IgD/FcδR is involved in T-cell acute lymphoblastic leukemia and regulated by IgD-Fc-Ig fusion protein.

T-cell acute lymphoblastic leukemia (T-ALL) has a poor prognosis as a result of severe immunosuppression and rapid tumor progression with resistance to conventional chemotherapy. Excessive IgD may play a role in T cell activation via IgD Fc receptor (FcδR). Here we aimed to investigate the effects of IgD in T-ALL and demonstrated the potential benefit by targeting IgD/FcδR in T-ALL patients with IgD-Fc-Ig fusion protein. In T-ALL patients' blood samples and cell lines, the level of IgD, the percentage of FcδR expressing cells and the binding affinity were determined by flow cytometry. T cell viability, proliferation and apoptosis were analyzed. A mouse xenograft model was used to evaluate the in vivo effect of IgD-Fc-Ig, an IgD-FcδR blocker. The levels of serum IgD and FcδR were abnormally increased in part of T-ALL patients and IgD could induce over-proliferation and inhibit apoptosis of T-ALL cells in vitro. FcδR was constitutively expressed on T-ALL cells. IgD-Fc-Ig showed similar binding affinity to FcδR and selectively blocked the stimulation effect of IgD on T-ALL cells in vitro. In vivo study exhibited that IgD-Fc-Ig may also have therapeutic benefit. IgD-Fc-Ig administration inhibited human T-ALL growth and extended survival in xenograft T-ALL mice. In conclusion, this work supports the idea of targeting IgD/FcδR in T-ALL patients with excessive IgD. IgD-Fc-Ig fusion protein might be a potential biological drug with high selectivity for T-ALL treatment.

Clinical characteristics and outcomes of IgD myeloma: experience across UK national trials.

Immunoglobulin D (IgD) myeloma is a subtype often considered to have adverse features and inferior survival, but there is a paucity of data from large clinical studies. We compare the clinical characteristics and outcomes of patients with IgD myeloma from UK phase 3 myeloma trials analyzed in 2 groups: old (1980-2002) and recent (2002-2016) clinical trials, based on the time of adoption of novel myeloma therapies. Patients with IgD myeloma comprised 44 of 2789 (1.6%) and 70 of 5773 (1.2%) of the old and recent trials, respectively. Overall, IgD myeloma was associated with male predominance, low-level paraproteinemia (<10g/L), and λ light chain preference. The frequency of ultra-high-risk cytogenetics was similar in IgD myeloma compared with other subtypes (4.3% vs 5.3%, P > .99). Despite the old trial series being a younger group (median age: 59 vs 63 years, P = .015), there was a higher frequency of bone lesions, advanced stage at diagnosis, worse performance status, and severe renal impairment compared with the recent trials. Furthermore, the early mortality rate was significantly higher for the old trial series (20% vs 4%, P = .01). The overall response rate following induction therapy was significantly higher in the recent trials (89% vs 43%, P < .0001), and this was consistent with improved median overall survival (48 months; 95% confidence interval [CI] 35-67 months vs 22 months; 95% CI, 16-29 months). Survival outcomes for IgD myeloma have significantly improved and are now comparable to other myeloma types because of earlier diagnosis, novel therapies, and improved supportive care. This trial was registered at clinicaltrials.gov as # NCT01554852.

Primary Immune Responses and Affinity Maturation Are Controlled by IgD.

Mature B cells co-express IgM and IgD B cell antigen receptors (BCR) on their surface. While IgM BCR expression is already essential at early stages of development, the role of the IgD-class BCR remains unclear as most B cell functions appeared unchanged in IgD-deficient mice. Here, we show that IgD-deficient mice have an accelerated rate of B cell responsiveness as they activate antibody production within 24h after immunization, whereas wildtype (WT) animals required 3 days to activate primary antibody responses. Strikingly, soluble monovalent antigen suppresses IgG antibody production induced by multivalent antigen in WT mice. In contrast, IgD-deficient mice were not able to modulate IgG responses suggesting that IgD controls the activation rate of B cells and subsequent antibody production by sensing and distinguishing antigen-valences. Using an insulin-derived peptide we tested the role of IgD in autoimmunity. We show that primary autoreactive antibody responses are generated in WT and in IgD-deficient mice. However, insulin-specific autoantibodies were detected earlier and caused more severe symptoms of autoimmune diabetes in IgD-deficient mice as compared to WT mice. The rapid control of autoimmune diabetes in WT animals was associated with the generation of high-affinity IgM that protects insulin from autoimmune degradation. In IgD-deficient mice, however, the generation of high-affinity protective IgM is delayed resulting in prolonged autoimmune diabetes. Our data suggest that IgD is required for the transition from primary, highly autoreactive, to secondary antigen-specific antibody responses generated by affinity maturation.

