Inducing the loss of immunoglobulin lambda light chain production and the rearrangement of a previously excluded allele in human plasma B cell lines with concanavalin A

Hydroxyl radical mediates the augmented angiotensin II responses in thoracic aorta of spontaneously hypertensive rats

AIM

To investigate the role of hydroxyl radical in augmented angiotensin II (Ang II) responses in the thoracic aorta of spontaneously hypertensive rats (SHR).

METHODS

To elucidate the role of hydroxyl radical, we used edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) as a tool for our study. The vascular responses to Ang II (10(-10) to 10(-6) mol/l), tert-butyl hydroperoxide (tBHP; 10(-6) to 10(-2) mol/l) and H(2)O(2) (10(-6) to 10(-2) mol/l) were constructed in aortic preparations obtained from control (WKY) and SHR in the absence and presence of edaravone.

RESULTS

The vascular responses to Ang II, tBHP and H(2)O(2) were found to be enhanced in aortic preparations from SHR as compared to control WKY rats. Edaravone selectively attenuated the augmented responses to Ang II but not to tBHP and H(2)O(2) suggesting that the .OH radical is involved in the augmented responses to Ang II. The elevated blood pressure in SHR was restored to a near normal value after 2 weeks of edaravone (10 mg kg(-1) i.p., b.i.d.) treatment.

CONCLUSION

From the results we infer that hydroxyl radical stress augments Ang II responses in the thoracic aorta of SHR and, by attenuating these enhanced vascular responses, edaravone could serve as an adjuvant antioxidant therapy for the vascular complications of hypertension.

Reactive oxygen species, cell growth, cell cycle progression and vascular remodeling in hypertension

Reactive oxygen species (ROS) include superoxide, hygrogen peroxide and hydroxyl radical. Under physiological conditions, all vascular cell types produce ROS in a controlled and regulated fashion, mainly through nonphagocyte NADPH oxidase. An imbalance between pro-oxidants and antioxidants results in oxidative stress. ROS are important intracellular signaling molecules. There is growing evidence that increased oxidative stress and associated oxidative damage are mediators of vascular injury in hypertension, as well as in other cardiovascular diseases. Oxidative stress causes vascular injury by reducing nitric oxide bioavailability, altering endothelial function and vascular contraction/dilation, promoting vascular smooth muscle cell proliferation and hypertrophy, and increasing extracellular matrix deposition and inflammation. The present review focuses on the regulatory role of ROS on cell growth and cell cycle progression and discusses implications of these events in vascular remodeling in hypertension.

Transcript expression of two Iglambda rearrangements and RAG-1/RAG-2 in a mature human B cell producing IgMlambda islet cell autoantibody

A human B cell clone, EBV-MB91, producing IgMlambda islet cell autoantibody (ICA), obtained by Epstein-Barr virus (EBV) transformation of peripheral CD5- surface Ig+ B cells from a Type 1 diabetic child, and an EBV-MB91-derived hetrohybridoma, HY-MB91, were analyzed for rearranged Ig genes. Both EBV-MB91 and HY-MB91 contained and expressed a unique IgH chain rearrangement (unmutated VH5-51-D6-19-JH5) but contained and expressed two Iglambda chain rearrangements: (i) Vlambda1-4-Jlambda3-Clambda3, which encoded the Iglambda chains (pI, 8.0) of IgMlambda-ICA, showing few mutations but consistent with Ag-driven selection according to the multinomial probability model; and (ii) Vlambda4-1-Jlambda3-Clambda3, with more mutations but inconsistent with antigen-driven selection and involving stop codons that precluded Iglambda synthesis. HY-MB91 showed a progressive loss of IgMlambda-ICA secretion, which was coupled with transcripts of the aberrant Vlambda4-1-Jlambda3-Clambda3 predominating (1.7-fold) over those of Vlambda1-4-Jlambda3-Clambda3. EBV-MB91 also showed the loss of IgMlambda-ICA secretion, associated with cell death. RAG-1 and RAG-2 transcripts occurred in EBV-MB91 but not in HY-MB91, indicating that the former but not the latter might have been able to exhibit V(D)J recombinase activity. Data show that a mature nonmalignant human B cell clone producing IgMlambda-ICA can express RAG-1/RAG-2 transcripts. That the aberrant Vlambda4-1-Jlambda3-Clambda3 was a nonproductive rearrangement occurring at the pre-B cell stage cannot be excluded. However, the hypothetical possibility that one of the two rearrangements corresponded to a secondary rearrangement occurring in the mature B cell represented by the EBV-MB91 clone might also be considered and is discussed.

