Magnetically localized and wash-free fluorescence immunoassay (MLFIA): proof of concept and clinical applications

Immunoassays are used for many applications in various markets, from clinical diagnostics to the food industry, generally relying on gold-standard ELISAs that are sensitive, robust, and cheap but also time-consuming and labour intensive. As an alternative, we propose here the magnetically localized and wash-free fluorescence immunoassay (MLFIA): a no-wash assay to directly measure a biomolecule concentration, without mixing nor washing steps. To do so, a fluorescence no-wash measurement is performed to generate a detectable signal. It consists of a differential measurement between the fluorescence of fluorophores bound to magnetic nanoparticles specifically captured by micro-magnets against the residual background fluorescence of unbound fluorophores. Targeted biomolecules (antibodies or antigens) are locally concentrated on micro-magnet lines, with the number of captured biomolecules quantitatively measured without any washing step. The performance of the MLFIA platform is assessed and its use is demonstrated with several biological models as well as clinical blood samples for HIV, HCV and HBV detection, with benchmarking to standard analyzers of healthcare laboratories. Thus, we demonstrated for the first time the versatility of the innovative MLFIA platform. We highlighted promising performances with the successful quantitative detection of various targets (antigens and antibodies), in different biological samples (serum and plasma), for different clinical tests (HCV, HBV, HIV).

Search for Effective Serum Tumor Markers for Early Diagnosis of Hepatocellular Carcinoma Associated with Hepatitis C

The aim of the study was to identify the most effective serum tumor markers for early diagnosis of hepatocellular carcinoma based on the combination of diagnostic characteristics and correlations.

NASH limits anti-tumour surveillance in immunotherapy-treated HCC

Hepatocellular carcinoma (HCC) can have viral or non-viral causes^1-5. Non-alcoholic steatohepatitis (NASH) is an important driver of HCC. Immunotherapy has been approved for treating HCC, but biomarker-based stratification of patients for optimal response to therapy is an unmet need^6,7. Here we report the progressive accumulation of exhausted, unconventionally activated CD8⁺PD1⁺ T cells in NASH-affected livers. In preclinical models of NASH-induced HCC, therapeutic immunotherapy targeted at programmed death-1 (PD1) expanded activated CD8⁺PD1⁺ T cells within tumours but did not lead to tumour regression, which indicates that tumour immune surveillance was impaired. When given prophylactically, anti-PD1 treatment led to an increase in the incidence of NASH-HCC and in the number and size of tumour nodules, which correlated with increased hepatic CD8⁺PD1⁺CXCR6⁺, TOX⁺, and TNF⁺ T cells. The increase in HCC triggered by anti-PD1 treatment was prevented by depletion of CD8⁺ T cells or TNF neutralization, suggesting that CD8⁺ T cells help to induce NASH-HCC, rather than invigorating or executing immune surveillance. We found similar phenotypic and functional profiles in hepatic CD8⁺PD1⁺ T cells from humans with NAFLD or NASH. A meta-analysis of three randomized phase III clinical trials that tested inhibitors of PDL1 (programmed death-ligand 1) or PD1 in more than 1,600 patients with advanced HCC revealed that immune therapy did not improve survival in patients with non-viral HCC. In two additional cohorts, patients with NASH-driven HCC who received anti-PD1 or anti-PDL1 treatment showed reduced overall survival compared to patients with other aetiologies. Collectively, these data show that non-viral HCC, and particularly NASH-HCC, might be less responsive to immunotherapy, probably owing to NASH-related aberrant T cell activation causing tissue damage that leads to impaired immune surveillance. Our data provide a rationale for stratification of patients with HCC according to underlying aetiology in studies of immunotherapy as a primary or adjuvant treatment.

Clinical and Experimental Evaluation of Diagnostic Significance of Alpha-Fetoprotein and Osteopontin at the Early Stage of Hepatocellular Cancer

We evaluated the possibility of using an experimental model of hepatocellular carcinoma to study oncomarkers of primary liver cancer and compared the diagnostic efficacy of alpha-fetoprotein and osteopontin in the experiment and in clinical practice. Experimental studies were performed on a model of hepatocellular carcinoma induced by administration of diethyl nitrosamine to Fisher-344 rats. In addition, the levels of α-fetoprotein and osteopontin were determined in 35 patients with hepatocellular carcinoma detected at stages I-II according to TNM classification. The proposed model of liver cancer in rats reflects the sequence of stages characteristic of hepatocellular carcinoma in humans: liver fibrosis-cirrhosis-cancer. This model is applicable for the study of tumor markers at the early stage of tumor development. Osteopontin was found to have a more powerful diagnostic potential then alpha-fetoprotein.

[Application of alpha-fetoprotein and osteopontin combination for early diagnosis of hepatocellular carcinoma associated with hepatitis C.]

Liver cirrhosis in the outcome of hepatitis C is the leading cause of hepatocellular carcinoma (HCC) in the world. Early diagnosis and timely treatment of HCC are important for reducing mortality and increasing life expectancy of patients with hepatocellular carcinoma. To assess the risk of HCC, the definition of alpha-fetoprotein (AFP) in the blood is most widely used, but low sensitivity limits its diagnostic value. In 2012, a new HCC biomarker - osteopontin (OPN), which is a secreted phosphoprotein that has a high affinity for integrins was proposed. The level of acute renal failure begins to rise in the early stages of malignancy, before the period of HCC detection by imaging methods, and has significantly better sensitivity than AFP. The purpose of this study is to evaluate the diagnostic efficacy of the combined determination of alpha-fetoprotein and osteopontin in prospective monitoring of patients with chronic hepatitis C in the advanced phase of liver fibrosis. Monitoring of 588 patients with hepatitis C was carried out from February 2013 to February 2019. HCC was detected in 55 of them (2.6% per year). The combination of 2 biomarkers showed better diagnostic efficacy than alpha-fetoprotein and osteopontin separately: AUC 0.85 (95% CI 0.80-0.90) versus AUC 0.63 (95% CI 0.57-0, 70) and AUC 0.82 (95% CI 0.77-0.88), respectively. This combination showed a sensitivity of 85.5% and made it possible to diagnose HCC with a prognostic level of a positive result of 72.3% at 19,4±0,8 weeks before the diagnosis was confirmed by instrumental imaging methods (ultrasound, MRI, CT). In the combined variant, ARF made the greatest contribution to the increase in diagnostic efficacy (AUC). At an early and very early stage of HCC development, isolated HCC elevations were found in only 5.4% of patients. Conclusion: the combined use of alphafetoprotein and osteopontin as a diagnostic panel can be recommended for monitoring patients with liver cirrhosis in the outcome of hepatitis C and predicting HCC at an early stage of development.

Developmental regulation of p53-dependent radiation-induced thymocyte apoptosis in mice

The production of T cell receptor αβ(+) (TCRαβ(+) ) T lymphocytes in the thymus is a tightly regulated process that can be monitored by the regulated expression of several surface molecules, including CD4, CD8, cKit, CD25 and the TCR itself, after TCR genes have been assembled from discrete V, D (for TCR-β) and J gene segments by a site-directed genetic recombination. Thymocyte differentiation is the result of a delicate balance between cell death and survival: developing thymocytes die unless they receive a positive signal to proceed to the next stage. This equilibrium is altered in response to various physiological or physical stresses such as ionizing radiation, which induces a massive p53-dependent apoptosis of CD4(+) CD8(+) double-positive (DP) thymocytes. Interestingly, these cells are actively rearranging their TCR-α chain genes. To unravel an eventual link between V(D)J recombination activity and thymocyte radio-sensitivity, we analysed the dynamics of thymocyte apoptosis and regeneration following exposure of wild-type and p53-deficient mice to different doses of γ-radiation. p53-dependent radio-sensitivity was already found to be high in immature CD4(-) CD8(-) (double-negative, DN) cKit(+) CD25(+) thymocytes, where TCR-β gene rearrangement is initiated. However, TCR-αβ(-) CD8(+) immature single-positive thymocytes, an actively cycling intermediate population between the DN and DP stages, are the most radio-sensitive cells in the thymus, even though their apoptosis is only partially p53-dependent. Within the DP population, TCR-αβ(+) thymocytes that completed TCR-α gene recombination are more radio-resistant than their TCR-αβ(-) progenitors. Finally, we found no correlation between p53 activation and thymocyte sensitivity to radiation-induced apoptosis.

