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Janda, Ales; Schwarz, Klaus; Burg, Mirjam van der; Vach, Werner; Ijspeert, Hanna; Lorenz, Myriam Ricarda; Elgizouli, Magdeldin; Pieper, Kathrin; Fisch, Paul; Hagel, Joachim; Lorenzetti, Raquel; Seidl, Maximilian; Roesler, Joachim; Hauck, Fabian; Traggiai, Elisabetta; Speckmann, Carsten; Rensing-Ehl, Anne; Ehl, Stephan; Eibel, Hermann; Rizzi, Marta (2016): Disturbed B-lymphocyte selection in autoimmune lymphoproliferative syndrome. In: Blood, Vol. 127, No. 18: pp. 2193-2202
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Abstract

Fas is a transmembrane receptor involved in the maintenance of tolerance and immune homeostasis. In murine models, it has been shown to be essential for deletion of autoreactive B cells in the germinal center. The role of Fas in human B-cell selection and in development of autoimmunity in patients carrying FAS mutations is unclear. We analyzed patients with either a somatic FAS mutation or a germline FAS mutation and somatic loss-of-heterozygosity, which allows comparing the fate of B cells with impaired vs normal Fas signaling within the same individual. Class-switched memory B cells showed: accumulation of FAS-mutated B cells;failure to enrich single V, D, J genes and single V-D, D-J gene combinations of the B-cell receptor variable region;increased frequency of variable regions with higher content of positively charged amino acids;and longer CDR3 and maintenance of polyreactive specificities. Importantly, Fas-deficient switched memory B cells showed increased rates of somatic hypermutation. Our data uncover a defect in B-cell selection in patients with FAS mutations, which has implications for the understanding of the pathogenesis of autoimmunity and lymphomagenesis of autoimmune lymphoproliferative syndrome.