Immunoglobulin D and cardiac amyloidosis: development and a case illustration.

Amyloidosis results from extra-cellular deposition of proteins which interfere with tissue function. We report the case of a patient with pathological heart involvement which is caused by immunoglobulin D amyloidosis, and review current data on the amyloidois diagnosis and management.

Bacterial exploitation of phosphorylcholine mimicry suppresses inflammation to promote airway infection.

Regulation of neutrophil activity is critical for immune evasion among extracellular pathogens, yet the mechanisms by which many bacteria disrupt phagocyte function remain unclear. Here, we have shown that the respiratory pathogen Streptococcus pneumoniae disables neutrophils by exploiting molecular mimicry to degrade platelet-activating factor (PAF), a host-derived inflammatory phospholipid. Using mass spectrometry and murine upper airway infection models, we demonstrated that phosphorylcholine (ChoP) moieties that are shared by PAF and the bacterial cell wall allow S. pneumoniae to leverage a ChoP-remodeling enzyme (Pce) to remove PAF from the airway. S. pneumoniae-mediated PAF deprivation impaired viability, activation, and bactericidal capacity among responding neutrophils. In the absence of Pce, neutrophils rapidly cleared S. pneumoniae from the airway and impeded invasive disease and transmission between mice. Abrogation of PAF signaling rendered Pce dispensable for S. pneumoniae persistence, reinforcing that this enzyme deprives neutrophils of essential PAF-mediated stimulation. Accordingly, exogenous activation of neutrophils overwhelmed Pce-mediated phagocyte disruption. Haemophilus influenzae also uses an enzyme, GlpQ, to hydrolyze ChoP and subvert PAF function, suggesting that mimicry-driven immune evasion is a common paradigm among respiratory pathogens. These results identify a mechanism by which shared molecular structures enable microbial enzymes to subvert host lipid signaling, suppress inflammation, and ensure bacterial persistence at the mucosa.

Current advances in the understanding and treatment of mevalonate kinase deficiency.

Mevalonate kinase deficiency (MKD) is a rare autosomal recessive autoinflammatory metabolic disease that is caused by mutations in the MVK gene. Patients with MKD typically have an early onset in infancy. MKD is characterized by recurrent episodes of high fever, abdominal distress, diffuse joint pain, and skin rashes. In a subset of patients, MKD is also associated with elevated serum immunoglobulin D (IgD) levels (hyperimmunoglobulinemia D syndrome, HIDS). The clinical phenotype of MKD varies widely and depends on the severity of the impaired mevalonate kinase activity. Complete impairment results in the severe metabolic disease, mevalonic aciduria, while a partial deficiency results in a broad spectrum of clinical presentation, including HIDS. The precise molecular mechanisms behind the elevated serum IgD levels and inflammation that occurs in MKD remain unknown. Children who exhibit symptoms of MKD should be tested for mutations in the MKD gene. However, the complexity of MKD often results in delays in its definitive diagnosis and the outcome in adult age is not completely known. Therapeutic options for MKD are based on limited data and include non-steroidal anti-inflammatory drugs, corticosteroids, and biological agents that target specific cytokine pathways. In recent years, some studies have reported promising results for new biological drugs; however, these cases have failed to achieve satisfactory remission. Therefore, further studies are needed to understand the pathogenesis of MKD and identify innovative therapeutic tools for its management.

Abrogation of nontypeable Haemophilus influenzae protein D function reduces phosphorylcholine decoration, adherence to airway epithelial cells, and fitness in a chinchilla model of otitis media.