Multiple sclerosis-associated retrovirus particles cause T lymphocyte-dependent death with brain hemorrhage in humanized SCID mice model

A retroviral element (multiple sclerosis-associated retrovirus, MSRV) defining a family of genetically inherited endogenous retroviruses (human endogenous retrovirus type W, HERV-W) has been characterized in cell cultures from patients with multiple sclerosis. Recently, MSRV retroviral particles or the envelope recombinant protein were shown to display superantigen activity in vitro, but no animal model has yet been set up for studying the pathogenicity of this retrovirus. In the present study, the pathogenicity of different sources of MSRV retroviral particles has been evaluated in a hybrid animal model: severe combined immunodeficiency (SCID) mice grafted with human lymphocytes and injected intraperitoneally with MSRV virion or mock controls. MSRV-injected mice presented with acute neurological symptoms and died within 5 to 10 days post injection. Necropsy revealed disseminated and major brain hemorrhages, whereas control animals did not show abnormalities (P <.001). In ill animals, reverse transcriptase-polymerase chain reaction (RT-PCR) analyses showed circulating MSRV RNA in serum, whereas overexpression of proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma was evidenced in spleen RNA. Neuropathological examination confirmed that hemorrhages occurred prior to death in multifocal areas of brain parenchyma and meninges. Further series addressed the question of immune-mediated pathogenicity, by inoculating virion to SCID mice grafted with total and T lymphocyte-depleted cells in parallel: dramatic and statistically significant reduction in the number of affected mice was observed in T-depleted series (P <.001). This in vivo study suggests that MSRV retroviral particles from MS cultures have potent immunopathogenic properties mediated by T cells compatible with the previously reported superantigen activity in vitro, which appear to be mediated by an overexpression of proinflammatory cytokines.

Simultaneous evaluation of lymphocyte subpopulations in the liver and in peripheral blood mononuclear cells of HCV-infected patients: relationship with histological lesions

ABBREVIATIONS

Intrahepatic lymphocytes are believed to be involved in the immunopathogenesis of hepatitis C virus (HCV) infection and the evolution of HCV-induced hepatitis. In the present study, we examined the three main intrahepatic lymphocyte subsets, namely CD3+CD56- conventional T lymphocytes, CD3+CD56+ natural T (NT) lymphocytes and CD3-CD56+ natural killer (NK) lymphocytes in HCV-infected patients. The proportion of each lymphocyte subset was evaluated both in liver biopsies and in samples of peripheral blood lymphocytes (PBL) by flow cytometry in 21 patients with histologically proven chronic hepatitis C. Simultaneously, alanine aminotransferase (ALT) levels, viral load and histological lesions were assessed. Neither NT nor NK populations correlated with any biochemical, viral or histological parameters. Furthermore, Valpha24+ NT lymphocytes showed no preferential enrichment in the liver of HCV-infected patients. Regarding conventional T lymphocytes, a highly significant linear correlation was found between intrahepatic CD3+CD56- T lymphocytes and the Knodell score, a numerical score for assessing histological activity and fibrosis (r = 0.715, P < 0.0001) and more specifically with the periportal necrosis parameter, which is the main lesion of chronic hepatitis C. In addition, analysis of the peripheral compartment revealed a high correlation between values of CD3+CD56- lymphocytes and both Knodell score (r = 0.624, P = 0.003) and serum ALT levels and again with periportal necrosis. The strong correlation between the proportion of peripheral CD3+CD56- conventional T lymphocytes and the severity of hepatic lesions leads us to propose that evaluation of this accessible peripheral population could be used as an indicator test for the severity of histological lesions in chronic hepatitis C.

Immunotherapy by non-myeloablative stem cell transplantation: study of the immune reconstitution. Arguments for distinct cell subsets in skin and blood

INTRODUCTION

Non-myeloablative peripheral stem cell transplantation has been shown to induce tumour rejection in patients with acute leukaemia. However, the immunological mechanisms involved and the immune reconstitution achieved have not been investigated.

MATERIALS AND METHODS

We describe the cases of two patients for whom we have studied the lymphocyte reconstitution achieved, using both phenotypic and genetic analyses of the T-cell repertoire, after peripheral stem cell transplantation.

RESULTS

: In both cases we observed immune reconstitution with T-cell repertoire evolution and presence of activated CD8(+) T cells. In one of the patients an activated clone expressing Vbeta8 represents 46% of the CD8(+) cells. Expansion of this clone occurred in the absence of graft vs host disease symptoms. In the second case a skin lesion typical of graft vs host disease appeared after complete remission had been achieved. The T-cell repertoire in a biopsy of the lesion was distinct from that observed in the blood.

CONCLUSION

Our study indicates that peripheral donor cells can effectively reconstitute a grafted patient while inducing an immune response against antigens expressed by the leukaemic/myeloma cells. Our data provide arguments for different populations of T cells associated with graft vs leukaemia/lymphoma and GVH effects.

TCRA gene rearrangement in immature thymocytes in absence of CD3, pre-TCR, and TCR signaling

During thymocyte differentiation, TCRA genes are massively rearranged only after productively rearranged TCRB genes are expressed in association with pTalpha and CD3 complex molecules within a pre-TCR. Signaling from the pre-TCR via the CD3 complex is thought to be required to promote TCRA gene accessibility and recombination. However, alphabeta(+) thymocytes do develop in pTalpha-deficient mice, showing that TCRalpha-chain genes are rearranged, either in CD4(-)CD8(-) or CD4(+)CD8(+) thymocytes, in the absence of pre-TCR expression. In this study, we analyzed the TCRA gene recombination status of early immature thymocytes in mutant mice with arrested thymocyte development, deficient for either CD3 or pTalpha and gammac expression. ADV genes belonging to different families were found rearranged to multiple AJ segments in both cases. Thus, TCRA gene rearrangement is independent of CD3 and gammac signaling. However, CD3 expression was found to play a role in transcription of rearranged TCRalpha-chain genes in CD4(-)CD8(-) thymocytes. Taken together, these results provide new insights into the molecular control of early T cell differentiation.

Multiple sclerosis retrovirus particles and recombinant envelope trigger an abnormal immune response in vitro, by inducing polyclonal Vbeta16 T-lymphocyte activation

A retroviral element (MSRV) defining a family of genetically inherited endogenous retroviruses (HERV-W) has recently been characterized in cell cultures from patients with multiple sclerosis (MS). To address the possible relationship with MS, direct detection of circulating virion RNA was proposed but revealed technically difficult to perform in standardized conditions, in the face of multiple endogenous HERV-W copies. A parallel approach has evaluated MSRV potential pathogenicity in relation to characteristic features of multiple sclerosis, in particular, T-lymphocyte-mediated immunopathology. We report here that MSRV particles induce T-lymphocyte response with a bias in the Vbeta16 chain usage in surface receptor, whatever the HLA DR of the donor. A recombinant MSRV envelope-but not core-protein reproduced similar nonconventional activation. Molecular analysis of Vbeta CDR3 showed that Vbeta16 expansions are polyclonal. Our results thus provide evidence that MSRV envelope protein can trigger an abnormal immune response with similar characteristics to that of superantigens.

