Role in Blood Groups
The Knops antigen was the 25th blood group system recognized and consists of the single antigen York (Yk) a with the following allelic pairs:
- Knops (Kn) a and b
- McCoy (McC) a and b
- Swain-Langley (Sl) 1 and 2
The antigen is known to lie within the CR1 protein repeats and was first described in 1970 in a 37-year-old Caucasian woman. Racial differences exist in the frequency of these antigens: 98.5% and 96.7% of American Caucasians and Africans respectively are positive for McC(a). 36% of a Mali population were Kn(a) and 14% of exhibited the null (or Helgeson) phenotype compared with only 1% in the American population. The frequencies of McC (b) and Sl (2) are higher in Africans compared with Europeans and while the frequency of McC (b) was similar between Africans from the USA or Mali, the Sl (b) phenotype is significantly more common in Mali - 39% and 65% respectively. In Gambia the Sl (2)/McC(b) phenotype appears to have been positively selected - presumably due to malaria. 80% of Papua New Guineans have the Helgeson phenotype and case control studies suggest this phenotype has a protective effect against severe malaria.
Read more about this topic: Complement Receptor 1
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