Regulation of immunoglobulin light chain gene rearrangements during early B cell development in the human

Human autoantibody silencing by immunoglobulin light chains

Several newly arising human antibodies are polyreactive, but in normal individuals the majority of these potentially autodestructive antibodies are removed from the repertoire by receptor editing or B cell deletion in the bone marrow. To determine what proportion of naturally arising autoantibodies can be silenced by immunoglobulin (Ig) light chain receptor editing, we replaced the light chains in 12 such antibodies with a panel of representative Igκ and Igλ chains. We found that most naturally arising autoantibodies are readily silenced by light chain exchange. Thus, receptor editing may account for most autoreactive antibody silencing in humans. Light chain complementarity determining region (CDR) isoelectric points did not correlate with silencing activity, but Igλ genes were more effective than Igκ genes as silencers. The greater efficacy of Igλ chains as silencer of autoreactivity provides a possible explanation for the expansion and altered configuration of the Igλ locus in evolution.

Biases in Ig lambda light chain rearrangements in human intestinal plasma cells

Human intestinal lamina propria plasma cells are considered to be the progeny of chronically stimulated germinal centers located in organized gut-associated lymphoid tissues such as Peyer's patches and isolated lymphoid follicles. We have sampled human colonic lamina propria plasma cells and naive and memory B cell subsets from human Peyer's patches by microdissection of immunohistochemically stained tissue sections and used PCR methods and sequence analysis to compare IgVlambdaJlambda rearrangements in the plasma cell and B cell populations. Rearrangements that were either in-frame or out-of-frame between V and J were compared. Usage of IgVlambda families in the in-frame rearrangements from the plasma cells resembled that observed in the mantle cells, suggesting that antigenic selection for cellular specificity does not dramatically favor any particular Vlambda segment. However, in marked contrast, out-of-frame rearrangements involving Vlambda1 and Vlambda2 families are rarely observed in intestinal plasma cells, whereas rearrangements involving Vlambda5 are increased. This resulted in significantly biased ratios of in-frame:out-of-frame rearrangements in these Vlambda families. Out-of-frame rearrangements of IgVlambdaJlambda from plasma cells, including those involving the Vlambda5 family, have a significant tendency not to involve Jlambda1, consistent with the hypothesis that this population includes rearrangements generated by secondary recombination events. We propose that modification of out-of-frame rearrangements of IgVlambdaJlambda exists, probably a consequence of secondary rearrangements. This may be a mechanism to avoid translocations to susceptible out-of-frame IgVlambdaJlambda rearrangements during somatic hypermutation.

Analysis of a Clonally Related Mantle Cell and Hodgkin Lymphoma Indicates Epstein-Barr Virus Infection of a Hodgkin/Reed-Sternberg Cell Precursor in a Germinal Center

The simultaneous occurrence of a Hodgkin lymphoma (HL) and a non-Hodgkin lymphoma (NHL) is a rare event, and single cell analyses of such composite lymphomas revealed that NHL and Hodgkin/Reed-Sternberg (HRS) tumor cells are frequently descendants of the same tumor clone precursors. Here we present a composite lymphoma consisting of a mantle cell lymphoma (MCL) and an HL with EBV- and EBV+ HRS cells. Analysis of rearranged V genes of single cells revealed a clonal relationship between MCL and HL tumor cells. Although V gene rearrangements of the MCL were unmutated, mutations were observed in HRS cells. Besides mutations shared by all HRS cells, the EBV+ HRS cells carried identical additional mutations. These findings show that both lymphomas derive from a common precursor, most likely a pre germinal center (GC) B cell that already carried some transforming event(s). However, the presence of mutations in the V genes of the HRS cells further corroborates the importance of the GC reaction for the pathogenesis of HL. Importantly, the finding that only a subclone of the HRS clone, defined by a particular mutation pattern, was EBV infected represents a strong indication that EBV infection of the HRS cell precursor happened in the GC.

