typing in a parentage case led to the discovery of an unusual K1 blood group antigen. Red blood cells from the propositus (JC) express a rare variant of the K1 antigen that is detectable by only 8 of 72 sera containing anti-K1. Absorption and elution studies using reactive anti-K1 confirmed the presence of a K1 antigen. Nonreactive anti-K1 was not absorbed by or eluted from JC’s red blood cells. Red cells from 3 of the propositus’s siblings also had the variant K1 antigen. The variant antigen exhibited qualitative as well as quantitative differences as compared to normal K1, and we have named it K1var.

A KEL gene encoding serine at position 193 of the Kell glycoprotein results in expression of KEL1 antigen

“…KEL1, the original Kell antigen, is no exception. There is one report of an apparent qualitative KEL1 variant in a KEL:1 individual with a KEL1‐like antibody 11 and two other reports of weak or variant KEL1 that were not associated with anti‐KEL1 production 12,13 . None of these variants was investigated at the molecular level.…”

Another example of a KEL1 variant red cell phenotype due to a threonine to serine change at position 193 of Kell glycoprotein

“…An unusual KEL1 blood group antigen phenotype has been described, KEL1 variant 1,2 . This antigen is detected by some, but not all, serum samples containing anti‐KEL1.…”

“…This antigen is detected by some, but not all, serum samples containing anti‐KEL1. The expression of other Kell blood group system antigens is normal on variant RBCs; 1,2 however, in subjects with K mod , McLeod, and K:13 phenotypes the expression of all Kell blood system antigens is reduced 3‐6 . In addition the K:3,4 phenotype has a cis ‐modifying effect on KEL group antigens that are cis to K:3 (Kp a ) 7 …”

K phenotyping using a PK-7200 automated analyzer

“…8 However, there are unusual K and k phenotypes that require adsorption and elution studies in order to confirm true RBC phenotypes. 9 The weak expression of the K antigen is a rare event that occurs in the McLeod and Gerbich-negative phenotypes. 10 It can be detected also in a variety of phenotypes in which all high-frequency Kell and para-Kell antigens are depressed.…”