Antibody responses against bacterial glycans affinity mature and diversify in germinal centers.

Anti-carbohydrate antibodies (Abs) play crucial roles in pathogen control, but their generation remains poorly understood. By studying responses to in humans, we reveal that the glycan-targeted response shifts from IgM towards IgG and IgA memory with age and antigen exposure across blood, spleen, and tonsils. Both natural colonization and controlled human infection with increased class-switched B cells, with evidence of within-clone switching.

Syndecans and glycosaminoglycans influence B-cell development and activation.

Syndecans (SDCs) are glycosaminoglycan-containing cell surface proteins with diverse functions in the immune system with SDC1 (CD138) and SDC4 expressed in B-lineage cells. Here, we show that stem cells lacking either molecule generate fewer B-cell progenitors but give rise to mature B cells in vivo. Deletion of the plasma cell "marker" CD138 has no effect on homeostatic or antigen-induced plasma cell formation.

Single-Cell Transcriptomics Identifies a Prominent Role for the MIF-CD74 Axis in Myasthenia Gravis Thymus.

Background And Objectives: Myasthenia gravis (MG) is an autoimmune disease most frequently caused by autoantibodies (auto-Abs) against the acetylcholine receptor (AChR) located at the neuromuscular junction. Thymic follicular hyperplasia is present in most of the patients with early-onset AChR-Ab MG (EOMG), but its cellular and molecular drivers and development remain poorly understood.

Methods: We constructed a single cell-based transcriptional profile of lymphoid cell types in thymi from 11 immunotherapy-naïve patients with EOMG.

Conversion of vaccines from low to high immunogenicity by antibodies with epitope complementarity.

Existing antibodies (Abs) have varied effects on humoral immunity during subsequent infections. Here, we leveraged in vivo systems that allow precise control of antigen-specific Abs and B cells to examine the impact of Ab dose, affinity, and specificity in directing B cell activation and differentiation. Abs competing with the B cell receptor (BCR) epitope showed affinity-dependent suppression.

B Cell Receptor Transgenic Mice as Tools to Study Memory B Cells.

B cell receptor (BCR) transgenic mice allow the control of the initial target (antigen) specificity of naïve B cells and to investigate their properties following activation. Here, I describe how BCR transgenic B cells can be used in combination with adoptive cell transfer and immunization models to study memory B cell formation and reactivation.

Ki67 deficiency impedes chromatin accessibility and BCR gene rearrangement.

The proliferation marker Ki67 has been attributed critical functions in maintaining mitotic chromosome morphology and heterochromatin organization during the cell cycle, indicating a potential role in developmental processes requiring rigid cell-cycle control. Here, we discovered that despite normal fecundity and organogenesis, germline deficiency in Ki67 resulted in substantial defects specifically in peripheral B and T lymphocytes. This was not due to impaired cell proliferation but rather to early lymphopoiesis at specific stages where antigen-receptor gene rearrangements occurred.

Intrinsically determined turnover underlies broad heterogeneity in plasma-cell lifespan.

Antibodies produced by antibody-secreting plasma cells (ASCs) underlie multiple forms of long-lasting immunity. Here we examined the mechanisms regulating ASC turnover and persistence using a genetic reporter to time-stamp ASCs. This approach revealed ASC lifespans as heterogeneous and falling on a continuum, with only a small fraction surviving for >60 days.

Long-lived plasma cells accumulate in the bone marrow at a constant rate from early in an immune response.

Vaccines work largely by generating long-lived plasma cells (LLPCs), but knowledge of how such cells are recruited is sparse. Although it is clear that LLPCs preferentially originate in germinal centers (GCs) and relocate to survival niches in bone marrow where they can persist for decades, the issues of the timing of LLPC recruitment and the basis of their retention remain uncertain. Here, using a genetic timestamping system in mice, we show that persistent PCs accrue in bone marrow at an approximately constant rate of one cell per hour over a period spanning several weeks after a single immunization with a model antigen.

Time is of the essence for vaccine success.

