@article{DirksAndresPauletal.2023,
  author    = {Dirks, Johannes and Andres, Oliver and Paul, Luisa and Manukjan, Georgi and Schulze, Harald and Morbach, Henner},
  title     = {IgD shapes the pre-immune na{\"i}ve B cell compartment in humans},
  series = {Frontiers in Immunology},
  volume    = {14},
  journal   = {Frontiers in Immunology},
  doi       = {10.3389/fimmu.2023.1096019},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-304758},
  year      = {2023},
  abstract  = {B cell maturation and immunoglobulin (Ig) repertoire selection are governed by expression of a functional B cell receptor (BCR). Na{\"i}ve B cells co-express their BCR as IgM and IgD isotype. However, the role of the additionally expressed IgD on na{\"i}ve B cells is not known. Here we assessed the impact of IgD on na{\"i}ve B cell maturation and Ig repertoire selection in 8 individuals from 3 different families with heterozygous loss-of-function or loss-of expression mutations in IGHD. Although na{\"i}ve B cells from these individuals expressed IgM on their surface, the IGHD variant in heterozygous state entailed a chimeric situation by allelic exclusion with almost half of the na{\"i}ve B cell population lacking surface IgD expression. Flow cytometric analyses revealed a distinct phenotype of IgD-negative na{\"i}ve B cells with decreased expression of CD19, CD20 and CD21 as well as lower BAFF-R and integrin-β7 expression. IgD-negative B cells were less responsive in vitro after engaging the IgM-BCR, TLR7/9 or CD40 pathway. Additionally, a selective disadvantage of IgD-negative B cells within the T2 transitional and mature na{\"i}ve B cell compartment as well as reduced frequencies of IgMlo/- B cells within the mature na{\"i}ve B cell compartment lacking IgD were evident. RNA-Ig-seq of bulk sorted B cell populations showed an altered selection of distinct VH segments in the IgD-negative mature na{\"i}ve B cell population. We conclude that IgD expression on human na{\"i}ve B cells is redundant for generation of na{\"i}ve B cells in general, but further shapes the naive B cell compartment starting from T2 transitional B cells. Our observations suggest an unexpected role of IgD expression to be critical for selection of distinct Ig VH segments into the pre-immune Ig repertoire and for the survival of IgMlo/- na{\"i}ve B cells known to be enriched in poly-/autoreactive B cell clones.},
  language  = {en}
}
@article{DirksHaaseCantaertetal.2022,
  author    = {Dirks, Johannes and Haase, Gabriele and Cantaert, Tineke and Frey, Lea and Klaas, Moritz and Rickert, Christian H. and Girschick, Hermann and Meffre, Eric and Morbach, Henner},
  title     = {A novel AICDA splice-site mutation in two siblings with HIGM2 permits somatic hypermutation but abrogates mutational targeting},
  series = {Journal of Clinical Immunology},
  volume    = {42},
  journal   = {Journal of Clinical Immunology},
  number    = {4},
  doi       = {10.1007/s10875-022-01233-5},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-324253},
  pages     = {771-782},
  year      = {2022},
  abstract  = {Hyper-IgM syndrome type 2 (HIGM2) is a B cell intrinsic primary immunodeficiency caused by mutations in AICDA encoding activation-induced cytidine deaminase (AID) which impair immunoglobulin class switch recombination (CSR) and somatic hypermutation (SHM). Whereas autosomal-recessive AID-deficiency (AR-AID) affects both CSR and SHM, the autosomal-dominant form (AD-AID) due to C-terminal heterozygous variants completely abolishes CSR but only partially affects SHM. AR-AID patients display enhanced germinal center (GC) reactions and autoimmune manifestations, which are not present in AD-AID, suggesting that SHM but not CSR regulates GC reactions and peripheral B cell tolerance. Herein, we describe two siblings with HIGM2 due to a novel homozygous AICDA mutation (c.428-1G > T) which disrupts the splice acceptor site of exon 4 and results in the sole expression of a truncated AID variant that lacks 10 highly conserved amino acids encoded by exon 4 (AID-ΔE4a). AID-ΔE4a patients suffered from defective CSR and enhanced GC reactions and were therefore indistinguishable from other AR-AID patients. However, the AID-ΔE4a variant only partially affected SHM as observed in AD-AID patients. In addition, AID-ΔE4a but not AD-AID patients revealed impaired targeting of mutational hotspot motives and distorted mutational patterns. Hence, qualitative defects in AID function and altered SHM rather than global decreased SHM activity may account for the disease phenotype in these patients.},
