CD40 ligand/CD40 deficiency

Beyond monogenetic rare variants: tackling the low rate of genetic diagnoses in predominantly antibody deficiency

Predominantly antibody deficiency (PAD) is the most prevalent form of primary immunodeficiency, and is characterized by broad clinical, immunological and genetic heterogeneity. Utilizing the current gold standard of whole exome sequencing for diagnosis, pathogenic gene variants are only identified in less than 20% of patients. While elucidation of the causal genes underlying PAD has provided many insights into the cellular and molecular mechanisms underpinning disease pathogenesis, many other genes may remain as yet undefined to enable definitive diagnosis, prognostic monitoring and targeted therapy of patients. Considering that many patients display a relatively late onset of disease presentation in their 2nd or 3rd decade of life, it is questionable whether a single genetic lesion underlies disease in all patients. Potentially, combined effects of other gene variants and/or non-genetic factors, including specific infections can drive disease presentation. In this review, we define (1) the clinical and immunological variability of PAD, (2) consider how genetic defects identified in PAD have given insight into B-cell immunobiology, (3) address recent technological advances in genomics and the challenges associated with identifying causal variants, and (4) discuss how functional validation of variants of unknown significance could potentially be translated into increased diagnostic rates, improved prognostic monitoring and personalized medicine for PAD patients. A multidisciplinary approach will be the key to curtailing the early mortality and high morbidity rates in this immune disorder.

Diversity of Immunoglobulin (Ig) Isotypes and the Role of Activation-Induced Cytidine Deaminase (AID) in Fish

The disparate diversity in immunoglobulin (Ig) repertoire has been a subject of fascination since the emergence of prototypic adaptive immune system in vertebrates. The carboxy terminus region of activation-induced cytidine deaminase (AID) has been well established in tetrapod lineage and is crucial for its function in class switch recombination (CSR) event of Ig diversification. The absence of CSR in the paraphyletic group of fish is probably due to changes in catalytic domain of AID and lack of cis-elements in IgH locus. Therefore, understanding the arrangement of Ig genes in IgH locus and functional facets of fish AID opens up new realms of unravelling the alternative mechanisms of isotype switching and antibody diversity. Further, the teleost AID has been recently reported to have potential of catalyzing CSR in mammalian B cells by complementing AID deficiency in them. In that context, the present review focuses on the recent advances regarding the generation of diversity in Ig repertoire in the absence of AID-regulated class switching in teleosts and the possible role of T cell-independent pathway involving B cell activating factor and a proliferation-inducing ligand in activation of CSR machinery.

Identification and characterization of CD40 from humphead snapper (Lutjanus sanguineus)

CD40 is known as "master switch" in immune response to pathogen infection in mammals. However, limited information of CD40 is known in lower vertebrates. In this study, a novel CD40 homolog (Ls-CD40) was cloned and characterized from humphead snapper, Lutjanus sanguineus. The Ls-CD40 cDNA composed of 2073 bp with a 69 bp of 5'-UTR, a 1020 bp of 3'-UTR and an open reading frame (ORF) of 984 bp, encoding 327 amino acid residues. Sequence analysis showed that Ls-CD40 contained a single peptide, a transmembrane domain and four cysteine-rich domains. The deduced amino acid sequence of Ls-CD40 shared 40%-53% identities with other known fish CD40. The qRT-PCR showed that Ls-CD40 gene expressed in all examined tissues with the most abundant in spleen and lowest level in intestine. After V. harveyi and poly I:C stimulation, the expression of CD40 were significantly induced in spleen. Moreover, Ls-CD40 could interact with Ls-TRAF3 in vitro. These data indicate that Ls-CD40 might play a regulatory role in immune response of L. sanguineus.

Simultaneous Subcutaneous and Intranasal Administration of a CAF01-Adjuvanted Chlamydia Vaccine Elicits Elevated IgA and Protective Th1/Th17 Responses in the Genital Tract

