http://repub.eur.nl/res/aut/5590/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/9926/ 2002-01-01T00:00:00Z Two polymorphisms of the human Ig(lambda) (IGL) locus have been described. The first polymorphism concerns a single, 2- or 3-fold amplification of 5.4 kb of DNA in the C(lambda)2-C(lambda)3 region. The second polymorphism is the Mcg(-)Ke(+)Oz(-) isotype, which has only been defined via serological analyses in Bence-Jones proteins of multiple myeloma patients and was assumed to be encoded by a polymorphic C(lambda)2 segment because of its high homology with the Mcg(-)Ke(-)Oz(-) C(lambda)2 isotype. It has been speculated that the Mcg(-)Ke(+)Oz(-) isotype might be encoded by a C(lambda) gene segment of the amplified C(lambda)2-C(lambda)3 region. We now unraveled both IGL gene polymorphisms. The amplification polymorphism appeared to result from a duplication, triplication, or quadruplication of a functional J-C(lambda)2 region and is likely to have originated from unequal crossing over of the J-C(lambda)2 and J-C(lambda)3 region via a 2.2-kb homologous repeat. The amplification polymorphism was found to result in the presence of one to five extra functional J-C(lambda)2 per genome regions, leading to decreased Ig(kappa):Ig(lambda) ratios on normal peripheral blood B cells. Via sequence analysis, we demonstrated that the Mcg(-)Ke(+)Oz(-) isotype is encoded by a polymorphic C(lambda)2 segment that differs from the normal C(lambda)2 gene segment at a single nucleotide position. This polymorphism was identified in only 1.5% (2 of 134) of individuals without J-C(lambda)2 amplification polymorphism and was not found in the J-C(lambda)2 amplification polymorphism of 44 individuals, indicating that the two IGL gene polymorphisms are not linked. http://repub.eur.nl/res/pub/9583/ 2001-01-01T00:00:00Z Regulation of allelic and isotypic exclusion of human immunoglobulin (Ig) light-chain genes was studied in 113 chronic B-cell leukemias as a "single-cell" model that allowed complete analysis of each light chain allele. Our data show that monospecific Ig light chain expression is in about 90% of cases determined by ordered recombination: Igkappa gene (IGK) rearrangements, followed by IGK deletions and Iglambda gene (IGL) rearrangements, resulting in the presence of only one functional Ig light chain rearrangement. In about 10% (10 cases), 2 functional Ig light chain rearrangements (IGK/IGL or IGL/IGL, but not IGK/IGK) were identified. This might be explained by the fact that regulation of the ordered recombination process is not fully strict, particularly when the IGL locus is involved. Unfavorable somatic mutations followed by receptor editing might have contributed to this finding. Eight of these 10 cases indeed contained somatic mutations. In cases with 2 functional Ig light chain rearrangements, both alleles were transcribed, but monospecific Ig expression was still maintained. This suggests that in these cases allelelic exclusion is not regulated at the messenger RNA level but either at the level of translation or protein stability or via preferential pairing of Ig light and Ig heavy chains. Nevertheless, ordered rearrangement processes are the main determinant for monospecific Ig light chain expression. http://repub.eur.nl/res/pub/18185/ 1997-06-26T00:00:00Z Lymphocytes form the specific immune system, capable of recognizing and responding to any foreign antigen, while remaining indifferent to self components. Throughout human life, lymphocytes are continuously generated from pluripotent hematopoietic stem cells. These hematopoietic stem cells are already detectable in the yolk sac and in the fetal liver from the second month of gestation onwards. After birth, the hematopoietic stem cells are mainly found in the bone marrow (BM). Two types of lymphocytes exist: B-lymphocytes and T-lymphocytes. Progenitor Bcells differentiate into mature B-lymphocytes in the BM, while progenitor T-cells differentiate into mature T-lymphocytes in the thymus. Mature B- and T-lymphocytes recognize foreign antigens via smface receptor molecules, the so-called antigen specific receptors. The antigen specific receptors of B-and T-lymphocytes are called B-cell receptor (BCR) or immunoglobulin (Ig) molecules and T-cell receptor (TCR) molecules, respectively. Differentiation of progenitor B-cells into mature B-lymphocytes is regulated via interaction with stromal cells in the BM. In the earliest stages, progenitor B-cells must be in direct contact with the stromal cells, and fmiher differentiation is dependent on growth factors, such as cytokines and hematopoietic growth factors, which are secreted by the stroma. These growth factors and cytokines induce proliferation, differentiation, and maturation in an organized way.