Double light chain producing lymphocytes: an enigma of allelic exclusion.

The infrequent double light chain producing lymphocyte (DLCPL) is discussed in the context of allelic exclusion. Principally allelic selection rather than allelic exclusion would suggest a role for the DLCPL in the normal B cell population rather than as an aberrance of B cell malignancy. Found primarily in the periphery, it is uncertain at what stage of B cell ontogeny the DLCPL might reside. Nevertheless, through the possible presentation of two functional surface receptors, the DLCPL could be capable of recognizing both self and nonself epitopes.

Double producers of kappa and lambda define a subset of B cells in mouse plasmacytomas.

Rearrangement of the light chain locus is believed to be an ordered process in which Iglambda rearrangements only occur if Igkappa rearrangements are found to be non-productive or self-reactive. Secondary rearrangements of the B-cell receptor (BCR) have shown, however, that rescue of abortive Igkappa rearrangements or autoreactive B cells can be achieved through receptor editing using upstream V-regions as the template sequences. Since secondary rearrangement can occur in the periphery, possibly in a subset of B cells maintaining constitutive Rag activity, it is conceivable that two light chains (kappa:kappa or kappa:lambda) could be expressed in these cells, apparently in violation of allelic exclusion. Previously, we have reported that silicone-induced plasmacytomas (SIPCs) exhibit dual expression and ongoing rearrangements of Igkappa and Iglambda. In this paper, we show by ELISA that both Igkappa and Iglambda are found at the protein level, but are secreted in different amounts. Furthermore, we demonstrate by micro-manipulation and RT-PCR amplification that Igkappa and Iglambda are simultaneously expressed in a single SIPC cell. We propose that these dual-expressing cells, found intermittently in cases of plasmacytomas (PCs), may have originally been immature B cells when transformed but now are maintained as a long-lived mature B cell found infrequently in the tumor population.

Restricted immunoglobulin variable region (Ig V) gene expression accompanies secondary rearrangements of light chain Ig V genes in mouse plasmacytomas.

The many binding studies of monoclonal immunoglobulin (Ig) produced by plasmacytomas have found no universally common binding properties, but instead, groups of plasmacytomas with specific antigen-binding activities to haptens such as phosphorylcholine, dextrans, fructofuranans, or dinitrophenyl. Subsequently, it was found that plasmacytomas with similar binding chain specificities not only expressed the same idiotype, but rearranged the same light (V(L)) and heavy (V(H)) variable region genes to express a characteristic monoclonal antibody. In this study, we have examined by enzyme-linked immunosorbent assay five antibodies secreted by silicone-induced mouse plasmacytomas using a broader panel of antigens including actin, myosin, tubulin, single-stranded DNA, and double-stranded DNA. We have determined the Ig heavy and light chain V gene usage in these same plasmacytomas at the DNA and RNA level. Our studies reveal: (a) antibodies secreted by plasmacytomas bind to different antigens in a manner similar to that observed for natural autoantibodies; (b) the expressed Ig heavy genes are restricted in V gene usage to the V(H)-J558 family; and (c) secondary rearrangements occur at the light chain level with at least three plasmacytomas expressing both kappa and lambda light chain genes. These results suggest that plasmacytomas use a restricted population of B cells that may still be undergoing rearrangement, thereby bypassing the allelic exclusion normally associated with expression of antibody genes.

[Micromethod for the identification of streptococcal, enterococcal and staphylococcal species]. / Microméthodes d'identification des Streptocoques, Enterocoques et des Staphylocoques.

The aim of this study was to set accurate and reliable methods in the identification of streptococcal, enterococcal and staphylococcal species. Micro CSB Strep and Staph system consists each of a strip with cupules containing dehydrated substrates for biochemical identification of bacterial species. Baye's theorem was used to validate tests. Reactions from micromethods were clear and easily read. Identification of 229 strains of streptococci and enterococci was correct for most species with 98.7% species with 99.3% sensitivity. 41 strains of staphylococci were also correctly identified with 85.2% of specificity and 97.68% of sensitivity.

Structural and affinity studies of IgM polyreactive natural autoantibodies.

Natural polyreactive autoantibodies (NAA) are an important component of the normal B cell repertoire. One intriguing characteristic of these Abs is their binding to various dissimilar Ags. It has been generally assumed that these Abs bind the Ags with low affinity, and are encoded by germline genes. We have used surface plasmon resonance to determine binding of avidities, and conducted a structural analysis of five murine monoclonal natural autoantibodies displaying a typical polyreactive binding pattern against cytoskeleton Ags and DNA. We show that 1) all the five Abs bind the different Ags with kinetic constants similar to those observed for immune Abs; 2) they express a restricted set of V(H) and V(L) genes, since the same V(H) gene is expressed by three out of the five, and one particular Vkappa gene was expressed twice. In addition, a single D gene segment was used by three of the five Abs; and 3) they express, in most cases, genes in a close germline configuration. Our amino acid sequence and modeling studies show that the distribution of exposed side chains in the NAA paratopes is close to the general pattern observed in the complementarity-determining regions (CDRs) of variable domains from immune Abs. Although CDR3 regions of the heavy chain have been postulated to play a major role in determining polyreactivity on the basis of recombinatorial experiments, our results failed to show any distinctive particularity of this region in terms of length or charge when compared with classical immune Abs.

