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.

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Keywords B-Lymphocytes/*cytology/drug effects, Bone Marrow Cells/*immunology, Case-Control Studies, Cell Differentiation/drug effects, Child, Preschool, DNA-Binding Proteins/*genetics/pharmacology/physiology, Family Health, Female, Flow Cytometry/methods, Gene Rearrangement/drug effects/genetics, Genes, Immunoglobulin, Genotype, Homeodomain Proteins/*genetics/pharmacology/physiology, Humans, Immunophenotyping, Infant, Male, Mutation, Nuclear Proteins, Research Support, Non-U.S. Gov't, Severe Combined Immunodeficiency/genetics/immunology/*pathology
Persistent URL hdl.handle.net/1765/8222
Journal Blood
Citation
Noordzij, J.G, de Bruin-Versteeg, S, Verkaik, N.S, Vossen, J.M.J.J, de Groot, R, Bernatowska, E, … van Dongen, J.J.M. (2002). The immunophenotypic and immunogenotypic B-cell differentiation arrest in bone marrow of RAG-deficient SCID patients corresponds to residual recombination activities of mutated RAG proteins. Blood. Retrieved from http://hdl.handle.net/1765/8222