  language  = {en}
}
@article{FortmannDirksGoedickeFritzetal.2022,
  author    = {Fortmann, Mats Ingmar and Dirks, Johannes and Goedicke-Fritz, Sybelle and Liese, Johannes and Zemlin, Michael and Morbach, Henner and H{\"a}rtel, Christoph},
  title     = {Immunization of preterm infants: current evidence and future strategies to individualized approaches},
  series = {Seminars in Immunopathology},
  volume    = {44},
  journal   = {Seminars in Immunopathology},
  number    = {6},
  doi       = {10.1007/s00281-022-00957-1},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-324261},
  pages     = {767-784},
  year      = {2022},
  abstract  = {Preterm infants are at particularly high risk for infectious diseases. As this vulnerability extends beyond the neonatal period into childhood and adolescence, preterm infants benefit greatly from infection-preventive measures such as immunizations. However, there is an ongoing discussion about vaccine safety and efficacy due to preterm infants' distinct immunological features. A significant proportion of infants remains un- or under-immunized when discharged from primary hospital stay. Educating health care professionals and parents, promoting maternal immunization and evaluating the potential of new vaccination tools are important means to reduce the overall burden from infectious diseases in preterm infants. In this narrative review, we summarize the current knowledge about vaccinations in premature infants. We discuss the specificities of early life immunity and memory function, including the role of polyreactive B cells, restricted B cell receptor diversity and heterologous immunity mediated by a cross-reactive T cell repertoire. Recently, mechanistic studies indicated that tissue-resident memory (Trm) cell populations including T cells, B cells and macrophages are already established in the fetus. Their role in human early life immunity, however, is not yet understood. Tissue-resident memory T cells, for example, are diminished in airway tissues in neonates as compared to older children or adults. Hence, the ability to make specific recall responses after secondary infectious stimulus is hampered, a phenomenon that is transcriptionally regulated by enhanced expression of T-bet. Furthermore, the microbiome establishment is a dominant factor to shape resident immunity at mucosal surfaces, but it is often disturbed in the context of preterm birth. The proposed function of Trm T cells to remember benign interactions with the microbiome might therefore be reduced which would contribute to an increased risk for sustained inflammation. An improved understanding of Trm interactions may determine novel targets of vaccination, e.g., modulation of T-bet responses and facilitate more individualized approaches to protect preterm babies in the future.},
  language  = {en}
}
@article{FischerDirksKlaussneretal.2022,
  author    = {Fischer, Jonas and Dirks, Johannes and Klaussner, Julia and Haase, Gabriele and Holl-Wieden, Annette and Hofmann, Christine and Hackenberg, Stephan and Girschick, Hermann and Morbach, Henner},
  title     = {Effect of clonally expanded PD-1\(^h\)\(^i\)\(^g\)\(^h\) CXCR5-CD4+ peripheral T Helper cells on B cell differentiation in the joints of patients with antinuclear antibody-positive juvenile idiopathic arthritis},
  series = {Arthritis \& Rheumatology},
  volume    = {74},
  journal   = {Arthritis \& Rheumatology},