Inhibition of human TNF alpha and LT in cell-free extracts and in cell culture by antisense oligonucleotides.

Antisense oligonucleotides (ODN), complementary to mRNA of human tumor necrosis factor alpha (TNF alpha) and lymphotoxin (LT) were tested for their ability to inhibit TNFs. TNFs production was studied in cell-free systems including wheat germ extract (WGE) and rabbit reticulocyte lysate (RRL). All ODN were effective in WGE at low concentration (0.2 microM), except those targeted to the 3' region of TNF alpha mRNA. A short ODN complementary to a common region between TNF alpha and LT inhibited both TNFs. In contrast, high ODN concentration (50 microM) was needed to inhibit LT mRNA translation in RRL, whereas no clear inhibition of TNF alpha was observed unless RNase H was added to the translation mixture. ODN effects on TNFs production by stimulated cell line in culture were also investigated. Three ODN-one located in the 5'-untranslated region, one spanning the AUG initiation codon and one downstream of this AUG-were the most effective sequences to decrease TNF alpha production. Two ODN targeted to the AUG initiation codon of LT were also able to inhibit its production. In conclusion we confirm the role of RNase H in cell free systems, and we found that there is no correlation between ODN efficiency in a cell-free system nor in cell culture. Efficient ODN could be used for in vitro investigation of the role of TNF alpha and LT in mechanism in which they are involved.

Differential regulation of TNF alpha, IL-1 beta, IL-6, IL-8, TNF beta, and IL-10 by pentoxifylline.

Pentoxifylline (PTX) is a methylxanthine drug known to inhibit the production of tumor necrosis factor-alpha (TNF alpha), which plays a key role in inflammation. Recent studies also revealed that other cytokines may be inhibited by PTX. We investigated PTX effects on production and mRNA expression of TNF alpha, IL-1 beta, IL-6, IL-8, TNF beta and IL-10. Cytokine release was studied in 1/10 diluted whole blood culture (WB) and in peripheral blood mononuclear cell (PBMC) culture. Cytokine production was triggered in both culture systems by endotoxin (LPS) or by phorbol ester (PMA) plus phytohemagglutinin (PHA). Our results showed that expression and production of TNF alpha and TNF beta were inhibited by PTX in a dose-dependent manner. Moreover, we observed that depending on the way of activating cells, PTX induced an up- or a down-regulation (in PMA + PHA or LPS stimulated cells, respectively) for IL-1 and IL-6 release. We also noted that the effects of PTX on IL-6, IL-8 and IL-10 production were different in WB and in PBMC culture. In conclusion PTX acts on cytokine in a complex manner depending on cellular environment and on the method of activation.

Expression and production of cytokines by heterohybrids and their parental B cells in CLL.

Three hybrids derived from CD5+ B cell chronic lymphocytic leukemia (B-CLL) and their parental B cells were studied for phenotypic evolution, immunoglobulin (Ig), tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) secretion. When phenotypic evolution was examined, hybrids showed the loss of classical B cell markers, indicating that they follow the same pattern of phenotypic differentiation as normal B cells. Hybrids displayed spontaneous high Ig secretion, which did not appear to be modified through stimulation by phorbol 12-myristate 13-acetate (PMA), recombinant interferon-gamma (rIFN-gamma) and Staphylococcus aureus Cowan I (SAC). Parental cells secreted minimal amounts of Ig spontaneously or through IFN-gamma and SAC stimulation, whereas PMA succeeded in increasing this secretion. An opposite pattern was observed when TNF-alpha and IL-6 secretion an expression at the mRNA level were assessed in hybrids and parental cells. TNF-alpha and IL-6 were spontaneously secreted by parental cells and this secretion was increased after PMA and SAC stimulation, both cytokine secretion and expression at the mRNA level were negative in hybrid cells. The absence of expression of these cytokines could be explained either by chromosomal loss or by down regulation. These results indicate that when parental CLL cells are induced to differentiate in the heterohybrid model, they acquire high spontaneous secretion of Ig, lose the classical B cell phenotypic markers and down regulate the expression of the cytokines studied.

Immunomodulation by cytokine antisense oligonucleotides.

The cytokine network is involved in normal immune reaction and in the progression of several pathologies. Antisense (AS) oligonucleotides, which allow specific inhibition of expression of proteins, offer a new methodology to investigate this complex network. This review focuses on the use of AS to modulate cytokine expression. AS may act in different ways such as blocking fixation or progression of the ribosome along the mRNA, mRNA cleavage by RNase H, or preventing normal RNA maturation. In order to improve AS efficiency, chemical modifications have been developed, and improvement of oligonucleotide uptake has been achieved with different systems of vectorization including liposomes (neutral, cationic, immunoliposome), nanoparticles, or covalent attachment of a carrier. In oncogenesis, intracellular or extracellular autocrine loops have been demonstrated by the use of cytokine AS. Involvement of cytokines in immunological reactions (TH1 and TH2 subset, IgE response, lymphokine activated killer, cytotoxic T lymphocyte...) and in hematopoiesis have also been studied with this approach. Therapeutic application of AS has been suggested by inhibition of inflammatory cytokines in vivo. Clinical trials using AS are under investigation in virological and in oncological diseases. At present, cytokine antisenses primarily represent a tool for dissecting the function of a cytokine in vitro, but they may offer in the future a new way for immunomodulation intervention.