Effective vaccines elicit neutralizing antibodies and long-lasting memory, but this can be challenging with some pathogens, such as HIV. A new study shows how a slow-delivery protein immunization strategy administered in dose-escalation format over 12 days increased the durability of germinal centers and improved immunological outcomes.

Interleukin-21, acting beyond the immunological synapse, independently controls T follicular helper and germinal center B cells.

Germinal centers (GCs), transient structures within B cell follicles and central to affinity maturation, require the coordinated behavior of T and B cells. IL-21, a pleiotropic T cell-derived cytokine, is key to GC biology through incompletely understood mechanisms. By genetically restricting production and receipt of IL-21 in vivo, we reveal how its independent actions on T and B cells combine to regulate the GC.

IL-21 has a critical role in establishing germinal centers by amplifying early B cell proliferation.

The proliferation and differentiation of antigen-specific B cells, including the generation of germinal centers (GC), are prerequisites for long-lasting, antibody-mediated immune protection. Affinity for antigen determines B cell recruitment, proliferation, differentiation, and competitiveness in the response, largely through determining access to T cell help. However, how T cell-derived signals contribute to these outcomes is incompletely understood.

The concerted change in the distribution of cell cycle phases and zone composition in germinal centers is regulated by IL-21.

Humoral immune responses require germinal centres (GC) for antibody affinity maturation. Within GC, B cell proliferation and mutation are segregated from affinity-based positive selection in the dark zone (DZ) and light zone (LZ) substructures, respectively. While IL-21 is known to be important in affinity maturation and GC maintenance, here we show it is required for both establishing normal zone representation and preventing the accumulation of cells in the G1 cell cycle stage in the GC LZ.

B cell memory: understanding COVID-19.

Immunological memory is a mechanism to protect us against reinfection. Antibodies produced by B cells are integral to this defense strategy and underlie virtually all vaccine success. Here, we explain how B cells memory is generated by infection and vaccination, what influences its efficacy and its persistence, and how characterizing these parameters in the immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will help achieve protective immunity through vaccination.

EBV renders B cells susceptible to HIV-1 in humanized mice.

HIV and EBV are human pathogens that cause a considerable burden to worldwide health. In combination, these viruses are linked to AIDS-associated lymphomas. We found that EBV, which transforms B cells, renders them susceptible to HIV-1 infection in a CXCR4 and CD4-dependent manner in vitro and that CXCR4-tropic HIV-1 integrates into the genome of these B cells with the same molecular profile as in autologous CD4 T cells.

The Amount of BCL6 in B Cells Shortly after Antigen Engagement Determines Their Representation in Subsequent Germinal Centers.

It is unknown whether the incremental increases in BCL6 amounts in antigen-activated B cells influence the unfolding differentiation before germinal center (GC) formation. By comparing shortly after immunization the distribution of conventional B cells to those enforced to express BCL6 at the upper quartile of normal and those lacking BCL6 altogether, we determined that B cell representation in the stages before the GC compartment was related to BCL6 amounts. This was not by increased proliferation or suppression of early plasmablast differentiation, but rather by preferential recruitment and progression through these early stages of B cell activation, culminating in preferential transition into GC.

IVIG efficacy in CIDP patients is not associated with terminal complement inhibition.

Patients with acute and chronic inflammatory demyelinating neuropathies exhibit elevated serum and cerebrospinal fluid (CSF) levels of terminal complement activation products and therapeutic inhibition of complement activation is currently tested for its safety and efficacy in patients with Guillain-Barré syndrome (GBS). Here, we determined serum levels of the complement activation products C3a, C5a and the soluble terminal complement complex (sTCC) in 39 individuals with chronic inflammatory demyelinating polyneuropathy (CIDP) who participated in one of the largest ever conducted clinical trial in patients with CIDP (ICE trial) and received Intravenous Immunoglobulin (IVIG) or placebo (albumin) in 3 week intervals for up to 24 weeks. In placebo-treated patients with spontaneous disease remission, serum sTCC levels moderately decreased over time.

