Immunodeficiency With Hyper-IgM

About: Immunodeficiency With Hyper-IgM is a research topic. Over the lifetime, 34 publications have been published within this topic receiving 2673 citations.

Defective expression of T-cell CD40 ligand causes X-linked immunodeficiency with hyper-IgM

Abstract: X chromosome-linked immunodeficiency with hyper-IgM (HIGM1, MIM number 308230) is a rare disorder characterized by recurrent bacterial infections, very low or absent IgG, IgA and IgE, and normal to increased IgM and IgD serum levels. HIGM1 has been suggested to result from ineffective T-cell help for B cells. We and others have identified a novel, TNF-related activation protein (TRAP) that is exclusively expressed on the surface of stimulated T cells. TRAP, a type II transmembrane protein of M(r) 33,000, is the physiological ligand for CD40 (refs 5-8). Crosslinking of CD40 on B cells induces, in the presence of lymphokines, immunoglobulin class switching from IgM to IgG, IgA or IgE. Mapping of the TRAP gene to the X-chromosomal location q26.3-q27.1 (ref. 6) suggested a causal relationship to HIGM1, which had previously been assigned to Xq26 (refs 12-14). Here we present evidence that point mutations in the TRAP gene give rise to nonfunctional or defective expression of TRAP on the surface of T cells in patients with HIGM1. The resultant failure of TRAP to interact with CD40 on functionally intact B cells is responsible for the observed immunoglobulin isotype defect in HIGM1.

CD40 ligand mutations in X-linked immunodeficiency with hyper-IgM

Abstract: Signalling for the B-cell immunoglobulin isotype switch requires T-cell-derived cytokines and T-B cell interaction, which operates primarily through the CD40 molecule on B cells with its ligand (CD40L) on activated T cells (reviewed in ref. 1). The CD40L is a type II membrane protein with homology to tumour necrosis factor-alpha and -beta, and has important functions in B-cell activation and differentiation. Human CD40L maps on Xq26.3-27.1 (ref. 3), the region where a primary immunodeficiency characterized by an immunoglobulin isotype switch defect (the hyper-IgM immunodeficiency syndrome, HIGM1) has been localized. The hypothesis that HIGM1 involves an abnormality of the CD40L has been tested. We report here the lack of CD40L expression in four unrelated male children with the hyper-IgM syndrome. CD40L transcripts in these patients showed either deletions or point mutations clustered within a limited region of the CD40L extracellular domain. These genetic alterations with abnormal CD40L expression provide a molecular basis for immunoglobulin isotype switch defects observed in this immunodeficiency.

Immunodeficiency with hyper-IgM (HIM).

Abstract: Immunodeficiency with hyper-IgM (HIM) is a rare disorder characterized by recurrent infections associated with low IgG and IgA, and normal to increased IgM serum levels. Both primary and secondary forms of HIM syndrome have been reported. Among primary HIM syndrome, evidence for genetic heterogeneity is provided by the occurrence of the disease as X-linked, autosomal recessive, or autosomal dominant trait. The most common clinical manifestations include upper and lower respiratory tract infections, otitis, diarrhoea, oral ulcers, lymphoid hyperplasia, and autoimmunity. Recurrent neutropaenia is a frequent finding. Immunological abnormalities consist of lack of IgG and IgA secretion, and failure to respond to vaccination. Lymph nodes show absence of germinal centres. Few patients with a concurrent T-cell defect, and clinical expression of combined immune deficiency, have been reported. The gene responsible for the X-linked HIM syndrome (HIGM1) has been tentatively assigned to Xq24-27. However, carrier detection and prenatal diagnosis are not yet possible. Pathogenetic hypotheses include failure of B-cell differentiation, and defective regulation of immunoglobulin isotype switching due to abnormal T-cell-mediated signals. Treatment is mainly based upon regular administration of intravenous immunoglobulins. Steroids may be useful in the treatment of neutropaenia and of severe autoimmune manifestations.

Cholangiopathy and tumors of the pancreas, liver, and biliary tree in boys with X-linked immunodeficiency with hyper-IgM.

Abstract: We report an association between X-linked immunodeficiency with hyper-IgM (XHIM) and carcinomas affecting the liver, pancreas, biliary tree, and associated neuroectodermal endocrine cells. The tumors were fatal in eight of nine cases and in most instances were preceded by chronic cholangiopathy and/or cirrhosis. An additional group of subjects with XHIM had chronic inflammation of the liver or bile ducts but no malignancy. Many patients with XHIM were infected with cryptosporidia. CD40 is normally expressed on regenerating or inflammed bile duct epithelium. A CD40+ hepatocellular carcinoma cell line, HepG2, susceptible to cryptosporidia and CMV infection became resistant when cell surface CD40 was cross-linked by a CD40 ligand fusion protein. Apoptosis was triggered in HepG2 cells if protein synthesis was blocked by cycloheximide or if the cells were infected by cryptosporidia. Ligation of CD40 on biliary epithelium may contribute to defense against infection by intracellular pathogens. We propose that the CD40 ligand mutations that cause XHIM deprive the biliary epithelium of one line of defense against intracellular pathogens and that malignant transformation in the biliary tree follows chronic infection or inflammation. The resulting tumors may then progress without check by an effective immune response. Patients with XHIM who have abnormal liver function tests should be considered at increased risk for cholangiopathy or malignancy.

Defective Expression of CD40 Ligand on T Cells Causes “X‐Linked Immunodeficiency with Hyper‐IgM (HIGM1)”

Abstract: X-linked immunodeficiency with hyper-IgM (HIGM1) is a rare disorder, characterized by recurrent infections associated with very low or absent IgG and IgA, and normal to increased IgM serum levels. The disease has been earlier mapped to the q26-27 region of the X-chromosome. We have identified a novel molecule expressed on the surface of activated T cells, which was designated TRAP (Tumor necrosis factor Related Activation Protein), and could demonstrate that TRAP is a ligand for the CD40 receptor expressed on B cells. Our mapping of the TRAP gene to the Xq26.3-27.1 region suggested a causal relationship to HIGM1. Further work revealed that various mutations of the TRAP/CD40 ligand (CD40L) gene may lead to a defective expression of the TRAP/CD40L molecule on the T-cell surface in HIGM1 patients. A combination of structural and functional analyses finally demonstrated that the failure of TRAP/CD40L on T cells to interact with CD40 on B cells is responsible for the inefficient T-cell help for B cells observed in HIGM1. The observations made in HIGM1 allowed us to conclude that TRAP/CD40L is not required for IgM synthesis. In contrast, functional expression of TRAP is a prerequisite for effective immunoglobulin isotype switching and subsequent production of IgG, IgA and IgE by B cells in vivo. The interaction of TRAP/CD40L with CD40 thus provides a very critical link between the cellular and the humoral part of the immune system. The knowledge of TRAP/CD40L cDNA sequence, the availability of various reagents for the testing of expression and function of TRAP/CD40L, and our recent elucidation of the exon-intron structure of the TRAP/CD40L gene now provide all necessary tools for early diagnosis of affected patients and the detection of female carriers of HIGM1. The available information will also provide a basis for future attempts at gene therapy in this disease.