The selection of any specific immunization route is critical when defining future vaccine strategies against a genital infection like Chlamydia trachomatis (C.t.). An optimal Chlamydia vaccine needs to elicit mucosal immunity comprising both neutralizing IgA/IgG antibodies and strong Th1/Th17 responses. A strategic tool to modulate this immune profile and mucosal localization of vaccine responses is to combine parenteral and mucosal immunizations routes. In this study, we investigate whether this strategy can be adapted into a two-visit strategy by simultaneous subcutaneous (SC) and nasal immunization. Using a subunit vaccine composed of C.t. antigens (Ags) adjuvanted with CAF01, a Th1/Th17 promoting adjuvant, we comparatively evaluated Ag-specific B and T cell responses and efficacy in mice following SC and simultaneous SC and nasal immunization (SIM). We found similar peripheral responses with regard to interferon gamma and IL-17 producing Ag-specific splenocytes and IgG serum levels in both vaccine strategies but in addition, the SIM protocol also led to Ag-specific IgA responses and increased B and CD4⁺ T cells in the lung parenchyma, and in lower numbers also in the genital tract (GT). Following vaginal infection with C.t., we observed that SIM immunization gave rise to an early IgA response and IgA-secreting plasma cells in the GT in contrast to SC immunization, but we were not able to detect more rapid recruitment of mucosal T cells. Interestingly, although SIM vaccination in general improved mucosal immunity we observed no improved efficacy against genital infection compared to SC, a finding that warrants for further investigation. In conclusion, we demonstrate a novel vaccination strategy that combines systemic and mucosal immunity in a two-visit strategy.

Autoimmunity in primary T-cell immunodeficiencies

Primary immunodeficiency diseases (PID) are a genetically heterogeneous group of more than 270 disorders that affect distinct components of both humoral and cellular arms of the immune system. Primary T cell immunodeficiencies affect subjects at the early age of life. In most cases, T-cell PIDs become apparent as combined T- and B-cell deficiencies. Patients with T-cell PID are prone to life-threatening infections. On the other hand, non-infectious complications such as lymphoproliferative diseases, cancers and autoimmunity seem to be associated with the primary T-cell immunodeficiencies. Autoimmune disorders of all kinds (organ specific or systemic ones) could be subjected to this class of PIDs; however, the most frequent autoimmune disorders are immune thrombocytopenic purpura (ITP) and autoimmune hemolytic anemia (AIHA). In this review, we discuss the proposed mechanisms of autoimmunity and review the literature reported on autoimmune disorder in each type of primary T-cell immunodeficiencies.

CD40 agonist antibody mediated improvement of chronic Cryptosporidium infection in patients with X-linked hyper IgM syndrome

X-linked hyper-IgM syndrome (XHM) is a combined immune deficiency disorder caused by mutations in CD40 ligand. We tested CP-870,893, a human CD40 agonist monoclonal antibody, in the treatment of two XHM patients with biliary Cryptosporidiosis. CP-870,893 activated B cells and APCs in vitro, restoring class switch recombination in XHM B cells and inducing cytokine secretion by monocytes. CP-870,893 infusions were well tolerated and showed significant activity in vivo, decreasing leukocyte concentration in peripheral blood. Although specific antibody responses were lacking, frequent dosing in one subject primed T cells to secrete IFN-g and suppressed oocyst shedding in the stool. Nevertheless, relapse occurred after discontinuation of therapy. The CD40 receptor was rapidly internalized following binding with CP-870,893, potentially explaining the limited capacity of CP-870,893 to mediate immune reconstitution. This study demonstrates that CP-870,893 suppressed oocysts shedding in XHM patients with biliary cryptosporidiosis. The continued study of CD40 agonists in XHM is warranted.

Partial immune reconstitution of X-linked hyper IgM syndrome with recombinant CD40 ligand

X-linked hyper IgM syndrome (XHM) is a combined immune deficiency disorder caused by genetic alterations in CD40 ligand. The purpose of this study was to investigate the safety and efficacy of recombinant CD40 ligand (rCD40L) in the treatment of the disease. Three children were administered rCD40L subcutaneously 3 times per week at 0.03 mg/kg for 22 weeks, and after a 12-week drug-free interval, the dose was increased to 0.05 mg/kg for an additional 22 weeks of treatment. Although specific antibody responses to T cell-dependent antigens was lacking, administration of rCD40 resulted in acquisition of the capacity to mount cutaneous delayed type hypersensitivity reactions that disappeared during the drug-free interval as well as the postbiologic follow-up period. With rCD40L treatment, patient T cells developed a new capacity to respond to T-cell mitogens with synthesis of IFN-γ and TNF-α. Intracellular cytokine staining studies showed that both CD4(+) and CD8(+) T cells participated in this response. Finally, CD40L therapy was associated with changes in lymph node size and architecture based on comparison of biopsies taken before and after therapy. This clinical study showed that rCD40L is capable of improving T cell-immune function in patients with XHM.

