Kell Blood Group

ScienceTopping | Sept 15, 2024

Kell Antigen

Kell blood group has a variety of 25 antigens due to the polymorphic nature of KEL gene.

IMAGE BY ENES KOÇ/PIXABAY

In the world of blood group, ABO blood group has crowned the ranking in the potency of its antigens, being the most potent immunogenic erythrocyte antigen. Rhesus antigens follow after ABO antigens, and here it comes the third most potent immunogenic antigen — Kell antigen (K antigen) in Kell blood group. Kell blood group has a total of 25 antigens, but there are 2 major antigens which are codominant, namely K and k antigens. K antigen is known as Kell antigens, while k antigen is also known as cellano antigen.

Tracing back to the molecular level, XK gene first produces Kx substance, which is an important precursor for Kell antigen. In order to produce proper Kell antigens, KEL metallo-endopeptidase (KEL gene) located on chromosome 7 is the gene that converts Kx substance into the proper functional Kell antigen. As the result of the polymorphic nature of KEL gene, 25 antigens may be manifested. Just any other antigens on the red blood cells, Kell antigens are glycoproteins embedded in the membrane of red blood cells. Since there are 2 major antigens in Kell blood group, there are 3 phenotypes in general, with K-k+ phenotype as the most common category.

K+k- (with KK genotype)

K+k+ (with Kk genotype)

K-k+ (with kk genotype)

The harm brought about by Kell antigens occurs during pregnancy and blood transfusion under special conditions, just like ABO and Rhesus antigens. First of all, when a Kell negative firstly preganant mother has a Kell positive baby, anti-K antibodies are produced if the baby's blood with Kell antigens mixes with the mother's blood with no Kell antigens, as Kell antigens are recognised as foreign substances to the mother's immune system. However, this still causes no harm to the first baby yet. In the second pregnancy, if the Kell negative mother has a Kell positive baby again, the previously sensitised mother will produce sufficient anti-K antibodies against the Kell antigens of baby's red blood cells. This is the deleterious haemolytic disease of the newborn (HDN).

As for haemolytic transfusion reactions (HTR), Kell negative individual can only receive Kell negative blood. Notwithstanding, Kell positive individual is allowed to receive either Kell positive or Kell negative blood.

Clinical Highlight

Kx substance is the protein precursor for Kell antigens. The absence of Kx substance due to mutation in XK gene results in weakly expressed Kell antigens as seen in the rare X-linked McLeod syndrome. The classical haemotological feature is the red blood cells with abnormal spiky projections, known as acanthocytosis.

McLeod neuroacanthocytosis syndrome typically manifests between 30 and 40 years of age, with the following common conditions.

Cardiomyopathy
Muscular dystrophy
Psychiatric disturbances
Neurological defects, such as loss of reflexes and movement disorders

For the symptomatic management of McLeod syndrome, dopamine-blocking agents such as tiapride and clozapine are used to reduce chorea.

+1 Topping Point

The absence of Kx substance in erythrocyte causes McLeod syndrome, while the absence of Kx substance in white blood cell causes chronic granulomatous disease which is also X-linked. Affected individuals may complain of recurrent bacterial infections, because white blood cells are able to carry out phagocytosis in times of bacterial invasion, but the bacteria are not killed due to the defective phagocyte NADPH oxidase as a result of KEL gene mutation.

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