Both TCR alpha and TCR delta chain diversity are regulated during thymic ontogeny

TCRalpha and TCRdelta chains are coded by a common genetic locus using a single set of V gene segments (ADV segments). This article addresses the question of regulation of the use of the ADV segments by the TCRalpha and TCRdelta chains. Using both qualitative and quantitative analyses we have studied the use of 23 ADV gene families as part of TCRalpha and TCRdelta transcripts. A number of previously undetected rearrangement and transcription events are described, indicating that the intrathymic TCRdelta repertoire is much more diverse than previously supposed. Repertoire analysis at several developmental time points allowed the description of regulated waves of ADV gene use, not only for TCRdelta chains, but also for TCRalpha chains, during thymic ontogeny. Control of these waves appears to be linked directly to the ADV segments and their local chromatin environment, which may change over the course of T cell differentiation.

Murine dendritic cells derived from myeloid progenitors of the thymus are unable to produce bioactive IL-12p70

Dendritic cells (DC) are present at low density in the thymus where they mediate negative selection of self-reactive thymocytes. Previous reports suggest that thymic DC (TDC) are a single population of lymphoid-related DC. In this study, we documented the presence in the adult mouse thymus of an additional population of TDC exhibiting a myeloid phenotype (CD11c(+) CD8alpha(-) CD11b(+)). This population, which can be purified, represented approximately 20% of the total TDC and differs from the population of lymphoid TDC (CD11c(+) CD8(+) CD11b(-)) by its incapacity to produce IL-12p70 under double stimulation by LPS and anti-CD40. Furthermore, using an original culture system allowing expansion of DC from myeloid progenitors, we demonstrated that DC exhibiting a similar myeloid phenotype can be derived from a common DC/macrophage progenitor resident in the adult mouse thymus. We found that, in contrast with myeloid splenic DC expanded in the same conditions, these cultured TDC were unable to produce IL-12p70 under double stimulation by LPS and anti-CD40 or LPS and IFN-gamma. Thus, our results suggest that 1) adult mouse thymus contains at least two phenotypically and functionally distinct populations of DC; and 2) cultured myeloid DC derived from thymus and spleen differ by their ability to produce IL-12p70. The mechanisms underlying the differences in IL-12-secreting capacities of the cultured splenic and thymic DC are under current investigation.

Preferential ADV-AJ association during recombination in the mouse T-cell receptor alpha/delta locus

The gene coding for a T-cell receptor (TCR) alpha chain is assembled from variable (ADV) and joining (AJ) genes located on Chromosome 14. Each of the 90 ADV genes can rearrange with any one of the 61 AJ genes. We have previously demonstrated that ADV and AJ gene segment use evolves with time, with a progressive opening of ADV and AJ regions of the locus. To define the rules governing the use of AJ genes by ADV genes belonging to one family, we carried out a detailed analysis of 268 combinations of ADV2 BALB/c transcripts. We found that the different ADV2 members use different sets of AJ genes depending on their location within the ADV locus: ADV2S7 (the most AJ proximal ADV2 member) rearranges mainly with the AJ genes located close to the TEA element, whereas 50% of the sequences for ADV2S8, which is distal to the AJ locus, use the most distal AJ genes. ADV2S5, an ADV2 member located in the middle of the ADV locus, is associated with a wider set of AJ genes, located in the center of the AJ locus. Taken together, our results indicate that, in addition to the progressive opening of the ADV and AJ loci, the chromosomal location of ADV and AJ genes is a factor affecting AJ use in BALB/c mice.

Pairing of Vbeta6 with certain Valpha2 family members prevents T cell deletion by Mtv-7 superantigen

Superantigens (SAg) are proteins of bacterial or viral origin able to activate T cells by forming a trimolecular complex with both MHC class II molecules and the T cell receptor (TCR), leading to clonal deletion of reactive T cells in the thymus. SAg interact with the TCR through the beta chain variable region (Vbeta), but the TCR alpha chain has been shown to have an influence on the T cell reactivity. We have investigated here the role of the TCR alpha chain in the modulation of T cell reactivity to Mtv-7 SAg by comparing the peripheral usage of Valpha2 in Vbeta6(+) (SAg-reactive) and Vbeta8.2(+) (SAg non-reactive) T cells, in either BALB/D2 (Mtv-7(+)) or BALB/c (Mtv-7(-)) mice. The results show, first, that pairing of Vbeta6 with certain Valpha2 family members prevents T cell deletion by Mtv-7 SAg. Second, there is a strikingly different distribution of the Valpha2 family members in CD4 and CD8 populations of Vbeta6 but not of Vbeta8.2 T cells, irrespective of the presence of Mtv-7 SAg. Third, the alpha chain may play a role in the overall stability of the TCR/SAg/MHC complex. Taken together, these results suggest that the Valpha domain contributes to the selective process by its role in the TCR reactivity to SAg/MHC class II complexes, most likely by influencing the orientation of the Vbeta domain in the TCR alphabeta heterodimer.

Tetanus toxin L chain is processed by major histocompatibility complex class I and class II pathways and recognized by CD8+ or CD4+ T lymphocytes

Tetanus toxin (TeNT) is a heterodimeric protein antigen, whose light chain (L) is translocated in the cytosol of neuronal target cells specifically to cleave its substrates, vesicle-associated membrane protein-2 (VAMP-2, or synaptobrevin) or cellubrevin. We report that the L chain behaves as a nominal antigen recognized by specific T-cell clones upon either class I- or II-restricted presentation. Three types of responses are observed: (i) a TeNT- and L-specific CD8+ T-cell response, that can be inhibited in a dose-dependent manner by the proteasome inhibitor clasto-Lactacystin beta-lactone; (ii) a CD4+ T-cell response specific for L but not TeNT, with recognition of a determinant processed in a chloroquine-sensitive and brefeldin A-resistant compartment; (iii) a CD4+ T-cell response against both L and TeNT, with processing in a brefeldin A-sensitive compartment. The L chain processing was investigated in U937 cells by internalization and localization of L chain by separation of the cell content by differential centrifugation experiments. After incubation with TeNT or L chain in the presence of H chain, the L chain was predominantly distributed in the cytosolic fraction, whereas incubation with L alone led to localization in a lysosome/membrane fraction. The distribution of the TeNT L chain in both cytosolic and endocytic compartments of the antigen-presenting cell accounted for its processing by both class I and class II pathways. Furthermore, an epitope overlapping with the zinc-binding region was recognized by CD4+ and CD8+ T cells.

A two-step culture method starting with early growth factors permits enhanced production of functional dendritic cells from murine splenocytes

Dendritic cells (DC) are professional antigen presenting cells (APC) able to activate naive T cells and initiate the immune response. They are present in most tissues at very low concentrations and are difficult to isolate. DC can be obtained in larger numbers by their propagation from progenitors present in blood, bone marrow and spleen. However, biochemical studies and biological analysis of DC functions require very large numbers of these cells. In this paper, we described a two-step culture system using unfractionated splenocytes from BALB/c mice as a source of DC progenitors. The proliferative capacity of the progenitors is amplified in the first step of the culture (day 0-6) using different combinations of early acting cytokines combined or not with granulocyte-macrophage CSF (GM-CSF). The second step of the culture starts at day 6 with the removal of early growth factors in order to allow the differentiation and final maturation of DC during 2-3 weeks of culture with flt-3 ligand (flt-3L) and GM-CSF. The addition of Stem Cell Factor (SCF) or IL-6 to the standard combination of flt-3L+/-GM-CSF produces a large increase in the proliferation of GM and DC progenitors (28 times and 11 times respectively) in the first step of the culture. This proliferative wave of DC progenitors is followed by the production of a high percentage of immature and mature DC in flt-3L+GM-CSF stimulated cultures. The best combination of early cytokines in terms of proliferative activity and subsequent level of DC production was flt-3L+IL-6+GM-CSF, which permitted the generation of 1 to 2x10(9) DC from one single spleen. Using this growth factor cocktail, a mixture of immature (2/3) and mature (1/3) DC was produced until day 14 of culture, and levels of MHC class II and costimulatory molecules (CD40, B7.2) increased between 2 and 4 weeks of incubation, or within 2 days when stimulated by IL-4 or LPS. The splenic DC produced after 2 weeks of culture are fully functional, exhibiting a high capacity of endocytosis when immature, a strong stimulatory reactivity in mixed leukocyte reaction and consistently producing high levels of bioactive IL-12 p70 after CD 40 ligation in the presence of LPS between 13 and 43 days of culture.