Therapeutic interventions targeting CD40L (CD154) and CD40: the opportunities and challenges

CD40 was originally identified as a receptor on B-cells that delivers contact-dependent T helper signals to B-cells through interaction with CD40 ligand (CD40L, CD154). The pivotal role played by CD40-CD40L interaction is illustrated by the defects in B-lineage cell development and the altered structures of secondary lymphoid tissues in patients and engineered mice deficient in CD40 or CD40L. CD40 signaling also provides critical functions in stimulating antigen presentation, priming of helper and cytotoxic T-cells and a variety of inflammatory reactions. As such, dysregulations in the CD40-CD40L costimulation pathway are prominently featured in human diseases ranging from inflammatory conditions to systemic autoimmunity and tissue-specific autoimmune diseases. Moreover, studies in CD40-expressing cancers have provided convincing evidence that the CD40-CD40L pathway regulates survival of neoplastic cells as well as presentation of tumor-associated antigens to the immune system. Extensive research has been devoted to explore CD40 and CD40L as drug targets. A number of anti-CD40L and anti-CD40 antibodies with diverse biological effects are in clinical development for treatment of cancer and autoimmune diseases. This chapter reviews the role of CD40-CD40L costimulation in disease pathogenesis, the characteristics of therapeutic agents targeting this pathway and status of their clinical development.

Chronic intranasal administration of mould spores or extracts to unsensitized mice leads to lung allergic inflammation, hyper-reactivity and remodelling

Allergic asthma is a serious multifaceted disease characterized by eosinophil-rich airway inflammation, airway hyperreactivity and airway wall modifications known as remodelling. We previously demonstrated that the spores of two allergenic moulds, Alternaria alternata and Cladosporium herbarum, were potent inducers of immunoglobulin E (IgE) production. Moreover, mice sensitized by two intraperitoneal injections before intranasal challenge with A. alternata or C. herbarum spores developed an allergic lung inflammation and hyperreactivity. Here we report on the effect of chronic intranasal administration of C. herbarum spores or A. alternata extracts to unsensitized BALB/c mice. Our results demonstrate that this chronic treatment led to an increase of total serum IgE and the appearance of specific IgE and IgG1. Total cell number in bronchoalveolar lavage fluid from treated mice was highly increased compared to phosphate-buffered-saline-treated mice because of the accumulation of macrophages, neutrophils, lymphocytes and eosinophils. Airway hyperreactivity appeared after 3 weeks (extract) and 7 weeks (spores) and was maintained during the whole treatment. Increased interleukin-13 mRNA expression in the lungs and T helper type 2 cytokines (interleukin-4, -5, -6 and -13) and transforming growth factor-beta secretion in bronchoalveolar lavage fluid were also observed. Lung hydroxyproline and fibronectin contents indicated increased fibrosis in mice treated with mould allergen. These observations were confirmed by histological analysis demonstrating airway wall remodelling and strong mucus production. These observations show that this model, using chronic intranasal administration of relevant particulate allergens, is an interesting tool for the study of mechanisms leading to allergic pulmonary diseases and lung remodelling.

Autoreactive antibodies against neurons and basal lamina found in serum following experimental brain contusion in rats

BACKGROUND

Brain trauma is a risk factor for delayed CNS degeneration which may be attenuated by anti-inflammatory treatment. CNS injuries may cause anti-brain reactivity. This study was undertaken to analyze the pattern of delayed post-traumatic anti-brain immunity in experimental brain contusion.

METHOD

Adult Sprague-Dawley and Lewis rats were subjected to experimental brain contusions. For B-cell investigations, serum was obtained from contused, control and naïve rats, and used for immunohistochemistry on slices of rat brains to first detect autoreactive IgG and IgM antibodies in rat serum. Secondly, anti-rat IgG and IgM antibodies were used to search for auto-antibodies already bound to the brain tissue. Double staining with rat-serum and NeuN or anti-GFAP antibody was used to detect anti-neuronal and anti-astrocytic antibodies, respectively. For T-cell reactivity, cells from brains and cervical lymph nodes of rats were used in FACS analysis and elispot with MBP and MOG stimulation.