Induction of light chain replacement in human plasma cells by caffeine is independent from both the upregulation of RAG protein expression and germ line transcription

When some human plasma cell lines are cultured with concanavalin A, the original light chain is replaced with another light chain which results from secondary VJ recombination (light chain shifting). We examined various intracellular factors involved in the induction of light chain shifting. Light chain shifting can be induced upon treatment with agents with phosphatase inhibitory activity such as caffeine and okadaic acid. Although the plasma cells used express both RAG-1 and RAG-2, the expression level of these proteins was not affected by caffeine or okadaic acid. Transcription of the germ line locus, which correlates to the locus activation for rearrangement, is also not influenced by phosphatase inhibition. However, the amount of signal broken-ended DNA intermediates generated during V(D)J rearrangement was shown to increase upon caffeine or okadaic acid treatment. The inhibitory activity of caffeine on phosphatase was the same as okadaic acid. However, caffeine exhibited much higher activity for VJ coding joint formation than okadaic acid. Therefore, although phosphatase inhibition might act, in part, on a mechanism by which V(D)J recombinase activity is regulated within the human plasma cells, other factor(s) are probably also involved in the process.

Acute production of vascular superoxide by angiotensin II but not by catecholamines

OBJECTIVE

To determine whether vascular superoxide is rapidly released by angiotensin II and is involved in vascular contraction.

DESIGN

The effect of superoxide dismutase (SOD) on angiotensin II induced elevation of mean arterial blood pressure was measured. Subsequently, acute production of vascular superoxide by angiotensin II and its effect on isometric tension were measured in rat aortic rings. The effects of catecholamines were concomitantly measured.

METHODS AND RESULTS

The acute pressor effects of angiotensin II were significantly reduced when rats were pretreated intravenously with SOD. When angiotensin II was added on aortic segments in the presence of Cypridina luciferin analog, immediate elevations of chemiluminescence were observed which were inhibited by SOD. Furthermore, angiotensin II-induced elevations of isometric tension in aortic rings were significantly reduced by SOD. The effects of epinephrine and norepinephrine were concomitantly measured and were not significant

CONCLUSIONS

The acute superoxide producing effect is likely to be specific to angiotensin II, because such a significant modification of the effects was not observed for catecholamines. Our results suggest that angiotensin II causes acute vascular superoxide production, which may be involved in the acute pressor effects.

Concanavalin A stimulation enhanced secondary VlambdaJlambda rearrangement in some human plasma B cells without up-regulation of recombination-activating gene expression and Vlambda germline transcription

Light chain shifting is a phenomenon that occurs in certain human antibody-producing plasma B cells which, when stimulated with concanavalin A (Con A), shift production of the original light chain to new light chains. Here we investigated the effect of Con A stimulation on these light chain shift-inducible cells. Analysis of transcripts and VJ-coding joints for new light chains revealed that a leaky amount of secondary VlambdaJlambda rearrangement occurs spontaneously, without Con A stimulation, and that Con A stimulation markedly increases VJ-coding joints and transcripts for new light chains. It was also shown that new light chain producers, which have carried out secondary rearrangement, do not further rearrange their light chain genes, even when stimulated with Con A. Recombination-activating gene (RAG) products and Vlambda germline transcription were constitutively expressed in these cell lines and their expression levels were not affected by Con A stimulation. These results suggest that Con A stimulation enhanced secondary VlambdaJlambda rearrangement, but this was not a result of the up-regulation of RAG expression and Vlambda germline transcription, which are believed to be sufficient for the process of VlambdaJlambda rearrangement.

