title: Localization of Knops system antigens in the long homologous repeats of complement receptor 1.
abstract: BACKGROUND
  The Sl(a) (Knops system) located on complement receptor 1 (CR1) has been associated with malarial rosetting, a process associated with severe malarial infections. Moreover, the long homologous repeats (LHRs) B and C of CR1 were implicated in rosette formation. As a step toward mapping the location of Knops system antigens, truncated CR1 proteins have been expressed and their ability to inhibit antibodies to the high-incidence Knops system antigens was assessed.
  
  
  METHODS
  Individual LHRs (A, B, C, and D) of CR1 of the common CR1*1 (F) allotype were expressed as secreted forms in 293T cells. Their abilities to specifically neutralize Knops system antibodies were tested by both hemagglutination and flow cytometry.
  
  
  RESULTS
  Three examples of anti-Kn(a) (n = 6) were almost completely inhibited by LHR-C and three by LHR-D. Two examples of anti-McC(a) (n = 2) and seven examples of anti-Sl(a) (n = 8) were inhibited by LHR-D. Both examples of anti-Yk(a) (n = 2) were partially inhibited by LHR-D.
  
  
  CONCLUSIONS
  The high-incidence Knops system antigens reside within LHR-D and to a lesser extent within LHR-C. Because of the role of Sl(a) antigen in malaria rosetting, these results indicate that LHR-D may represent an additional malaria interaction region in CR1.
authors.affiliation: Immunochemistry Laboratory, New York Blood Center, New York, New York 10021, USA.
authors.forename: D
authors.initials: D
authors.lastname: Tamasauskas
authors.forename: V
authors.initials: V
authors.lastname: Powell
authors.forename: A
authors.initials: A
authors.lastname: Schawalder
authors.forename: K
authors.initials: K
authors.lastname: Yazdanbakhsh
mesh_terms: D000911:Antibodies, Monoclonal / Q000187:drug effects / Q000494:pharmacology; D001789:Blood Group Antigens / Q000276:immunology*; D002460:Cell Line; D002874:Chromosome Mapping; D004912:Erythrocytes / Q000187:drug effects / Q000276:immunology; D015870:Gene Expression; D006801:Humans; D007518:Isoantibodies / Q000187:drug effects / Q000276:immunology; D007519:Isoantigens / Q000235:genetics* / Q000276:immunology; D010446:Peptide Fragments / Q000494:pharmacology; D017463:Receptors, Complement 3b / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics*; D020449:Repetitive Sequences, Amino Acid; D017386:Sequence Homology, Amino Acid; D012995:Solubility
chemical_list: D000911:Antibodies, Monoclonal; D001789:Blood Group Antigens; D007518:Isoantibodies; D007519:Isoantigens; D010446:Peptide Fragments; D017463:Receptors, Complement 3b