TCR alpha-chain repertoire in pTalpha-deficient mice is diverse and developmentally regulated: implications for pre-TCR functions and TCRA gene rearrangement

Pre-TCR expression on developing thymocytes allows cells with productive TCRB gene rearrangements to further differentiate. In wild-type mice, most TCRA gene rearrangements are initiated after pre-TCR expression. However, in pTalpha-deficient mice, a substantial number of alphabeta+ thymocytes are still produced, in part because early TCR alpha-chain expression can rescue immature thymocytes from cell death. In this study, the nature of these TCR alpha-chains, produced and expressed in the absence of pre-TCR expression, have been analyzed. We show, by FACS analysis and sequencing of rearranged transcripts, that the TCRA repertoire is diverse in pTalpha-/- mice and that the developmental regulation of AJ segment use is maintained, yet slightly delayed around birth when compared with wild-type mice. We also found that T cell differentiation is more affected by pTalpha inactivation during late gestation than later in life. These data suggest that the pre-TCR is not functionally required for the initiation and regulation of TCRA gene rearrangement and that fetal thymocytes are more dependent than adult cells on pTalpha-derived signals for their differentiation.

Co-operation between human CR1 (CD35) and CR2 (CD21) in internalization of their C3b and iC3b ligands by murine-transfected fibroblasts

CR1 and CR2 are expressed as associated proteins on the B-lymphocyte surface. To investigate their respective contributions to the internalization of C3 fragments, transfected murine fibroblasts expressing human CR1, CR2, or both CR1 and CR2 were produced. CR1- and CR1-CR2-expressing cells bound C3b and C3b-dimer whereas CR2- and CR1-CR2-expressing cells bound iC3b and C3de. In all cases, maximum binding was achieved at low ionic strength. CR1-CR2-positive cells internalized two- to threefold more C3b and 1.5-fold more iC3b than CR1- and CR2-single-positive cells, respectively. Internalization of the anti-CR1 antibody J3D3, or C3de was at the same level, in both double-transfected and single-transfected cells. Furthermore, the internalization of C3b dimer by CR1-CR2 cells was impaired in the presence of OKB7, an anti-CR2-blocking antibody, but it was not altered in CR1 cells. Taken together, these findings suggest that CR1 and CR2 collaborate to internalize C3b and iC3b proteins. We suggest that the induction of conformational changes of the ligands enhances their binding to both receptors.

Importance of thioredoxin in the proteolysis of an immunoglobulin G as antigen by lysosomal Cys-proteases

For disulphide-bonded antigens, reduction has been postulated to be a prerequisite for proteolytic antigen processing, with subsequent production of major histocompatibility complex (MHC) class II binding fragments. The murine monoclonal immunoglobulin G (IgG) CE25/B7 was used as a multimeric antigen in a human model. Native IgG is highly resistant to proteolysis and has been previously found to be partially reduced at early steps of cell processing to become a suitable substrate for endopeptidases. The role of the oxidoreductase thioredoxin (Trx) was assessed in the reduction of the IgG by cleavage of H-L and H-H disulphide bonds. Recombinant human Trx (rTrx) has been assayed in a proteolytic in vitro system on IgG using endosomal and lysosomal subcellular fractions from B lymphoblastoid cells. rTrx is required in a dose-dependent manner for development of efficient proteolysis, catalysed by thiol-dependent Cys-proteases, such as cathepsin B. We demonstrated that cathepsin B activity was stimulated by the addition of rTrx. Thus, we propose that Trx-dependent IgG proteolysis occurred, on the one hand by means of the unfolding of the IgG after disulphide reduction, becoming a substrate of lysosomal proteases, and on the other hand by Cys-proteases such as cathepsin B that are fully active upon the regeneration of their activity by hydrogen donors.

Different stimulating effects of complement C3b and complete Freund's adjuvant on antibody response

Upon activation, complement C3 undergoes a conformational change and acquires the capacity to covalently bind to other proteins such as antigen and to interact with specific receptors; therefore, C3 is involved in cell mediated immune response. The adjuvant effect produced by linking C3-fragments to antigen has recently been described. We injected C3b-Ag complexes consisting of one molecule of C3b ester linked to one molecule of HEL to immunised mice, and we compared the C3b adjuvant activity with that of complete Freund's adjuvant. IgG titers elicited by HEL emulsified in CFA (HEL + CFA) were higher than those elicited by HEL-C3b, but decreased rapidly after a peak response around day 45 whereas HEL-C3b resulted in a continuous increase of anti-HEL response. Mice immunised with HEL + CFA then boosted with HEL-C3b gave significantly higher response than those boosted with HEL + CFA, indicating more efficient memory cell restimulation by C3b. HEL + CFA leads to better priming than HEL-C3b when mice are boosted with HEL-C3b. Thus, adjuvant effect of C3b is different from that of CFA, leading to more stable IgG production and better memory stimulation.

Amplification of the antibody response by C3b complexed to antigen through an ester link

Complement C3 has been described as playing an important role in the cell-mediated immune response. C3b has the capacity to covalently bind Ag and then to stimulate in vitro Ag presentation to T lymphocytes. To verify this observation in vivo, we prepared and purified covalent human C3b-Ag complexes using lysozyme (HEL) as Ag. The characterization of these HEL-C3b complexes indicates that they are representative of those susceptible to be generated in physiological conditions. Mice were immunized with 0.1 to 0.6 microgram of either free HEL, HEL + C3b, HEL-C3b, or HEL + CFA. Response was assessed after two i.p. injections by quantification of specific Ab production. Immunization with either HEL-C3b complexes or HEL + CFA leads to anti-HEL IgG production whereas free HEL or HEL + C3b was ineffective. Either HEL-C3b or HEL + CFA immunizations led to a similar Ig subclass patterns, including IgG1, IgG2a, IgA, and IgM. Our experiments provide the first evidence for modulation of specific Ab response by C3b when it is bound to Ag through a physiological-like link. Taken together with previous data concerning Ab response following recombinant HEL-C3d immunization, cellular events such as processing of C3b-Ag by APC and recognition by T lymphocytes, this present result underlines the importance of C3b and its fragments in stimulation of the immune system, through the multiplicity and complementarity of its interactions.

[Role of the complement C3 protein in the control of the specific immune response]

Whereas complement system was usually considered as a member of innate defence, one of its components (C3) is now thought to facilitate acquired immunity. This role is due first to its capacity to covalently bind to antigens and secondly to the interactions of its proteolytic fragments with different receptors expressed on most cells involved in the acquired immune response. After activation in the plasma, C3 is proteolysed in fragments which possess various biological activities, as a modification in cell activities occurred after binding to cell surface receptors. Injection of low amount of antigen results in a modified immune response in C3 deficient animals with a decrease in the level of specific antibodies and an absence of IgM/IgG switch. One of the fragments of C3 (C3d) and its receptor (CR2) seem particularly important : knock out animals in C3 or CR2 have similar phenotypes. Mice with a deficit in CR2 restricted to the B lymphocytes present a strong reduction in the number and the size of germinal centers. Moreover, expression of CR2 on follicular dendritic cells is necessary for the generation of a strong memory response. C3 is also involved in the control of the intracellular processing of the antigen as the use of covalent complex (C3b-antigen) instead of free antigen increases the amount of stable MHC class II molecules at the antigen presenting cells surface. In summary, C3 fragments increase cell to cell interactions, induce intracellular signalling after binding to their receptors and increases intracellular processing of antigens. A better knowledge of the different roles of C3 may be useful to modify the immune response and to promote the immune memory, a domain where C3 seems particularly important.

