Analysis of complement receptor type 1 expression on red blood cells in negative phenotypes of the Knops blood group system, according to CR1 gene allotype polymorphisms.
BACKGROUND
The KN blood group system, which consists of nine antigen specificities, is located on complement receptor Type 1 (CR1/CD35). CR1, a complement regulatory protein, acts as a vehicle for immune complex clearance. CR1 exhibits a red blood cell (RBC) density polymorphism. CR1 sites on RBCs in normal individuals range from 150 to 1200 molecules per cell. CR1 density polymorphism is regulated by HindIII restriction fragment length polymorphism and Q981H and P1786R polymorphisms in Caucasians. Yet, the role of the different polymorphisms in determining the CR1 density on RBCs remains unknown. The "null" serologic KN phenotype, known as Helgeson phenotype, was reported to be related with a very low CR1 density, less than 150 molecules per cell.


METHODS
The aim of this work was to investigate whether the KN-negative phenotype displayed by 60 individuals was related to the CR1 density by performing the phenotypic and genetic analysis of CR1 and to investigate the molecular background associated with the KN system.


RESULTS
We showed that the Helgeson-like phenotype had a prevalence of 12% in this population. The overall genotype/phenotype concordance was 90%. Among individuals with a KN-negative phenotype, the prevalences of Kn(a-), McC(a-), Sl1-negative, Sl3-negative, and KCAM-negative deduced phenotype were 37, 12, 29, 7, and 24%, respectively.


CONCLUSIONS
From our data, we suggest that the definition of the Helgeson phenotype must be revised, since the latter may be due not only to a very low CR1 density on RBCs, but also to the absence of expression of a high-prevalence KN antigen.
Pham
Bach-Nga
BN
Institut National de la Transfusion Sanguine, Centre National de Référence pour les Groupes Sanguins-INSERM U665, Paris, France. bnpham@ints.fr
Kisserli
Aymric
A
Donvito
Béatrice
B
Duret
Valérie
V
Reveil
Brigitte
B
Tabary
Thierry
T
Le Pennec
Pierre-Yves
PY
Peyrard
Thierry
T
Rouger
Philippe
P
Cohen
Jacques H M
JH
D001789:Blood Group Antigens / Q000235:genetics*; D004912:Erythrocytes / Q000737:chemistry*; D006801:Humans; D010641:Phenotype; D011110:Polymorphism, Genetic; D017463:Receptors, Complement 3b / Q000032:analysis / Q000235:genetics*
D001789:Blood Group Antigens; D017463:Receptors, Complement 3b