The pneumococcal polysaccharide conjugate vaccine which includes a nonacylated protein D carrier from Haemophilus influenzae has been recently licensed for use in many countries. While this vaccine is protective against nontypeable Haemophilus influenzae (NTHI)-induced acute otitis media (OM), the mechanism underlying this protective efficacy is not yet fully understood. Protein D/glycerophosphodiester phosphodiesterase (PD/GlpQ) is an outer membrane lipoprotein expressed by NTHI that has been ascribed several functions, including host cell adherence and phosphorylcholine (PCho) acquisition. We found that a pd/glpQ NTHI mutant exhibited reduced adherence to airway epithelial cells, diminished phosphorylcholine (PCho) decoration of biofilms, and compromised fitness during experimental acute OM compared to the parent strain. We also found that exposure of NTHI to antibodies directed against the vaccine formulation recapitulated the PCho decoration and NTHI adherence phenotypes exhibited by PD/GlpQ-deficient NTHI, providing at least two likely mechanisms by which the pneumococcal polysaccharide-PD/GlpQ conjugate vaccine induces protection from NTHI-induced OM.

Neisseria lactamica selectively induces mitogenic proliferation of the naive B cell pool via cell surface Ig.

Neisseria lactamica is a commensal bacteria that colonizes the human upper respiratory tract mucosa during early childhood. In contrast to the closely related opportunistic pathogen Neisseria meningitidis, there is an absence of adaptive cell-mediated immunity to N. lactamica during the peak age of carriage. Instead, outer membrane vesicles derived from N. lactamica mediate a B cell-dependent proliferative response in mucosal mononuclear cells that is associated with the production of polyclonal IgM. We demonstrate in this study that this is a mitogenic human B cell response that occurs independently of T cell help and any other accessory cell population. The ability to drive B cell proliferation is a highly conserved property and is present in N. lactamica strains derived from diverse clonal complexes. CFSE staining of purified human tonsillar B cells demonstrated that naive IgD(+) and CD27(-) B cells are selectively induced to proliferate by outer membrane vesicles, including the innate CD5(+) subset. Neither purified lipooligosaccharide nor PorB from N. lactamica is likely to be responsible for this activity. Prior treatment of B cells with pronase to remove cell-surface Ig or treatment with BCR-specific Abs abrogated the proliferative response to N. lactamica outer membrane vesicles, suggesting that this mitogenic response is dependent upon the BCR.

CD20 deficiency in humans results in impaired T cell-independent antibody responses.

CD20 was the first B cell differentiation antigen identified, and CD20-specific mAbs are commonly used for the treatment of B cell malignancies and autoantibody-mediated autoimmune diseases. Despite this the role of CD20 in human B cell physiology has remained elusive. We describe here a juvenile patient with CD20 deficiency due to a homozygous mutation in a splice junction of the CD20 gene (also known as MS4A1) that results in "cryptic" splicing and nonfunctional mRNA species. Analysis of this patient has led us to conclude that CD20 has a central role in the generation of T cell-independent (TI) antibody responses. Key evidence to support this conclusion was provided by the observation that although antigen-independent B cells developed normally in the absence of CD20 expression, antibody formation, particularly after vaccination with TI antigens, was strongly impaired in the patient. Consistent with this, TI antipolysaccharide B cell responses were severely impeded in CD20-deficient mice. Our study therefore identifies what we believe to be a novel type of humoral immunodeficiency caused by CD20 deficiency and characterized by normal development of antigen-independent B cells, along with a reduced capacity to mount proper antibody responses.

Functional maturation of the human antibody response to rotavirus.

Infant Abs induced by viruses exhibit poor functional activity compared with those of adults. The human B cell response to rotavirus is dominated by use of the V(H)1-46 gene segment in both adults and infants, but only adult sequences are highly mutated. We investigated in detail the kinetic, structural, and functional advantage conferred by individual naturally occurring somatic mutations in rotavirus-specific human Abs encoded by the immunodominant V(H)1-46 gene segment. Adult Abs achieved enhanced binding through naturally occurring somatic mutations in the H chain CDR2 region that conferred a markedly prolonged off-rate and a desirable increase in antiviral potency. Three-dimensional cryoelectron microscopy studies of Ag-Ab complexes revealed the mechanism of viral inhibition to be the binding of high-affinity Abs at the viral RNA release pore in the double-layer particle. These structure-function studies suggest a molecular basis for the poor quality of Abs made in infancy following virus infection or immunization.

Moraxella catarrhalis-dependent tonsillar B cell activation does not lead to apoptosis but to vigorous proliferation resulting in nonspecific IgM production.