Purification of intracellular compartments involved in antigen processing: a new method based on magnetic sorting

In the present study, we describe a method to specifically isolate intracellular compartments containing endocytosed antigen. We have demonstrated that isolated compartments represent a small proportion of the intracellular material, highly enriched in antigen. Antigen-containing vesicles are specifically sorted from other intracellular compartments, such as endoplasmic reticulum or Golgi apparatus, and from the plasma membrane. They remain functional in vitro since they can be acidified, and the antigen inside has been found to be partially proteolysed. In macrophages, kinetic analysis has revealed that the antigen is first found in compartments of endosomal density, carrying Rab 5 and Rab 7, then in late compartments of lysosomal density, which are rich in proteases. The global protein content of the compartments was mapped by two-dimensional electrophoresis. In B lymphocytes, this method has allowed the isolation of endocytic compartments emerging from receptor-mediated endocytosis of the antigen. After 2 h of chase, the antigen reached vesicles containing large amounts of MHC-class II molecules, invariant chain and human leucocyte antigen-DM, where peptide loading can occur.

Use of TCR ADV gene segments by the delta chain is independent of their position and of CD3 expression

The CD3 signaling complex is required for cell surface expression and selection of both alphabeta and gammadelta TCR. In this study we analyzed TCRD transcripts in both wild-type and CD3-epsilon-deficient mice. We show that the repertoire of ADV segments used by the delta chain is unchanged in the latter. Not all ADV genes participate in making up the TCRD repertoire. However, their use does not depend on their distance from the other TCRD-forming segments. For example ADV12, situated at more than 870 kb from the DD region, is expressed as part of TCRD transcripts, whereas ADV8, members of which are proximal to the DD region, is not. These data suggest that the accessibility of ADV8 gene segments is differentially regulated during T cell development in the thymus. Taken together, our results suggest that TCRA and TCRD rearrangements are independently controlled, and that the absence of TCRA expression in CD3-epsilon-deficient mice is not due to a lack of accessibility of the ADV gene segments but rather to inaccessibility of the AJ gene region.

Differential chronology of TCRADV2 gene use by alpha and delta chains of the mouse TCR

The genes coding for TCR alpha and delta chains share the same genetic locus (TCRA/D). The rules governing the utilization of a V gene with the alpha and delta chains have not been established. More specifically, it is not known whether the position of a gene within the locus influences its utilization in alpha and delta TCR. To elucidate these points, we mapped ADV2 genes in the TCRA/D locus of BALB/c mice and analyzed their utilization in TCR alpha and delta transcripts from thymi isolated from mice of different ages. Our results show that all ADV2 genes can be used by the two chains, but with strikingly different patterns. Moreover, ADV2 utilization by the alpha chain proceeds in successive concentric waves during development, suggesting a progressive regulation of gene accessibility and utilization. These results support independent control of TCRA and TCRD gene assembly.

Complement C3b fragment covalently linked to tetanus toxin increases lysosomal sodium dodecyl sulfate-stable HLA-DR dimer production

Processing and presentation of covalently linked C3b-tetanus toxin (TT) complexes, as compared to unlinked C3b + TT, lead to increased T cell proliferation. The aim of this study was to analyze the effect of coupling C3b to TT on the efficiency of TT peptide loading on HLA-DR1 molecules. In the Epstein-Barr virus-transformed B cell line HOM 2, we detected a significant increase of sodium dodecyl sulfate (SDS)-stable major histocompatibility complex (MHC) class II molecules after exposure to C3b-TT as compared to unlinked C3b and TT. The ratio of compact form/unbound form (C/U ratio) obtained with C3b-TT as antigen (Ag) is about twice that obtained with uncomplexed TT + C3b as Ag. Similar results were obtained using HLA-DR1-transfected fibroblasts that do not express C3b complement receptors, indicating that the SDS-stable HLA-DR1 increase did not result simply from C3b opsonization but rather from a direct effect of C3b-TT linkage on peptide generation. Exposure of HOM 2 cells to C3b-TT resulted in an increase in concentration of SDS-stable HLA-DR molecules in lysosomes but not in endosomes. Thus, C3b attachment to Ag induces a redistribution of peptide/MHC complex which results in a higher efficiency of Ag presentation by MHC class II molecules.

V alpha domain modulates the multiple topologies of mouse T cell receptor V beta20/staphylococcal enterotoxins A and E complexes

The superantigens staphylococcal enterotoxin A and E (SEA and SEE) both contact major histocompatibility complex (MHC) class II molecules on two sites located on the alpha and beta chains. We have investigated the role of the T cell receptor (TCR) alpha chain in the modulation of the various topologies of TCR/SEA (or SEE)/class II complexes. For this purpose, we have used three mouse V beta20 T cell lines expressing different V alpha domains and two T cell hybridomas expressing mouse V beta1 or V beta11 segments. The response of these T cells to SEA and SEE was studied in the context of presentation by wild-type human MHC class II molecules; or by mutants on MHC, in each of the two superantigen binding sites (position alpha39K and beta81H) to which the superantigens can still bind but with an altered conformation. Although V beta20 T cell lines are efficiently stimulated using SEA and SEE presented by wild-type HLA-DR1 molecules, our results show that the nature of the TCR V alpha domain can affect differently the recognition of the toxins bound to mutant class II molecules. This suggests that various functional topologies exist for both SEA and SEE/class II complexes and that the T cell response to each of these complexes can be modulated by the V alpha domain of the TCR. Interestingly, the recognition of SEA and SEE is achieved in different fashions by a given V beta20 T cell line.

Heat shock increases antigenic peptide generation but decreases antigen presentation

The heat shock response is a universal and highly conserved cellular response to stress. We describe here the effect of elevated temperature on the capacity of B cells to present antigen. Heat shock markedly affects the ability of these cells to process and present tetanus toxin to class II-restricted T cell clones. Inhibition of antigen presentation is due neither to a modification of antigen capture nor to a variation of major histocompatibility complex (MHC) class II molecule synthesis and cell surface expression. Stressed and nonstressed B cells are able to present peptides loaded at the cell surface with the same efficiency. Nevertheless, heat shock leads to an increase of antigen peptide generation in subcellular compartments; an enhancement of cathepsin B activity is also observed. These data suggest that such a stress induces a failure in the intracellular peptide loading onto MHC class II molecules.

Germline genomic structure of the B10.A mouse Tcra-V2 gene subfamily

The number of mouse Tcra-V gene segments varies from one individual to another and is estimated to be about 100. Southern blot analysis revealed that most of the Tcra-V are organized in clusters composed of copies of Tcra-V belonging to different subfamilies. We analyzed in detail a Tcra-V subfamily and looked for new Tcra-V in order to improve the knowledge of the mouse Tcra locus organization. A series of genomic clones derived from the B10.A mouse strain enclosing these clusters was used to determined the structure of all the Tcra-V2. We were able to identify ten Tcra-V2. This study showed that the Tcra-V2 can be organized into three structural subgroups. The distribution of the genes along the Tcra locus, plus their structural organization, indicates that successive duplications occurred during the processes of expansion and contraction of the Tcra-V gene subfamilies. Several Tcra-V2 are also identical, indicating recent duplications. The most divergent Tcra-V2 differ by 7.4% nucleotides, leading to 5.2% differences in amino acid contents.

Bacterial superantigen specificities of mouse T cell receptor V beta 20

The study of the mouse T cell receptor (TcR) beta chain repertoire in BALB/c thymocytes led to the identification of the V beta 20 gene segment. The expression of V beta 20 estimated at the transcriptional level differs among mouse strains, suggesting clonal deletion. In the present study, we reconstituted by transfection functional TcR using the V beta 20 segment with different V alpha segments and studied the action of superantigen toxins. The V beta 20-transfectant T cells are activated by staphylococcal enterotoxins A and E (SEA and SEE) but not by the other tested toxins. The activation is dependent on the presence of cells expressing major histocompatibility complex class II molecules. Different HLA DR alleles can present the bacterial toxins, establishing that they interact with TcRV beta 20 as superantigens. Moreover, the V alpha domain associated with the V beta 20 domain has an influence on the response to these toxins. The fact that V beta 20 is recognized by SEA and SEE, although both toxins are known to interact with different sets of V beta, suggests the presence of different TcR binding sites on the toxins.

