Human monoclonal Fab fragments recovered from a combinatorial library bind specifically to the platelet HPA-1a alloantigen on glycoprotein IIb-IIIa.
OBJECTIVE
Certain clinical conditions are related to the presence of platelet-specific alloantibodies in the patient's serum. We studied the molecular diversity of HPA-1a antibodies to analyze some peculiarities of this antibody response.


METHODS
Human antibody Fab fragments that bind to the platelet alloantigen HPA-1a on glycoprotein IIb-IIIa (GPIIbIIIa) were generated by using a recombinant phage display system. We established an immunoglobulin G1, kappa combinatorial library from the peripheral blood lymphocytes of a person undergoing a severe posttransfusion purpura.


RESULTS
Characterization of Fab clones selected from the fifth round of antigen-specific panning of this library demonstrates a highly specific reactivity to the HPA-1a alloantigen. The nucleotide sequence analysis of representative HPA-la-specific clones reveals at least 3 distinct V1 and 3VH gene segments that present an extensive degree of mutation as demonstrated by comparison of gene usage and homologies to the nearest germline genes.


CONCLUSIONS
These human HPA-la-specific Fab reagents should allow us to better understand the molecular mechanism involved in HPA-la alloimmunization.
Proulx
C
C
Canadian Red Cross Society, Québec Transfusion Centre-Montréal, Ste-Foy, Canada.
Chartrand
P
P
Roy
V
V
Goldman
M
M
Décary
F
F
Rinfret
A
A
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D016824:Antigens, Human Platelet / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology*; D000939:Epitopes; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000235:genetics / Q000276:immunology*; D039661:Integrin beta3; D008969:Molecular Sequence Data; D019151:Peptide Library; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000276:immunology*
D000911:Antibodies, Monoclonal; D016824:Antigens, Human Platelet; D000939:Epitopes; C061248:ITGB3 protein, human; D007140:Immunoglobulin Fab Fragments; D039661:Integrin beta3; D019151:Peptide Library; D019039:Platelet Glycoprotein GPIIb-IIIa Complex