Genetic structure of alphaIIbbeta3-binding phage antibodies derived from patients with autoimmune pathologies

The goal of this study was to use the powerful phage-display technology to study anti-alphaIIbbeta3 autoantibody response at the molecular level in polytransfused Glanzmann thrombasthenia (GT) and autoimmune thrombocytopenic purpura (AITP) patients. We have isolated human single-chain IgG alphaIIbbeta3 binding fragments from the B cells of a GT and two AITP patients, possessing serum IgG Abs against alphaIIbbeta3. Selection was performed by phage-display on activated platelets, alphaIIbbeta3-expressing CHO cells and purified form of the alphaIIbbeta3 integrin. The distribution of the point mutations in the complementarity-determining regions (CDR) and framework regions (FR) in the nucleotide sequences of the VH and VL genes of selected alphaIIbbeta3-specific clones revealed a high level of extensive hypermutations in the CDR, indicating the diversity of antigen-driven immune response. Moreover, alignment analyses of CDR3 portions pointed to motifs other than the well-known RGD or KQAGDV integrin-binding sequences whose sequences could be used for further functional studies.