Session 4 : Autoimmunity

not received. [12.30–12.50] B cell superantigen-like interaction of a subset of IVIG with phage-displayed human IgG and IgM originating from VH germ-line segments 3-23 and 3-30/3-30.5 Peter Fischer, Stephan Leucht, Awuku Osei, Melanie Hoffmann, Nina Jendreyko, Heike Lerch, Martina M. Uttenreuther-Fischer, Gerhard Gaedicke Laboratory of Molecular Biology, Charité Children’s Hospital, OHC, Humboldt-University, 10117 Berlin, Germany E-mail: [email protected] Intravenous immunoglobulin preparations (IVIG) represent the IgG repertoire of several thousand healthy donors. The beneficial use of IVIG in certain immunodeficiencies and autoimmune diseases has been proven, but it is not clear how IVIG functions at the molecular level. We sequenced 104 IgG and IgM clones specifically reacting with IVIG molecules derived by phage display and IVIG-panning from patients with autoimmune thrombocytopenia (AITP), SLE, Kawasaki disease (KD), Stevens-Johnson-Syndrome, and a healthy individual. Sequencing revealed that the most frequently used VH germline gene segments of all IVIGselected Fabs (70/104, 67%) were 3-23 and 3-30/330.5. In contrast, only 3 out of 33 (9%) unselected controls originated from those genes. Comparing two libraries from a patient with KD prepared before and after IVIG treatment, the reactivity with IVIG was higher for clones generated after the therapy. The combined results suggest a favoured interaction of a subset of IVIG – respectively normal immunoglobulin repertoires – with B cell receptors derived from 3-23 and 3-30/3-30.5 gene segments. Importantly, those are the most frequently rearranged VH germ-line genes among human B cells. As light chains, antigen-specificity and the high variation in CDR3 showed only little influence on the selection by IVIG, this type of interaction is characteristic for a B cell superantigen and may significantly shape the B cell repertoire. Further experiments revealed that despite possible homologies, at least some of the contact residues on Fabs for IVIG must be different from those for the model superantigens Staphylococcal protein A and HIV gp120. The IVIG-selected Fabs may now be used to clone antibodies representative of this IVIG-subset to study their regulatory influence on the B cell repertoire during normal development and disease.