Serum starvation induced secondary V lambda J lambda rearrangement in a human plasma B cell line

HB4C5 is a human antibody producing plasma B cell line that expresses the recombination activating gene-1 (RAG-1) and RAG-2 constitutively, but undergoes few secondary immunoglobulin gene rearrangements when cultured in fetal bovine serum-containing medium. Here, we found that depletion of serum from the culture media induces secondary VlambdaJlambda rearrangement in this cell line. To investigate the induction mechanism of secondary VlambdaJlambda rearrangement, we assessed the expression levels of RAG-1 and RAG-2 products, Vlambda germline transcription level and the amount of Vlambda signal broken ends (SBE) in HB4C5 cells cultured in serum-supplemented or serum-free medium. Western-blot analysis showed that the expression level for the RAG-1 and RAG-2 proteins was not affected by the serum depletion. Vlambda germline transcript was found to be constitutively expressed in HB4C5 cell line and this transcription level was not affected by the lack of serum. On the other hand, the amount of Vlambda SBE was shown to be increased in HB4C5 cells cultured in serum-free medium, suggesting that this increased formation of Vlambda SBE at least partly contributed to the enhanced occurrence of secondary VlambdaJlambda rearrangement in HB4C5 cells cultured in the serum-free condition. These results indicate that expression of RAG proteins and Vlambda germline transcription is not enough to undergo secondary VlambdaJlambda rearrangement in this cell line.

Light Chain Shifting: Identification of a Human Plasma Cell Line Actively Undergoing Light Chain Replacement

We identified an antibody-secreting human B-cell line (HTD8), which actively replaces the production of the original λ light chain with a new λ chain (light chain shifting) at a high rate. Loss of the original rearranged λ light chain occurs by significantly reducing the amount of transcript expressed. Expression of the new λ chain, which replaces the original λ chain, occurs by rearranging new VJ segments on a previously excluded allele. V λ gene usage of these new rearrangements are biased toward Vλ4, Vλ6, and Vλ10 families, which are known to be the least frequently used. In striking contrast to the plasma cell phenotype, recombination activating genes, RAG-1 and RAG-2, were expressed in the HTD8 cells and were shown to be necessary, but insufficient for inducing expression of the new λ chain. These results suggest that human plasma cells have the potential to actively undergo light chain replacement.

Light Chain Shifting: Identification of a Human Plasma Cell Line Actively Undergoing Light Chain Replacement

We identified an antibody-secreting human B-cell line (HTD8), which actively replaces the production of the original λ light chain with a new λ chain (light chain shifting) at a high rate. Loss of the original rearranged λ light chain occurs by significantly reducing the amount of transcript expressed. Expression of the new λ chain, which replaces the original λ chain, occurs by rearranging new VJ segments on a previously excluded allele. V λ gene usage of these new rearrangements are biased toward Vλ4, Vλ6, and Vλ10 families, which are known to be the least frequently used. In striking contrast to the plasma cell phenotype, recombination activating genes, RAG-1 and RAG-2, were expressed in the HTD8 cells and were shown to be necessary, but insufficient for inducing expression of the new λ chain. These results suggest that human plasma cells have the potential to actively undergo light chain replacement.

