Knops Blood Group System

A number sign (#) is used with this entry because the Knops blood group system represents antigens carried by complement receptor-1 (CR1; 120620) of the erythrocyte cell membrane.

The Knops blood group system comprises 5 high-incidence antigens designated KN1-KN5 (Daniels, 1995). The Knops system antigens are carried on complement receptor-1. In humans, 4 CR1 allotypes of different size are known and all of them express the Knops system antigens. The extracellular domain of CR1, which has 25 potential N-glycosylation sites, can be divided into 30 short consensus repeats (SCRs), each having 60 to 70 amino acids with sequence homology between SCRs ranging from 60 to 90%. The first 28 SCRs are further arranged into 4 longer regions termed long homologous repeats (LHRs), designated LHR-A, LHR-B, LHR-C, and LHR-D and consisting of 7 SCRs each. Tamasauskas et al. (2001) reported studies indicating that the high-incidence Knops system antigens reside within LHR-D and to a lesser extent within LHR-C. Sl(a) (KN4, or Swain-Langley) is involved in malarial rosetting (Rowe et al., 1997), a process associated with cerebral malaria (see 611162), which is the major cause of mortality from Plasmodium falciparum. Reduction in rosette formation occurred with Sl(a-) RBCs. Because the Sl(a-) phenotype is more common in persons of African ancestry (Daniels, 1995), Moulds and Moulds (2000) suggested that this phenotype provided protection against fatal falciparum malaria. The studies of Tamasauskas et al. (2001) suggested that LHR-D may represent an additional malaria interaction region in CR1.