http://repub.eur.nl/res/aut/4556/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/8235/ 2003-01-01T00:00:00Z Severe combined immunodeficiency disease (SCID) can be immunologically classified by the absence or presence of T, B, and natural killer (NK) cells. About 30% of T(-)B(-)NK(+) SCID patients carry mutations in the recombination activating genes (RAG). Some T(-)B(-)NK(+) SCID patients without RAG gene mutations are sensitive to ionizing radiation, and several of these radiosensitive (RS) SCID patients were recently shown to have large deletions or truncation mutations in the Artemis gene, implying a role for Artemis in DNA double-strand break (dsb) repair. We identified 5 RS-SCID patients without RAG gene mutations, 4 of them with Artemis gene mutations. One patient had a large genomic deletion, but the other 3 patients carried simple missense mutations in conserved amino acid residues in the SNM1 homology domain of the Artemis protein. Extrachromosomal V(D)J recombination assays showed normal and precise signal joint formation, but inefficient coding joint formation in fibroblasts of these patients, which could be complemented by the wild-type Artemis gene. The cells containing the missense mutations in the SNM1 homology domain had the same recombination phenotype as the cells with the large deletion, indicating that these amino acid residues are indispensable for Artemis function. Immunogenotyping and immunophenotyping of bone marrow samples of 2 RS-SCID patients showed the absence of complete V(H)-J(H) gene rearrangements and consequently a complete B-cell differentiation arrest at the pre-B-cell receptor checkpoint-that is, at the transition from CyIgmu(-) pre-B-I cells to CyIgmu(+) pre-B-II cells. The completeness of this arrest illustrates the importance of Artemis at this stage of lymphoid differentiation. http://repub.eur.nl/res/pub/31933/ 2002-06-19T00:00:00Z This thesis focuses on the immunological phenotype, the mutation analysis, and the residual activity of mutated proteins in patients with PID of the lymphoid system. During this project, we have investigated possible genotype-(immuno)phenotype relationships in patients with antibody deficiencies and SCID. Consequently, mutation analysis of the relevant genes formed an essential part of the study. Part 2 focuses on the laboratory diagnosis of patients with PID of the lymphoid system. In combination with clinical data. detailed immunophenotyping of PB and BM appeared to be essential to select possible candidate genes for mutation analysis (Chapter 2). Chapter 3 describes the pre-analytical. analytical, and post-analytical phases of mutation analysis and comments on the pitfalls that might occur when trying to establish a molecular diagnosis. Part 3 focuses on antibody deficiencies, with primary forms of agammaglobulinemia as the main topic (Chapters 6, 7 and 8). As agammaglobulinemia can result from an arrest in precursor B-ee!! differentiation in the BM. we have used detailed immunophenotyping of BM samples for assessment of the precise differentiation arrest. for identifying possible target genes, and for studying possible genotype-immunophenotype relationships. Part 4 focuses on SCID, especially patients suffering from T-B-NK+ SCID or OS caused by mutations in the RAG genes (Chapters II and 12). Whenever available, the BM samples of these B- SCID patients were subjected to detailed immunophenotyping. Furthermore, we tried to unravel the residual recombination activity of mutated RAG proteins via several approaches. In addition to in vitro analyses with RAG gene transfection and subsequent recombination of a plasmid recombination substrate as read-out system. we used Ig gene rearrangement patterns in BM samples as an in vivo read-out system of RAG protein function. Finally, Part 5 describes two patients with mycobacterial infections due to mutations in the gene encoding the interferon gamma receptor I chain (IFNGRJ). Although both patients suffered from complete signaling defects from the IFN-yR, one patient died at young age while the other patient is still alive without BM transplantation, showing the variability in clinical phenotypes in patients suffering from complete IFN-γR signaling defects. http://repub.eur.nl/res/pub/8222/ 2002-01-01T00:00:00Z The protein products of the recombination activating genes (RAG1 and RAG2) initiate the formation of immunoglobulin (Ig) and T-cell receptors, which are essential