Two-hybrid system screen with the small GTP-binding protein Rab6. Identification of a novel mouse GDP dissociation inhibitor isoform and two other potential partners of Rab6

Rab6 is a small GTP-binding protein that belongs to the Ras superfamily and is involved in intra-Golgi transport. Using a two-hybrid system screen of a mouse brain cDNA library, we have isolated several clones encoding proteins that interact with Rab6. Approximately 60% of the clones identified encoded a new mouse Rab GDP dissociation inhibitor (GDI) isoform. This GDI isoform is distinct from mouse mGDI-1 and mGDI-2, which have been characterized previously, and most likely represents the mouse counterpart of the rat Rab GDI beta isoform. In the two-hybrid system, GDI beta interacts with wild-type Rab6 and Rab5, but not with a GTP-bound Rab6 mutant, or a Rab6 mutant that cannot be post-translationally processed. We further examined whether mouse GDI beta is functional; we show that recombinant mouse GDI beta is able to remove several Rab proteins, including Rab1, Rab2, Rab4, and Rab6, from membranes. The identification of a third GDI isoform in mouse raised the question whether GDI genes belong to a larger multigenic family. We have shown, by Southern blot analysis of genomic DNA, that at least five GDI gene copies exist in both the mouse and rat genomes. In our two-hybrid screen, we have also characterized another clone that specifically interacts with Rab6. This clone was partially sequenced but shows no homology to known sequences. Finally, a third clone, interacting with both Rab5 and Rab6, also appears to encode a novel protein.

T cell receptor V beta repertoire in mice lacking endogenous mouse mammary tumor provirus

When endogenous mouse mammary tumor virus (MMTV) superantigens (SAg) are expressed in the first weeks of life an efficient thymic deletion of T cells expressing MMTV SAg-reactive T cell receptor (TcR) V beta segments is observed. As most inbred mouse strains and wild mice contain integrated MMTV DNA, knowing the precise extent of MMTV influence on T cell development is required in order to study T cell immunobiology in the mouse. In this report, backcross breeding between BALB.D2 (Mtv-6, -7, -8 and -9) and 38CH (Mtv-) mice was carried out to obtain animals either lacking endogenous MMTV or containing a single MMTV locus, i.e. Mtv-6, -7, -8 or -9. The TcR V beta chain (TcR V beta) usage in these mice was analyzed using monoclonal antibodies specific for TcR V beta 2, V beta 3, V beta 4, V beta 5, V beta 6, V beta 7, V beta 8, V beta 11, V beta 12 and V beta 14 segments. Both Mtv-8+ mice and Mtv-9+ mice deleted TcR V beta 5+ and V beta 11+ T cells. Moreover, we also observed the deletion of TcR V beta 12+ cells by Mtv-8 and Mtv-9 products. Mtv-6+ and Mtv-7+ animals deleted TcR V beta 3+ and V beta 5+ cells, and TcR V beta 6+, V beta 7+ and V beta 8.1+ cells, respectively. Unexpectedly, TcR V beta 8.2+ cells were also deleted in some backcross mice expressing Mtv-7. TcR V beta 8.2 reactivity to Mtv-7 was shown to be brought by the 38CH strain and to result from an amino acid substitution (Asn-->Asp) in position 19 on the TcR V beta 8.2 fragment. Reactivities of BALB.D2 TcR V beta 8.2 and 38CH TcR V beta 8.2 to the exogenous infectious viruses, MMTV(SW) and MMTV(SHN), were compared. Finally, the observation of increased frequencies of TcR V beta 2+, V beta 4+ and V beta 8+ CD4+ T cell subsets in Mtv-8+ and Mtv-9+ mice, and TcR V beta 4+ CD4+ T cells in Mtv-6+ and Mtv-7+ mice, when compared with the T cell repertoire of Mtv- mice, is consistent with the possibility that MMTV products contribute to positive selection of T cells.

T cell regulation of collagen-induced arthritis in mice. III. Is T cell vaccination a valuable therapy?

Since T cells play a critical role in collagen-induced arthritis (CIA), CD4+ T cell hybridomas were derived from DBA/1 mice immunized with bovine type II collagen (CII). The hybrid clones selected were Thy-1-2+, CD4+, CD8-, T cell receptor (TcR) alpha beta + and produced interleukin-2 in response to CII peptides presented by I-Aq molecules. The clones were collagen type-specific and recognized CII from many species except the mouse. More precisely, the reactivity was directed against the immunodominant cyanogen bromide-cleaved fragment CB11(II). Analysis of the TcR carried by the T cell hybridomas showed that they used identical V alpha and J alpha (V alpha BMB, J alpha 20) gene segments and two distinct V beta (V beta 1 and V beta 4) associated with the J beta 2.5 gene segment. Interestingly, the junctional regions were highly conserved in structure and length. These findings may indicate a strong in vivo selection by the antigen for a particular combination of both alpha and beta chains of the TcR. Inoculation of irradiated anti-CII T cell hybrids into DBA/1 mice, before priming with CII, altered the course of the disease resulting in either a long-lasting suppression or an exacerbation of CIA whereas a control CD4+ hybridoma with an unrelated specificity did not influence the development of arthritis. However, the regulatory effect of anti-CII T cell clones was unpredictable, suggesting that the TcR structure may not solely account for the modulation of CIA and that T cell vaccination is not a reliable method for inducing suppression of CIA.

Neonatal deletion and selective expansion of mouse T cells by exposure to rabies virus nucleocapsid superantigen

The nucleocapsid (NC) of the rabies virus behaves as an exogenous superantigen (SAg) in humans. In the present report, we analyzed whether it is also a SAg in mice by studying the effect of NC on T cell receptor (TCR) V beta expression in BALB/c mice. Repeated injection of NC in newborn BALB/c mice led to a marked reduction by two- to sixfold of V beta 6 expressing CD4+ T cells in spleen and in peripheral blood. Decrease of V beta 6-expressing CD3+ mature T cells was also observed in thymus. Single NC injection in footpad resulted in a three- to sixfold expansion of V beta 6 CD4+ T cells, but not of CD8+ T cells, in the draining lymph nodes of BALB/c mice. The intensity of the stimulation was dose dependent and was maximal 3 d after the NC injection. The clonal deletion of T cells bearing a particular V beta demonstrates that NC is a SAg in mice. T cells, especially CD4+ T cells, are an essential factor in host resistance to rabies virus and also in the pathophysiology of paralysis; thus, we postulate that a rabies virus component, which stimulates T cells, such as a SAg, may increase virus immunopathogenicity. To evaluate this hypothesis, we compared the course of rabies in adult BALB/c lacking V beta 6, 7, 8.1, and 9 T cells and in normal BALB/c. Immune-related paralysis was decreased in BALB/c missing the NC target V beta T cells. Transfer of V beta 6 but not of V beta 8.1-3 T cells into recipient mice lacking V beta 6, 7, 8.1, and 9 allowed the immune-related paralysis to evolve. Taken together, these results strongly support the hypothesis that T cells expressing rabies SAg-specific V beta 6 T cells, are involved in the genesis of the immunopathology that is characteristic of paralytic rabies.