Interleukins 12 and 15 induce cytotoxicity and early NK-cell differentiation in type 3 innate lymphoid cells.

Type 3 innate lymphoid cells (ILC3s) fulfill protective functions at mucosal surfaces via cytokine production. Although their plasticity to become ILC1s, the innate counterparts of type 1 helper T cells, has been described previously, we report that they can differentiate into cytotoxic lymphocytes with many characteristics of early differentiated natural killer (NK) cells. This transition is promoted by the proinflammatory cytokines interleukin 12 (IL-12) and IL-15, and correlates with expression of the master transcription factor of cytotoxicity, eomesodermin (Eomes).

ATG-dependent phagocytosis in dendritic cells drives myelin-specific CD4 T cell pathogenicity during CNS inflammation.

Although reactivation and accumulation of autoreactive CD4 T cells within the CNS are considered to play a key role in the pathogenesis of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), the mechanisms of how these cells recognize their target organ and induce sustained inflammation are incompletely understood. Here, we report that mice with conditional deletion of the essential autophagy protein ATG5 in classical dendritic cells (DCs), which are present at low frequencies in the nondiseased CNS, are completely resistant to EAE development following adoptive transfer of myelin-specific T cells and show substantially reduced in situ CD4 T cell accumulation during the effector phase of the disease. Endogenous myelin peptide presentation to CD4 T cells following phagocytosis of injured, phosphatidylserine-exposing oligodendroglial cells is abrogated in the absence of ATG5.

Persistent KSHV Infection Increases EBV-Associated Tumor Formation In Vivo via Enhanced EBV Lytic Gene Expression.

The human tumor viruses Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) establish persistent infections in B cells. KSHV is linked to primary effusion lymphoma (PEL), and 90% of PELs also contain EBV. Studies on persistent KSHV infection in vivo and the role of EBV co-infection in PEL development have been hampered by the absence of small animal models.

Fc-Galactosylation of Human Immunoglobulin Gamma Isotypes Improves C1q Binding and Enhances Complement-Dependent Cytotoxicity.

Binding of the complement component C1q to the CH2 domain of antigen-bound immunoglobulin gamma (IgG) activates the classical complement pathway and depends on its close proximity to Fc fragments of neighboring antibodies. IgG subclasses contain a highly conserved asparagine 297 (N)-linked biantennary glycan within their CH2 domains, the core structure of which can be extended with terminal galactose and sialic acid residues. To investigate whether Fc-glycosylation regulates effector functions of human IgG subclasses, we cloned the antigen-binding region of the CD20-specific monoclonal antibody rituximab into IgG isotype expression vectors.

IVIG regulates the survival of human but not mouse neutrophils.

Intravenous immunoglobulin (IVIG) are purified IgG preparations made from the pooled plasma from thousands of healthy donors and are being tested in preclinical mouse models. Inherent challenges, however, are the pluripotency of IVIG and its xenogeneicity in animals. IVIG can alter the viability of human neutrophils via agonistic antibodies to Fas and Siglec-9.

The autophagy machinery restrains iNKT cell activation through CD1D1 internalization.

Invariant natural killer T (iNKT) cells are innate T cells with powerful immune regulatory functions that recognize glycolipid antigens presented by the CD1D protein. While iNKT cell-activating glycolipids are currently being explored for their efficacy to improve immunotherapy against infectious diseases and cancer, little is known about the mechanisms that control CD1D antigen presentation and iNKT cell activation in vivo. CD1D molecules survey endocytic pathways to bind lipid antigens in MHC class II-containing compartments (MIICs) before recycling to the plasma membrane.

Terminal complement activation is increased and associated with disease severity in CIDP.

Chronic inflammatory demyelinating polyneuropathy (CIDP) is the most common chronic autoimmune neuropathy. While both cell-mediated and humoral mechanisms contribute to its pathogenesis, the rapid clinical response to plasmapheresis implicates a circulating factor responsible for peripheral nerve injury. We report that treatment-naïve patients with CIDP show increased serum and CSF levels of the anaphylatoxin C5a and the soluble terminal complement complex (sTCC).