The respiratory pathogen Moraxella catarrhalis has a high affinity for human IgD and is mitogenic for peripheral blood B lymphocytes. Moraxella IgD-binding protein, which is a multifunctional outer membrane protein with adhesive properties, is responsible for the interaction. Previous experiments with the Ig-binding B cell superantigens protein A and protein L from Staphylococcus aureus and Peptostreptococcus magnus, respectively, have suggested that nonimmune BCR cross-linking induces B cell apoptosis through the intrinsic pathway. The goal of this study was to characterize early and late B cell events in the presence of M. catarrhalis in comparison with S. aureus. Despite an increased phosphatidyl serine translocation as revealed by Annexin V binding in flow cytometry analyses, neither M. catarrhalis nor S. aureus induced activation-associated apoptotic cell death in purified human tonsillar B cells. In contrast, a vigorous B cell proliferation, as quantified using thymidine incorporation and CFSE staining, was observed. An increased expression of an array of surface proteins (i.e., CD19, CD21, CD40, CD45, CD54, CD69, CD86, CD95, and HLA-DR) and IgM production was found upon activation with M. catarrhalis. In conclusion, M. catarrhalis-dependent B cell activation does not result in apoptosis but in cell division and nonspecific IgM synthesis, suggesting that the bacterial interaction with tonsillar B cells serves to redirect the early adaptive immune response.

IgM-mediated signaling is required for the development of a normal B cell memory response.

Mature B cells co-express both IgM and IgD types of antigen receptors before activation. Our earlier work has shown that the co-expression of IgD and IgM plays an important role in regulating the composition of antibody repertoire during a primary immune response. However, the roles of these two B cell receptors in the development of B cell memory responses remain unclear. The present study shows that during the secondary immune response to (4-hydroxy-3-nitrophenyl)acetyl (NP), IgM-/- mice secreted significant amount of NP-specific IgD antibodies. The kinetics of antigen-specific IgD antibodies produced in IgM-/- mice was similar to that of IgM antibodies in wild type mice during the secondary response. However, the production of antigen-specific class-switched antibodies in IgM-/- mice was significantly reduced compared to that in wild type mice, particularly at the early phase of the memory response. In addition, germinal center (GC) reaction was significantly diminished in IgM-/- mice after secondary challenge with soluble antigen. Nevertheless, affinity maturation of antibodies appears largely intact in IgM-/- mice during memory response. Thus, our studies demonstrate that IgM-mediated signaling plays an important role in the development of efficient B cell memory responses.

Identification of IgF, a hinge-region-containing Ig class, and IgD in Xenopus tropicalis.

Only three Ig isotypes, IgM, IgX, and IgY, were previously known in amphibians. Here, we describe a heavy-chain isotype in Xenopus tropicalis, IgF (encoded by C(phi)), with only two constant region domains. IgF is similar to amphibian IgY in sequence, but the gene contains a hinge exon, making it the earliest example, in evolution, of an Ig isotype with a separately encoded genetic hinge. We also characterized a gene for the heavy chain of IgD, located immediately 3' of C(mu), that shares features with the C(delta) gene in fish and mammals. The latter gene contains eight constant-region-encoding exons and, unlike the chimeric splicing of muC(H)1 onto the IgD heavy chain in teleost fish, it is expressed as a unique IgD heavy chain. The IgH locus of X. tropicalis shows a 5' V(H)-D(H)-J(H)-C(mu)-C(delta)-C(chi)-C(upsilon)-C(phi) 3' organization, suggesting that the mammalian and amphibian Ig heavy-chain loci share a common ancestor.

The riddle of the dual expression of IgM and IgD.

Signalling through the B cell antigen receptor (BCR) is required for peripheral B lymphocyte maturation, maintenance, activation and silencing. In mature B cells, the antigen receptor normally consists of two isotypes, membrane IgM and IgD (mIgM, mIgD). Although the signals initiated from both isotypes differ in kinetics and intensity, in vivo, the BCR of either isotype seems to be able to compensate for the loss of the other, reflected by the mild phenotypes of mice deficient for mIgM or mIgD. Thus, it is still unclear why mature B cells need expression of mIgD in addition to mIgM. In the current review we suggest that the view that IgD has a simply definable function centred around the basic signalling function should be replaced by the assumption that IgD fine tunes humoral responses, modulates B cell selection and homeostasis and thus shapes the B cell repertoire, defining IgD to be a key modulator of the humoral immune response.

IgD, like IgM, is a primordial immunoglobulin class perpetuated in most jawed vertebrates.

