Recombinant human natural autoantibodies against GPIIb/IIIa inhibit binding of autoantibodies from patients with AITP.
Autoimmune thrombocytopenic purpura (AITP) is caused by autoantibodies predominantly against platelet membrane glycoproteins (GP) IIb/IIIa and GPIb/IX. Naturally occurring autoantibodies have been described against a variety of autoantigens; it has been suggested that perturbation of their regulation may be associated with autoimmune diseases. Using a combinatorial Fab phagemid library from an individual immunized with human RhD+ red blood cells, we evaluated the presence of natural anti-GPIIb/IIIa autoantibodies as well as their relation to AITP-associated anti-GPIIb/IIIa autoantibodies. Selection on native GPIIb/IIIa and characterization of positive clones by inhibition studies against murine monoclonal anti-GPIIb/IIIa antibodies and by DNA analysis revealed the presence of two distinct recombinant anti-GPIIb/IIIa autoantibodies, which partially inhibited binding of affinity-purified platelet-associated autoantibodies from 8/12 AITP patients. Our results demonstrated that GPIIb/IIIa-specific Fab directed against conformational epitopes within the GPIIb/IIIa complex may be cloned from the genome of an individual immunized with RhD+ red blood cells, who was not affected by AITP. The partial inhibition of binding of platelet-associated autoantibodies from AITP patients to GPIIb/IIIa by the recombinant anti-GPIIb/IIIa phage clones suggests recognition of closely related antigenic epitopes. These phage clones may represent down-regulated, potentially pathological autoantibodies and could be used as new tools for investigation of AITP.
Escher
R
R
Department of Medicine, University Hospital, Bern, Switzerland.
Müller
D
D
Vogel
M
M
Miescher
S
S
Stadler
B M
BM
Berchtold
P
P
D000595:Amino Acid Sequence; D001323:Autoantibodies / Q000378:metabolism*; D000939:Epitopes; D006801:Humans; D008969:Molecular Sequence Data; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000276:immunology*; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000276:immunology*
D001323:Autoantibodies; D000939:Epitopes; D019039:Platelet Glycoprotein GPIIb-IIIa Complex