  number    = {1},
  doi       = {10.1002/art.41913},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256607},
  pages     = {150-162},
  year      = {2022},
  abstract  = {Objective Antinuclear antibody (ANA)-positive juvenile idiopathic arthritis (JIA) is characterized by synovial B cell hyperactivity, but the precise role of CD4+ T cells in promoting local B cell activation is unknown. This study was undertaken to determine the phenotype and function of synovial CD4+ T cells that promote aberrant B cell activation in JIA. Methods Flow cytometry was performed to compare the phenotype and cytokine patterns of PD-1\(^h\)\(^i\)\(^g\)\(^h\)CD4+ T cells in the synovial fluid (SF) of patients with JIA and T follicular helper cells in the tonsils of control individuals. TCRVB next-generation sequencing was used to analyze T cell subsets for signs of clonal expansion. The functional impact of these T cell subsets on B cells was examined in cocultures in vitro. Results Multidimensional flow cytometry revealed the expansion of interleukin-21 (IL-21) and interferon-γ (IFNγ)-coexpressing PD-1\(^h\)\(^i\)\(^g\)\(^h\)CXCR5-HLA-DR+CD4+ T cells that accumulate in the joints of ANA-positive JIA patients. These T cells exhibited signs of clonal expansion with restricted T cell receptor clonotypes. The phenotype resembled peripheral T helper (Tph) cells with an extrafollicular chemokine receptor pattern and high T-bet and B lymphocyte-induced maturation protein 1 expression, but low B cell lymphoma 6 expression. SF Tph cells, by provision of IL-21 and IFNy, skewed B cell differentiation toward a CD21\(^l\)\(^o\)\(^w\)\(^/\)\(^-\)CD11c+ phenotype in vitro. Additionally, SF Tph cell frequencies correlated with the appearance of SF CD21\(^l\)\(^o\)\(^w\)\(^/\)\(^-\)CD11c+CD27-IgM- double-negative (DN) B cells in situ.},
  language  = {en}
}
@article{DirksFischerHaaseetal.2021,
  author    = {Dirks, Johannes and Fischer, Jonas and Haase, Gabriele and Holl-Wieden, Annette and Hofmann, Christine and Girschick, Hermann and Morbach, Henner},
  title     = {CD21\(^{lo/-}\)CD27\(^-\)IgM\(^-\) Double-Negative B Cells Accumulate in the Joints of Patients With Antinuclear Antibody-Positive Juvenile Idiopathic Arthritis},
  series = {Frontiers in Pediatrics},
  volume    = {9},
  journal   = {Frontiers in Pediatrics},
  issn      = {2296-2360},
  doi       = {10.3389/fped.2021.635815},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-236286},
  year      = {2021},
  abstract  = {Juvenile idiopathic arthritis (JIA) encompasses a heterogeneous group of diseases. The appearance of antinuclear antibodies (ANAs) in almost half of the patients suggests B cell dysregulation as a distinct pathomechanism in these patients. Additionally, ANAs were considered potential biomarkers encompassing a clinically homogenous subgroup of JIA patients. However, in ANA+ JIA patients, the site of dysregulated B cell activation as well as the B cell subsets involved in this process is still unknown. Hence, in this cross-sectional study, we aimed in an explorative approach at characterizing potential divergences in B cell differentiation in ANA+ JIA patients by assessing the distribution of peripheral blood (PB) and synovial fluid (SF) B cell subpopulations using flow cytometry. The frequency of transitional as well as switched-memory B cells was higher in PB of JIA patients than in healthy controls. There were no differences in the distribution of B cell subsets between ANA- and ANA+ patients in PB. However, the composition of SF B cells was different between ANA- and ANA+ patients with increased frequencies of CD21\(^{lo/-}\)CD27\(^-\)IgM\(^-\) "double negative" (DN) B cells in the latter. DN B cells might be a characteristic subset expanding in the joints of ANA+ JIA patients and are potentially involved in the antinuclear immune response in these patients. The results of our explorative study might foster further research dissecting the pathogenesis of ANA+ JIA patients.},
  language  = {en}
}