IgD has remained a mysterious Ig class and a bane to immunology students since its discovery >40 years ago. Its spotty occurrence in mammals and birds and the discovery of an isotype with similarities to IgD in bony fish are perplexing. We have identified IgD heavy (H) chain (delta) from the amphibian Xenopus tropicalis during examination of the IgH locus. The Xenopus delta gene is in the same position, immediately 3' of the IgM gene, as in mammals, and it is expressed only in the spleen at low levels, primarily as a transmembrane receptor by surface IgM(+) cells. Our data suggest that frog IgD is expressed on mature B cells, like in mouse/human. Unexpectedly, Xenopus IgD is orthologous to IgW, an Ig isotype found only in cartilaginous fish and lungfish, demonstrating that IgD/W, like IgM, was present in the ancestor of all living jawed vertebrates. In striking contrast to IgM, IgD/W is evolutionarily labile, showing many duplications/deletions of domains, the presence of multiple splice forms, existence as predominantly a secretory or transmembrane form, or loss of the entire gene in a species-specific manner. Our study suggests that IgD/W has played varied roles in different vertebrate taxa since the inception of the adaptive immune system, and it may have been preserved as a flexible locus over evolutionary time to complement steadfast IgM.

K+ channel expression during B cell differentiation: implications for immunomodulation and autoimmunity.

Using whole-cell patch-clamp, fluorescence microscopy and flow cytometry, we demonstrate a switch in potassium channel expression during differentiation of human B cells from naive to memory cells. Naive and IgD(+)CD27(+) memory B cells express small numbers of the voltage-gated Kv1.3 and the Ca(2+)-activated intermediate-conductance IKCa1 channel when quiescent, and increase IKCa1 expression 45-fold upon activation with no change in Kv1.3 levels. In contrast, quiescent class-switched memory B cells express high levels of Kv1.3 ( approximately 2000 channels/cell) and maintain their Kv1.3(high) expression after activation. Consistent with their channel phenotypes, proliferation of naive and IgD(+)CD27(+) memory B cells is suppressed by the specific IKCa1 inhibitor TRAM-34 but not by the potent Kv1.3 blocker Stichodactyla helianthus toxin, whereas the proliferation of class-switched memory B cells is suppressed by Stichodactyla helianthus toxin but not TRAM-34. These changes parallel those reported for T cells. Therefore, specific Kv1.3 and IKCa1 inhibitors may have use in therapeutic manipulation of selective lymphocyte subsets in immunological disorders.

IgD+IgM- B cells mount immune responses that exhibit altered antibody repertoire.

IgM and IgD expression during B cell development and differentiation is strictly and developmentally controlled. Although studies have suggested subtle differences in B cell activation, tolerance, and affinity maturation when antigens ligate cell membrane IgM or IgD, the mechanisms that may explain these differences remain unknown and no drastic differences in immune responses have been reported in mice whose B cells selectively lack IgM or IgD. We now show that the antibody repertoire in IgM(-/-) mice is dramatically altered during the primary response to phosphorylcholine. In IgM(-/-) mice, B cells that are activated and differentiate into antibody-forming cells and germinal center B cells express VH genes other than the T15 genes that dominate in wild-type mice. The kinetics of the antigen-specific IgD primary antibody response in IgM(-/-) mice appears similar to that of IgG, but not to that of IgM in wild-type mice. Thus, our studies demonstrate that differences in the roles played by IgM and IgD in regulating the responsiveness and differentiation of B lymphocytes can have major biological consequences during adaptive immune responses.

BCR mutants deficient in ligand-independent and more sensitive for ligand-dependent signaling.

Signal transduction by the B cell antigen receptor (BCR) regulates development, survival and clonal expansion of B cells. The BCR complex comprises the membrane-bound immunoglobulin molecule (mIg) and the Ig-alpha/Ig-beta heterodimer, and was shown to form oligomeric structures. In pervanadate (PV)-treated B cells, multiple proteins are tyrosine phosphorylated upon expression of the BCR, indicating that the BCR can signal in an antigen-independent fashion. We analyzed the signal transduction from BCR mutants which either have an altered heavy chain transmembrane region or lack the Ig-alpha cytoplasmic tail. In comparison to cells expressing the wild-type receptors, those with a mutant BCR respond to PV treatment with reduced and retarded tyrosine phosphorylation of substrate proteins. Conversely, the cells with mutant BCR are more sensitive to stimulation with low doses of antigen. These data suggest that a correctly assembled BCR complex is important for antigen-independent signaling and setting the threshold for antigen-dependent BCR activation.