Human T Follicular Helper Cells Comprise Subsets Specialized for Help of Distinct B Cell Subsets

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Abstracts

#2203: B Cells in Disease Saturday, June 26 10:45–11:00 am Human T Follicular Helper Cells Comprise Subsets Specialized for Help of Distinct B Cell Subsets Salah-Eddine Bentebibel, Nathalie Schmitl, Rimpei Morita, Jacques Banchereau, Hideki Ueno. Baylor Institute for Immunology Research, Dallas, TX T follicular helper cells (Tfh) represent a Th subset specialized for the help of antibody responses. In contrast to recent progress regarding the phenotype and developmental mechanism of Tfh cells, how Tfh cells regulate B cell responses is less well characterized. In particular, whether Tfh cells are involved in the differentiation of naïve B cells into antibodysecreting cells (ASCs) remains largely unknown. Here we show that human tonsillar Tfh cells comprise subsets specialized for the help of distinct B cell subsets. A subset of Tfh cells, here called Pre-Tfh cells, is specialized for the help of naïve B cells. In contrast, Tfh cells at germinal centers (GC-Tfh cells) are the only Tfh subset able to induce germinal center B (GC-B) cells to produce Igs. Despite the capacity to secrete high levels of Interleukin-21 (IL-21), Pre-Tfh cells failed to help GC-B cells, due to the induction of apoptosis of GC-B cells via FAS/FAS ligand interaction. While Pre-Tfh cells were found exclusively at extrafollicular sites, Pre-Tfh cells expressed Bcl6, a master transcription factor of Tfh cells, at equivalent levels with GCTfh cells. A comprehensive gene expression profiling strongly suggests that pre-Tfh cells are progenitors of GC-Tfh cells. Thus, the differentiation of functional human Tfh cells already occurs at outside of B cell follicles, and such extrafollicular Tfh cells are engaged in the differentiation of naïve B cells. doi:10.1016/j.clim.2010.03.052

The Good, the Bad & the B Cell Saturday, June 26 2:45–4:45 pm OR.33. Transmembrane Activator and Calcium-Modulator and Cyclophilin Ligand Interactor (TACI) Expression is Essential for Human B-cell Tolerance Neil Romberg 1, David Saadoun 1, Rima Rachid 2, Raif Geha 2, Bodo Grimbacher 3, Charlotte Cunningham-Rundles 4, Eric Meffre 1. 1Yale University, New Haven, CT; 2Children's Hospital, Harvard Medical School, Boston, MA; 3Royal Free Hospital and University College London, London, United Kingdom; 4Mount Sinai Medical Center, New York City, NY Common variable immune deficiency (CVID) is a heterogeneous disorder frequently complicated by autoimmunity. To date mutations in several genes have been associated with CVID, the most prevalent of which are mutations in the gene encoding the transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI). Given this association we

have investigated the impact of TACI mutations on human B cell tolerance. We tested the reactivity of recombinant antibodies from single mature naive B cells isolated from healthy human controls and from patients carrying one or two mutated TACI alleles. To accomplish this we utilized single B cell sorting, RTPCR, eukaryotic expression vector cloning/expression, ELISA and an immunoflorescence assay. We found that mature naïve B cells from patients with TACI mutations expressed a high proportion of autoreactive antibodies in comparison with their B cell counterparts from healthy donors. Furthermore, patients displaying two mutated TACI alleles demonstrated higher frequencies of autoreactive B cells compared to patients with a single TACI mutation. Our observations suggest a gene-dosage effect for TACI in the removal of peripheral autoreactive B cells. doi:10.1016/j.clim.2010.03.053

OR.34. Regulation of Immunological Tolerance and Autoimmunity by the Enzyme Sialic Acid Acetylesterase (SIAE) Ira Surolia 1, Stephan Pirnie 2, Vasant Chellappa 2, Cariappa Annaiah 2, Jesse Moya 2, Daphne Bell 2, Khaleda Haider 2, Kendra Taylor 2, Phillip De Jager 2, Tim Behrens 2, David Hafler 2, Bruce Sands 2, Mandakolathur Murali 2, Peter Gregersen 2, Shiv Pillai 2. 1University of Toledo Medical Center, Toledo, OH; 2Massachusetts General Hospital, Boston, MA CD22 activation on the B cell surface leads to negative regulation of the B cell receptor (BCR).CD22 activation, in turn, depends on its ability to bind to alpha 2-6 linked sialic acidcontaining N-glycans.The CD22-CD22 ligand interaction is regulated by 9-o acetylation of the sialic acid. A deacetylation of this moeity is an essential first step in CD22 binding to ligand and inhibiting B cell activation. Sialic Acid Acetylesterase (SIAE) is an enzyme responsible for deacetylating sialic acid ligands of CD22. Mice with a mutation in SIAE exhibit enhanced B cell receptor (BCR) activation, defects in peripheral B cell development, and spontaneously develop antichromatin autoantibodies and glomerular immune complex deposits. Further to studies in mice, heterozygous or homozygous loss of function germline variants of SIAE were identified in 21/820 human subjects with relatively common autoimmune disorders and in 2/648 ethnically matched controls. All heterozygous loss-of-function SIAE mutations tested were capable of functioning in a dominant negative manner.A homozygous secretion-defective mutation in SIAE was catalytically active, lacked the ability to function in a dominant negative manner, and was seen in 8 autoimmune subjects but in no control subjects. The Odds Ratio for inheriting defective SIAE alleles was 8.5 in all autoimmune subjects, 8.3 in subjects with rheumatoid arthritis, and 9.3 in subjects with type I diabetes. SIAE variants represent the first mechanistically confirmed genetic link to defective B cell tolerance in relatively common human autoimmune disorders. We propose that SIAE helps set a threshold for B cell activation by de acetylating the ligand for CD22, and thereby controlling B cell activation and tolerance to self antigens. doi:10.1016/j.clim.2010.03.054