FINDINGS

Anti-vascular basal lamina IgG antibodies were detected at three months in 6/8 rats, following experimental contusion. Anti-neuronal IgG antibodies were detected 2 weeks after experimental contusion and sham surgery, while naïve controls were negative. Individual rats showed a prolonged response, or an anti-astrocytic staining. Tissue bound anti-self IgG or IgM was not detected in the brain tissue. Anti-MBP or anti-MOG T-cell responses were not detectable.

CONCLUSIONS

Experimental brain trauma and to some degree even sham surgery lead to an individually variable pattern of specific anti-brain reactive B-cells, while a T-cell response did not seem to be a consequence of moderate experimental contusion. The mere presence of anti brain-antibodies may be epiphenomenal, but could also be pathogenic for delayed degeneration. It is reasonable to regard the presence of an actual anti-brain reactivity as a potential threat to brain tissue integrity.

TACI and BAFF-R mediate isotype switching in B cells

The tumor necrosis factor family members BAFF and APRIL induce Ig isotype switching in human B cells. We analyzed the ability of BAFF and APRIL to induce isotype switching in murine B cells to IgG1, IgA, and IgE. APRIL and BAFF each engage two receptors, transmembrane activator and calcium-modulator and cytophilin ligand interactor (TACI) and B cell maturation antigen (BCMA), on B cells. In addition, BAFF engages a third receptor on B cells, BAFF-R. To determine the role of these receptors in isotype switching, we examined B cells from mice deficient in TACI, BCMA, and BAFF-R. The results obtained indicate that both TACI and BAFF-R are able to transduce signals that result in isotype switching.

CD40L, but not CD40, is required for allergen-induced bronchial hyperresponsiveness in mice

Asthma is characterized by immunoglobulin (Ig) E production, infiltration of the respiratory mucosa by eosinophils (EOSs) and mononuclear cells, and bronchial hyperresponsiveness (BHR). Interaction of CD40 on B cells and antigen presenting cells, with its ligand (CD40L) expressed transiently on activated T cells, is known to augment both T cell-driven inflammation and humoral immune responses, especially IgE production. Considering both the prominent role of inflammation in asthma and the association of the disease with IgE, we hypothesized that CD40-CD40L interactions would be important in pathogenesis. To test this hypothesis, we subjected wild-type (WT) mice and animals lacking either CD40 or CD40L to repeated inhalation of Aspergillus fumigatus (Af ) antigen. Af-treated WT mice displayed elevated IgE levels, bronchoalveolar lavage and pulmonary tissue eosinophilic inflammation, and BHR. IgE production was markedly suppressed in both the CD40 -/- and CD40L -/- strains. However, pulmonary inflammation did not appear to be inhibited by either of these mutations. Paradoxically, development of BHR was prevented by the lack of CD40L but not by the absence of CD40. We conclude that CD40/CD40L interactions, although critical in the induction of IgE responses to inhaled allergen, are not required for the induction of EOS-predominant inflammation. CD40L, but not CD40, is necessary for the development of allergen-induced BHR.

A phenotype map of the mouse X chromosome: models for human X-linked disease

The identification of many of the transcribed genes in man and mouse is being achieved by large scale sequencing of expressed sequence tags (ESTs). Attention is now being turned to elucidating gene function and many laboratories are looking to the mouse as a model system for this phase of the genome project. Mouse mutants have long been used as a means of investigating gene function and disease pathogenesis, and recently, several large mutagenesis programs have been initiated to fulfill the burgeoning demand of functional genomics research. Nevertheless, there is a substantial existing mouse mutant resource that can be used immediately. This review summarizes the available information about the loci encoding X-linked phenotypic mutants and variants, including 40 classical mutants and 40 that have arisen from gene targeting.

Neonatal immunology

The neonate, whether premature or of normal gestational age, is a unique host from an immunologic perspective. Many components of the immune system function less well in neonates compared with adults, giving rise to the concept of an "immunodeficiency of immaturity." The adaptive significance of these alterations for neonatal survival remains obscure. This review highlights some of the most prominent quantitative and qualitative differences between neonatal and adult immune systems. From a clinical standpoint, the most important differences appear to be (1) reduction in the available bone marrow reserve of granulocyte precursors, (2) reduction in serum complement activity, (3) decreased ability to produce antibodies against bacterial polysaccharide antigens, and (4) increased percentage of T lymphocytes bearing an antigenically "naive" cell surface phenotype and a correspondingly naive functional program.