title: Expansion of the Knops blood group system and subdivision of Sl(a).
abstract: BACKGROUND
  Complement receptor type 1 (CR1), which bears the Knops (Kn [KN]) blood group antigens, is involved in the rosetting of Plasmodium falciparum- infected RBCs with uninfected cells. As a first step in understanding this interaction, the molecular basis for the blood group antigens encoded by CR1 was investigated.
  
  
  METHODS
  An antibody from a white donor who exhibited an apparent anti-Sl(a) was used for population studies of several racial groups. The donor's genomic DNA was sequenced to identify the Sl(a) mutation and other mutations.
  
  
  RESULTS
  The donor with anti-Sl(a) typed as Sl(a+) with some sera and had the CR1 genotype AA at bp 4828 (R1601). However, she was homozygous for a new mutation (GG) at bp 4855 changing amino acid 1610 from S1610 to T1610 (S1610T). This mutation occurred in heterozygous form in eight white and one Asian donor. The site is only nine amino acids from the previously described Sl(a) polymorphism and appears to produce a new conformational epitope.
  
  
  CONCLUSIONS
  The antigen formerly known as Sl(a) can now be subdivided. A new terminology is proposed that recognizes both linear and conformational epitopes on the CR1 protein. At amino acid 1601, Sl 1 (Sl(a)) is represented by R, Sl 2 (Vil) is represented by glycine, and Sl 3 requires both R1601 and S1610. Sl 4 and Sl 5 are hypothetical epitopes represented by S1610 and T1610, respectively.
authors.affiliation: Department of Microbiology and Immunology, MCP Hahnemann University School of Medicine, Philadelphia, Pennsylvania 19129, USA. moulds@drexel.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Moulds
authors.forename: P A
authors.initials: PA
authors.lastname: Zimmerman
authors.forename: O K
authors.initials: OK
authors.lastname: Doumbo
authors.forename: D A
authors.initials: DA
authors.lastname: Diallo
authors.forename: J P
authors.initials: JP
authors.lastname: Atkinson
authors.forename: M
authors.initials: M
authors.lastname: Krych-Goldberg
authors.forename: D E
authors.initials: DE
authors.lastname: Hourcade
authors.forename: J J
authors.initials: JJ
authors.lastname: Moulds
mesh_terms: D000595:Amino Acid Sequence; D000954:Antigens, Surface / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D044466:Asian People; D044383:Black People; D001789:Blood Group Antigens / Q000235:genetics* / Q000276:immunology; D003001:Cloning, Molecular; D016384:Consensus Sequence; D000939:Epitopes / Q000737:chemistry; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D007518:Isoantibodies / Q000097:blood; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009693:Nucleic Acid Hybridization; D015345:Oligonucleotide Probes; D016133:Polymerase Chain Reaction; D011951:Receptors, Complement / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D020449:Repetitive Sequences, Amino Acid; D017422:Sequence Analysis, DNA; D044465:White People
chemical_list: D000954:Antigens, Surface; D001789:Blood Group Antigens; D000939:Epitopes; D007518:Isoantibodies; D015345:Oligonucleotide Probes; D011951:Receptors, Complement