Expression of a targeted lambda 1 light chain gene is developmentally regulated and independent of Ig kappa rearrangements

Immunoglobulin light chain (IgL) rearrangements occur more frequently at Ig kappa than at Ig lambda. Previous results suggested that the unrearranged Ig kappa locus negatively regulates Ig lambda transcription and/or rearrangement. Here, we demonstrate that expression of a VJ lambda 1-joint inserted into its physiological position in the Ig lambda locus is independent of Ig kappa rearrangements. Expression of the inserted VJ lambda 1 gene segment is developmentally controlled like that of a VJ kappa-joint inserted into the Ig kappa locus and furthermore coincides developmentally with the occurrence of Ig kappa rearrangements in wild-type mice. We conclude that developmentally controlled transcription of a gene rearrangement in the Ig lambda locus occurs in the presence of an unrearranged Ig kappa locus and is therefore not negatively regulated by the latter. Our data also indicate light chain editing in approximately 30% of lambda 1 expressing B cell progenitors.

Antigen receptor selection by editing or downregulation of V(D)J recombination

Clonal selection is central to immune function, but it is complemented by "receptor selection", which regulates the immune repertoire not by cell death or proliferation but through the control of antigen receptor gene recombination. Inappropriate receptors, such as those that are autoreactive, underexpressed, or that fail to promote positive selection of thymocytes or B cells, stimulate secondary V-to-J recombinations that destroy and replace receptor genes. These processes play a central role in lymphocyte repertoire development. Recent work on the role of receptor selection in B and T cells has uncovered evidence for and against antigen-induced editing in thymocytes. Many studies suggest that editing plays a central role in B and T lymphocyte repertoire development. Important recent evidence has been uncovered addressing the role of tolerance-induced editing in thymocytes.

Models for antigen receptor gene rearrangement. III. Heavy and light chain allelic exclusion

The extent of allelic exclusion in Ig genes is very high, although not absolute. Thus far, it has not been clearly established whether rapid selection of the developing B cell as soon as it has achieved the first productively rearranged, functional heavy chain is the only mechanism responsible for allelic exclusion. Our computational models of Ag receptor gene rearrangement in B lymphocytes are hereby extended to calculate the expected fractions of heavy chain allelically included newly generated B cells as a function of the probability of heavy chain pairing with the surrogate light chain, and the probability that the cell would test this pairing immediately after the first rearrangement. The expected fractions for most values of these probabilities significantly exceed the levels of allelic inclusion in peripheral B cells, implying that in most cases productive rearrangement and subsequent cell surface expression of one allele of the heavy chain gene probably leads to prevention of rearrangement completion on the other allele, and that additional mechanisms, such as peripheral selection disfavoring cells with two productively rearranged heavy chain genes, may also play a role. Furthermore, we revisit light chain allelic exclusion by utilizing the first (to our knowledge) computational model which addresses and enumerates B cells maturing with two productively rearranged kappa light chain genes. We show that, assuming that there are no selection mechanisms responsible for abolishing cells expressing two light chains, the repertoire of newly generated B lymphocytes exiting the bone marrow must contain a significant fraction of such kappa double-productive B cells.

Immunoglobulin light chain gene rearrangements display hierarchy in absence of selection for functionality in precursor-B-ALL

The general order of the immunoglobulin (Ig) gene rearrangement process in human precursor-B cells is largely known. However, the exact Ig rearrangement patterns reflecting this process, especially those of the Ig light chain genes, are not well established. This requires detailed analysis of the gene configuration of all six IGH, IGK and IGL alleles at the single cell level. As such extensive analyses are difficult to perform in a reliable way within a single normal precursor-B cell, we used 169 precursor-B-ALL (ie six pro-B-ALL, 112 common ALL, and 51 pre-B-ALL) as clonal 'single cell' model system. The Ig gene recombinations show hierarchy starting with IGH gene rearrangements in all cases, followed by IGK rearrangements, IGK deletions and/or IGL rearrangements in 71% of cases. IGK deletions were found in the absence of IGL rearrangements in 34% of cases, which might be explained by the continuous recombinase activity in precursor-B-ALL, resulting in 'end-stage' IGK rearrangements, together with an apparently limited accessibility of the IGL locus. Remarkably, in 5% of cases IGL rearrangements took place in the absence of IGK rearrangements. In addition we found that in-frame IGH rearrangements are not necessarily required for the induction of Ig light chain gene rearrangements and that IGL rearrangements can be induced irrespective of the frame of the accompanying IGK rearrangements. In conclusion, precursor-B-ALL constitute a model system for studying Ig gene rearrangement processes without selection for functionality of the rearrangements or the influence of somatic hypermutations. Nevertheless, the hierarchy of IGH, IGK and IGL rearrrangements is apparent in precursor-B-ALL.