Analysis of the nucleotide sequence variation of the antigen-binding domain of DR alpha and DQ alpha molecules as related to the evolution of papillomavirus-induced warts in rabbits

We previously found that regression of skin warts induced by the Shope cottontail rabbit papillomavirus in New Zealand White rabbits, as well as malignant conversion of persistent warts, are linked to a restriction fragment length polymorphism of the major histocompatibility complex class II DR alpha and DQ alpha genes. To find out whether this immunogenetic control could be connected with the antigen binding and presentation function of the alpha 1 domain of class II molecules, we have sequenced the exon 2 of the four DR alpha EcoRI and six of the seven DQ alpha PvuII restriction fragment length polymorphism alleles identified, and deduced the encoded amino acid sequences. We found no amino acid polymorphism among DR alpha alleles, indicating that the alpha 1 domain of the DR alpha chain does not condition wart regression or cancer development. In contrast, 27 of the 82 amino acids of the DQ alpha 1 domain were found variable, defining five amino acid sequence alleles. The restriction fragment length polymorphism allele linked to regression and another allele not linked to regression share the same alpha 1 domain, indicating that wart regression is rather conditioned by a closely linked gene. The most divergent DQ alpha 1 allele, however, was that associated with a higher risk of cancer. Alignment of rabbit and human DQ alpha exon 2 alleles disclosed that amino acid charge variations occur at positions assumed to be important for peptide binding in humans. By modulating the affinity for tumor-specific antigenic peptides, such transitions could affect immune surveillance and, thus, condition the risk for progression to carcinoma of papillomavirus-associated lesions.

T cell receptor V alpha gene segment with alternate splicing in the junctional region

The locus encoding mouse TCR-alpha chain includes approximately 100 V alpha gene segments that can be organized in about 20 structural subfamilies. Southern blot analysis of a T cell line derived from the BALB/c strain, M5T, has indicated that both alpha loci were rearranged, as assessed by the deletion of the delta locus, and that the V alpha gene segment involved in one of the rearrangements did not belong to any of the V alpha subfamilies already described. Transcripts of TCR-alpha chains from the M5T line were cloned after cDNA synthesis and anchored-polymerase chain reaction, revealing a V alpha gene segment of an as yet unidentified subfamily, V alpha 5T. Molecular cloning of germ-line V alpha 5T gene segments has shown that this subfamily contained two members, one of them being a pseudogene. The two members were located to each extremity of the alpha locus associated with a member of the V alpha 13 and V alpha BWB subfamilies. Analysis of transcripts bearing the V alpha 5T gene segment in the M5T line as well as in thymocytes has revealed that J alpha are frequently absent. This is due to an alternate donor splice site generated at the V alpha 5T-J alpha junction that leads to a splicing from the end of V alpha 5T to C alpha instead of the J alpha to C alpha conventional splicing. The impact of J alpha spliced-out transcripts on the allelic exclusion process is discussed.

T cell receptor V alpha gene segment with alternate splicing in the junctional region

The locus encoding mouse TCR-alpha chain includes approximately 100 V alpha gene segments that can be organized in about 20 structural subfamilies. Southern blot analysis of a T cell line derived from the BALB/c strain, M5T, has indicated that both alpha loci were rearranged, as assessed by the deletion of the delta locus, and that the V alpha gene segment involved in one of the rearrangements did not belong to any of the V alpha subfamilies already described. Transcripts of TCR-alpha chains from the M5T line were cloned after cDNA synthesis and anchored-polymerase chain reaction, revealing a V alpha gene segment of an as yet unidentified subfamily, V alpha 5T. Molecular cloning of germ-line V alpha 5T gene segments has shown that this subfamily contained two members, one of them being a pseudogene. The two members were located to each extremity of the alpha locus associated with a member of the V alpha 13 and V alpha BWB subfamilies. Analysis of transcripts bearing the V alpha 5T gene segment in the M5T line as well as in thymocytes has revealed that J alpha are frequently absent. This is due to an alternate donor splice site generated at the V alpha 5T-J alpha junction that leads to a splicing from the end of V alpha 5T to C alpha instead of the J alpha to C alpha conventional splicing. The impact of J alpha spliced-out transcripts on the allelic exclusion process is discussed.

Identification of an endogenous mammary tumor virus involved in the clonal deletion of V beta 2 T cells

Expression of V beta (beta-chain variable region) gene segments was investigated in the Mus m. domesticus DDO strain, which possesses a large genomic deletion encompassing 20 of the 29 V beta gene segments known in BALB/c. Stainings using V beta-specific monoclonal antibodies revealed that up to 60% of the peripheral T cells use 3 V beta gene segments. Variable frequencies of V beta 2 T cells were observed among DDO individuals. Segregation analyses of F2 crosses between V beta 2-deletor mice and mammary tumor virus (Mtv)-free mice led to the identification of a new endogenous Mtv, named Mtv-DDO, mediating V beta 2 T cell clonal deletion. Mtv-DDO structure is conserved with the exception of the carboxy-terminal region as compared to other Mtv. Comparison between Mtv sharing the same V beta specificity and isolated from laboratory or wild mice confirms that a stretch of 11 amino acids, defined as the V beta-specific region, is required for the V beta-specific interaction. Limited substitutions in this region account for the shift of the Mtv specificity towards different V beta.

Evidence for antigen driven selection in two monoclonal auto-antibodies derived from nonobese diabetic mice

The nonobese diabetic (NOD) mouse is a model of human type I diabetes. This diabetes is due to massive infiltration of the pancreatic beta cell of islets by autoreactive T cells (insulitis) followed by the destruction of insulin-producing cells. Circulating autoantibodies are also detected, notably against glutamic acid decarboxylase, peripherin and insulin. Two monoclonal autoantibodies directed against insulin and peripherin were obtained by fusing NOD spleen and myeloma cells. We report here the nucleotide sequence of the genes encoding for the V regions of these two antibodies. Somatic mutations were identified by comparing the light chain nucleotide sequence of one of these autoantibodies with its germline counterpart precursor established from NOD mice after PCR gene amplification. The other one displays N additions on both sides of the D region. These results strongly suggest that both autoantibodies have undergone diversification, either N additions or somatic mutations, and therefore present structural features of antibodies derived from animals immunized against exogenous antigens.

Abrogation of H-2-restricted CTL responses and efficient recognition of HLA-A3 molecules in DBA/2 HLA/A24 responder mice

DBA/2 (H-2d) HLA-B7 x human beta 2-microglobulin transgenic and DBA/2 nontransgenic mice stimulated by DBA/2 HLA-A3 x human beta 2-microglobulin transgenic mouse spleen cells developed potent H-2Kd restricted cytolytic responses with recognition of a peptide from the second domain of the HLA-A3 H chain. These H-2Kd-restricted responses obliterated, as a rule, cytolytic responses with direct recognition of the HLA-A3 molecules, even in HLA-B7 transgenic mice. These immunodominant H-2Kd-restricted responses could be abrogated in DBA/2 HLA-A24 mice because of cross-tolerance, the HLA-A3 derived-H-2Kd presented peptide being shared by several (including A24) HLA class I H chain allelic variants. Under such experimental circumstances, strong CTL responses with exclusive direct recognition of HLA-A3 molecules constantly developed. Further analysis of these responses in six DBA/2 HLA-A24 responder mice indicated that a large fraction of the mouse V beta and V alpha genes could be used to mount such CTL responses. Thus, by combining classical HLA class I transgenesis and selective destruction of H-2K and H-2D genes, it should be possible to derive useful strains of mice for the study of HLA class I-restricted CTL responses.

Abrogation of H-2-restricted CTL responses and efficient recognition of HLA-A3 molecules in DBA/2 HLA/A24 responder mice

DBA/2 (H-2d) HLA-B7 x human beta 2-microglobulin transgenic and DBA/2 nontransgenic mice stimulated by DBA/2 HLA-A3 x human beta 2-microglobulin transgenic mouse spleen cells developed potent H-2Kd restricted cytolytic responses with recognition of a peptide from the second domain of the HLA-A3 H chain. These H-2Kd-restricted responses obliterated, as a rule, cytolytic responses with direct recognition of the HLA-A3 molecules, even in HLA-B7 transgenic mice. These immunodominant H-2Kd-restricted responses could be abrogated in DBA/2 HLA-A24 mice because of cross-tolerance, the HLA-A3 derived-H-2Kd presented peptide being shared by several (including A24) HLA class I H chain allelic variants. Under such experimental circumstances, strong CTL responses with exclusive direct recognition of HLA-A3 molecules constantly developed. Further analysis of these responses in six DBA/2 HLA-A24 responder mice indicated that a large fraction of the mouse V beta and V alpha genes could be used to mount such CTL responses. Thus, by combining classical HLA class I transgenesis and selective destruction of H-2K and H-2D genes, it should be possible to derive useful strains of mice for the study of HLA class I-restricted CTL responses.