for B- and T-cell development, respectively. Mutations in the RAG genes result in severe combined immunodeficiency disease (SCID), generally characterized by the absence of mature B and T lymphocytes, but presence of natural killer (NK) cells. Biochemically, mutations in the RAG genes result either in nonfunctional proteins or in proteins with partial recombination activity. The mutated RAG genes of 9 patients from 7 families were analyzed for their recombination activity using extrachromosomal recombination substrates, rearrangement of endogenous Ig loci in RAG gene-transfected nonlymphoid cells, or the presence of Ig gene rearrangements in bone marrow (BM). Recombination activity was virtually absent in all 6 patients with mutations in the RAG core domains, but partial activity was present in the other 3 RAG-deficient patients, 2 of them having Omenn syndrome with oligoclonal T lymphocytes. Using 4-color flow cytometry, we could define the exact stage at which B-cell differentiation was arrested in the BM of 5 RAG-deficient SCID patients. In 4 of 5 patients, the absence of recombination activity was associated with a complete B-cell differentiation arrest at the transition from cytoplasmic (Cy) Igmu(-) pre-B-I cells to CyIgmu(+) pre-B-II cells. However, the fifth patient showed low frequencies of precursor B cells with CyIgmu and surface membrane IgM, in line with the partial recombination activity of the patient's mutated RAG gene and the detection of in-frame Ig gene rearrangements in BM. http://repub.eur.nl/res/pub/9829/ 2002-01-01T00:00:00Z X-linked agammaglobulinemia (XLA) is characterized by a severe B-cell deficiency, resulting from a differentiation arrest in the bone marrow (BM). Because XLA is clinically and immunologically heterogeneous, we investigated whether the B-cell differentiation arrest in BM of XLA patients is heterogeneous as well. First, we analyzed BM samples from 19 healthy children by flow cytometry. This resulted in a normal B-cell differentiation model with eight consecutive stages. Subsequently, we analyzed BM samples from nine XLA patients. Eight patients had amino acid substitutions in the Bruton's tyrosine kinase (BTK) domain or premature stop codons, resulting in the absence of functional BTK proteins. In seven of these eight patients a major differentiation arrest was observed at the transition between cytoplasmic Ig(mu-) pre-B-I cells and cytoplasmic Ig(mu+) pre-B-II cells, consistent with a role for BTK in pre-B-cell receptor signaling. However, one patient exhibited a very early arrest at the transition between pro-B cells and pre-B-I cells, which could not be explained by a different nature of the BTK mutation. We conclude that the absence of functional BTK proteins generally leads to an almost complete arrest of B-cell development at the pre-B-I to pre-B-II transition. The ninth XLA patient had a splice site mutation associated with the presence of low levels of wild-type BTK mRNA. His BM showed an almost normal composition of the precursor B-cell compartment, suggesting that low levels of BTK can rescue the pre-B-cell receptor signaling defect, but do not lead to sufficient numbers of mature B lymphocytes in the peripheral blood. http://repub.eur.nl/res/pub/9420/ 2000-01-01T00:00:00Z The proteins encoded by RAG1 and RAG2 can initiate gene recombination by site-specific cleavage of DNA in immunoglobulin and T-cell receptor (TCR) loci. We identified a new homozygous RAG1 gene mutation (631delT) that leads to a premature stop codon in the 5' part of the RAG1 gene. The patient carrying this 631delT RAG1 gene mutation died at the age of 5 weeks from an Omenn syndrome-like T(+)/B(- )severe combined immunodeficiency disease. The high number of blood T-lymphocytes (55 x 10(6)/mL) showed an almost polyclonal TCR gene rearrangement repertoire not of maternal origin. In contrast, B-lymphocytes and immunoglobulin gene rearrangements were hardly detectable. We showed that the 631delT RAG1 gene can give rise to an N-terminal truncated RAG1 protein, using an internal AUG codon as the translation start site. Consistent with the V(D)J recombination in T cells, this N-terminal truncated RAG1 protein was active in a plasmid V(D)J recombination assay. Apparently, the N-terminal truncated RAG1 protein can recombine TCR genes but not immunoglobulin genes. We conclude that the N-terminus of the RAG1 protein is specifically involved in immunoglobulin gene rearrangements.