Cell hybridization, hybridomas, and human hybridomas

Cell hybridization is one of the most basic cytotechnologies. The hemagglutinating virus of Japan was first used to cause cell fusion; however, polyethylene glycol is widely used now because of simplicity of procedure. This chapter first explains the principles of cell hybridization methods and then describes the practical protocols for preparing mouse hybridomas using polyethylene glycol. So far, lack of an excellent human fusion partner cell line that has high fusion efficiencies and does not produce immunoglobulin has hindered the spread of human-human hybridoma preparation methods. In the authors' laboratory NAT-30 and HO-323, human parent cell lines with high fusion efficiencies, have been established to prepare many hybridoma cell lines producing cancer-specific human monoclonal antibodies. Because NAT-30 and HO-323 cell lines are IgM producers, it is difficult to obtain IgG-producing hybridomas because the types of immunoglobulin produced by hybridomas are strongly affected by the characteristics of parent cells. Thus a nonimmunoglobulin-producing human parent cell line, A4H12, derived from human T lymphoma was established that can efficiently obtain IgG-producing human hybridomas. Another problem with preparing human hybridomas is that it is difficult to obtain B lymphocytes immunized with optional antigens for ethical reasons. To overcome this problem, in vitro immunization methods have been developed that allow exposure of a large number of B lymphocytes to cultured cancer cell or soluble antigens. The section on human hybridomas explains human fusion partners, in vitro immunization methods, and the preparation of human-human hybridomas using an electrofusion method. Finally, the application of human monoclonal antibodies to medical uses and the preparation of supranatural monoclonal antibodies are reviewed. These include multifunctional monoclonal antibodies and altered monoclonal antibodies having increased affinity and specificity by exchanging or modifying light chains.

Further investigation of the light chain shifting phenomenon: light chain replacement through secondary rearrangement induced by lectin stimulation in the hybridoma cell line HB4C5

We found that when the hybridoma cell line HB4C5 was stimulated with wheat germ agglutinin (WGA), loss of production of the original lambda light chain occurred, followed by production of new light chain, which mirrored the reaction when stimulated with concanavalin A (ConA). We previously reported that the RAG genes are expressed not only in HB4C5 and its ConA-treated variant subclones, but also in the in the parental Namalwa cells, which are known to be in the plasma state. However, the new lambda light chains were expressed only in the HB4C5 cells and not in the parental Namalwa cells. Here we found that the RAG genes are expressed in HB4C5 cells after continuous stimulation with WGA. To further investigate the mechanism of this loss of original lambda light chain production by stimulation with lectins in HB4C5 cells, which leads to a sIg-negative subpopulation, we analyzed the differences between HB4C5 and Namalwa cells. In this present study, we found that a 70 kDa phosphorylated protein in HB4C5 cells became undetectable after stimulation with lectins (WGA and ConA), and was not detected in Namalwa cells before or after lectin stimulation. It has been believed that the RAG genes and loss of original lambda light chain production are required to induce expression of a new lambda light chain in the HB4C5 cells. We suggested that the phosphorylated 70 kDa protein in HB4C5 cells play important roles in regulating the production of new lambda light chains which is induced by lectins.

Germinal center development

Using a set of surface markers including IgD and CD38, human tonsillar B cells were classified into discrete subpopulations. Molecular and functional analysis allowed us to identify: i) two sets of naive B cells (Bm1 and Bm2); ii) germinal center founder cells (Bm2'); iii) an obscure population of germinal center B cells, displaying a high load of somatic mutations in IgV genes, C mu to C delta switch and preferential Ig lambda light chain usage: these cells may represent the precursors of normal and malignant IgD-secreting plasma cells; iv) the centroblasts (Bm3) in which somatic mutation machinery is activated; v) the centrocytes (Bm4) in which isotype switch occurs; vi) the memory B cells. The characterization of these subpopulations showed that: i) programmed cell death is set before somatic mutations, possibly providing an efficient way for affinity maturation; ii) only high affinity centrocytes are allowed to switch isotype; iii) CD40-ligation inhibits plasmacytic differentiation of mature B lymphocytes; iv) memory B cells preferentially differentiate into plasma cells; v) IgD isotype switch occurs in normal B cells; vi) receptor editing may be induced by somatic mutations in germinal centers. We also characterized two types of antigen-presenting cells in germinal centers: follicular dendritic cells that select high affinity B cells, and a new subset of germinal center dendritic cells that activate germinal center T cells.