T-cell receptor identification of an oligodendrocyte-specific autoreactive cytotoxic T-cell clone without self restriction

In addition to myelin basic protein (MBP) and proteolipid protein (PLP), oligodendrocyte (Od) membrane autoantigens, such as the glycoprotein M2/MOG, could participate in the pathogenesis of autoimmune demyelinating diseases of the central nervous system (CNS), such as experimental allergic encephalomyelitis (EAE) or multiple sclerosis (MS). We have described an Od-specific autoreactive and cytotoxic T-cell clone, named C2, which recognized M2/MOG without conventional MHC restriction. In order to analyse the Od/C2 interaction, we determined the alpha/beta T-cell receptor (TCR) variable region usages and structures of C2. Monoclonal antibody stainings of C2 and nucleotide sequences show that the alpha chain is composed of a V alpha 5 and a J alpha identical to J alpha 18BBM142 gene segments, and that the TCR beta chain is composed of V beta 17a, D beta 2.1 and J beta 2.2 gene segments indicating that C2 used a conventional alpha/beta TCR for M2/MOG recognition.

Clonal deletion of V beta 17 T cells in mice from natural populations

In a panel of wild mice trapped in different geographical regions, the concomitant expression of V beta 17 T cell receptors and I-E histocompatibility molecules is frequent. By Southern blot analysis, eight forms of V beta 17 genes have been distinguished that encode five kinds of V beta 17 domains. Populations of Asia display the highest level of polymorphism and include all the V beta 17 forms and domains. The V beta 17 T cells of wild origin are deleted in mice expressing Mls-3 and related superantigens. Wild mice use V beta 17 domains different than the one of laboratory strains. Together with endogenous superantigens polymorphism, this accounts for the observed low frequency of clonal deletion cases in natural populations.

V beta 17 T-cell deletion by endogenous mammary tumor virus in wild-type-derived mouse strain

The wild-type-derived mouse strain PWK possesses a beta-chain variable region V beta 17a2 allele, which is expressed on mature T cells as part of the T-cell receptor of most mice expressing I-E, whereas V beta 17 T cells are deleted in all I-E+ laboratory mice bearing a V beta 17a1 allele. However, (PWK x CBA/J)F1 progeny and the wild-type-derived mouse strain MAI, which possesses the V beta 17a2 allele, display deletion of V beta 17 T cells. Analysis of (PWK x CBA/J) x PWK and of (PWK x MAI) x PWK backcrosses demonstrates that endogenous mouse mammary tumor virus MTV-6 from CBA/J and a MTV from strain MAI control the clonal deletion of V beta 17a2 as well as V beta 3 T cells. Furthermore, among I-E- progeny of a (MAI x C57BL/6) x C57BL/6 backcross, we observed that mice inheriting MTV of MAI have a reduced level of V beta 17 T cells, suggesting that the clonal deletion of V beta 17a2 T cells can be mediated in the absence of the I-E molecule. The 3' long terminal repeat of MTV MAI was cloned and translation of the open reading frame was compared to those of MTV known to encode superantigens. Comparisons indicate that MTV MAI has significantly diverged from the other MTVs. However, MTV MAI and MTV-6 share a stretch of 11 identical amino acids at the C terminus, which is divergent in MTV reacting with other V beta s. This suggests that this region is involved in determining the specificity toward V beta s and has been selectively conserved through evolution of the Mus species.

Linkage of regression and malignant conversion of rabbit viral papillomas to MHC class II genes

Human papillomaviruses associated with cutaneous and anogenital cancers induce intraepithelial precursor lesions which may regress spontaneously or progress into invasive carcinomas. Cell-mediated immune responses are probably involved in regression of precancerous lesions and the polymorphism of the genes responsible may thus have a key role in the variability of the host response. Skin warts and cancers induced in rabbits by Shope papillomavirus provide a model to test this hypothesis. We analysed a restriction-fragment-length polymorphism of major histocompatibility complex class I and class II genes and T-cell receptor beta-chain genes in infected domestic rabbits. We found a strong linkage between wart regression and a DR alpha EcoRI fragment, and an increased relative risk of malignant transformation associated with a DQ alpha PvuII fragment. This indicates a genetic control of wart evolution, involving genes in the class II region of the major histocompatibility complex.

Identification of a T cell receptor beta chain variable region, V beta 20, that is differentially expressed in various strains of mice

A cDNA library of TCR beta chain transcripts from BALB/c thymocytes was constructed using anchored polymerase chain reaction (PCR). Screening of this library led to the identification of a V beta gene segment, V beta 20, structurally related to V beta 3 and V beta 17. Genomic analysis of mice displaying deletions in their V beta loci, together with mapping of cosmid clones, situated V beta 20 2.5 kb beside V beta 17. The expression of V beta 20 was estimated by PCR in mice of different H-2 and Mls types. Peripheral T cells from H-2k and H-2d mice did not express V beta 20, whereas in I-E-negative mice (C57Bl/6 and SJL), V beta 20 transcripts were detected. The lack of V beta 20 transcripts in (C57Bl/6 x CBA/J)F1, (C57Bl/6 x BALB/c)F1, and in congenic B6.H-2k mice suggests that the differential use of V beta 20 is due to an I-E-mediated clonal deletion process. The involvement of the Mls super antigens was excluded by analysis of all Mls type combinations. The nature of the V beta 20-deleting element(s) is discussed in the context of the I-E/superantigen systems controlling the expression of V beta 11 and V beta 17.

Evolution of the rabbit immunoglobulin kappa chain genes

We have analyzed the organization and the structure of rabbit kappa chain genes encoding b allotypes in wild rabbits. The kappa 1 gene of the b95 allotype was cloned and its structure determined. The J region is composed of five segments but only J2 appears to be functional and is identical to the J2 segment of the b4 allotype. The J region is highly conserved among the various b allotypes, whereas the constant region exon displays a high level of differences when compared with other allotypes (9%-30% of different amino acids). The b95 J region is closer to that of b4var and the constant region to b5 allotype constant region. Alignment of nucleotide sequences revealed that the constant region exon displays segmental similarities with b4 and bas constant regions. The mosaic structure of b95 allotype gene indicates that complex allotypes of kappa 1 genes may result from genetic exchanges or gene conversion between the different kappa genes.

Idiotypic replica of an anti-human tumour-associated antigen monoclonal antibody. DNA sequence comparison between Ab1 and Ab3

2G-3 is an anti-anti-idiotypic MoAb (Ab3) obtained upon immunization with a monoclonal Ab2 (A3B10), which behaves as the 'internal image' of CaMBr1, a saccharide epitope defined by MoAb MBr1 (Ab1). CaMBr1 is expressed on glycoconjugates of the human mammary carcinoma cell line MCF-7 and on normal and neoplastic mammary gland epithelial cells. Ab1 and Ab3, although exhibiting, in many respects, superimposable paratopic and idiotopic specificities, show a non-identical fine immunoreactivity, since 2G-3 has a preferential reactivity with the saccharidic epitope mounted on glycoproteins, while MBr1 reacts with both glycoproteins and glycolipids. V-region sequence analysis has shown that: (i) the VK genes employed belong to different families (VK1 and VK10); (ii) the JK2 segment is shared by the two L chains (thus a high degree of homology is observed between VK CDR3s); (iii) the VH genes employed derive from the same family VHIIB/J558 (but show CDR homology only in CDR2); (iv) different JH region genes are employed. These data, together with the comparison of deduced secondary structure parameters, give further evidence for the possible production of similar combining sites using different VH and VL germ-line genes.