Immunologic tolerance: collaboration between antigen and lymphokines

Immunosuppression induced by hepatic portal venous immunization spares reactivity in IL-4 producing T lymphocytes

Immunization of naive or specifically primed C3H/HEJ with irradiated B10.BR spleen cells via the hepatic portal vein leads to an antigen specific decrease in the proliferative and cytotoxic response to B10.BR antigen assayed in vitro (and to increased graft survival of B10.BR grafts in vivo). This effect seems to be mediated in the main by a decrease in IL-2 production from CD4+ T lymphocytes of mice given antigen by the portal route, which is in turn caused by a decreased precursor frequency of IL-2-producing cells. No clear decrease in IL-4 production was seen. Hepatic APC isolated from mice receiving antigen via the portal vein were unable to induce IL-2 production from a C3H/HEJ anti-B10.BR cell line in vitro, in contrast to splenic APC derived from the same mice. Even when antigen was given by conventional (systemic) intravenous routes (in this case via the lateral tail vein) hepatic APC isolated from those mice were unable to stimulate IL-2 production from this cell line. Furthermore, 24 h exposure of a cell line to antigen pulsed hepatic APC left those cells refractory to a subsequent restimulation with antigen presented by splenic APC. Spleen lymphoid cells from primed mice challenged in vivo with B10.BR liver cells (i.v.) were similarly unable to produce IL-2 on rechallenge in vitro with irradiated B10.BR spleen cells, though no defect was seen if in vivo challenge was with B10.BR spleen cells. These data imply that presentation of multiple minor cell surface antigens by hepatic APC leads to specific anergization of IL-2 producing T cells, in a fashion which seems to be distinct from that previously reported as due to 'veto-like' activity.

Clonal analysis of murine B cell response to the human immunodeficiency virus type 1 (HIV1)-gag p17 and p25 antigens

The antigenicity of HIV-gag p17 and p25 proteins was analyzed using a panel of 52 monoclonal antibodies (mAb) derived from 17 independent fusion experiment protocols performed in 12 different laboratories. These mAb were tested for their capacity to bind peptides corresponding to sequences of HIV1-BRU-gag p17 and p25. Thirty-five overlapping peptides (P1 to P35) totally covering the p17 and p25 proteins were used. This study allowed us to identify four immunodominant regions inducing B cell response, two on p17 corresponding to P2 and P13 (amino acids 11-25 and 121-132, respectively) and two on p25 corresponding to P21 and P28-P29-P30 (a.a. 201-218 and 285-320 respectively). According to secondary structure predictions, peptides P2 and P21 contained hydrophilic alpha helix folded regions whereas P13 sequence presented a beta turn propensity. These regions and the P28-30 region were also predicted to be easily accessible to mAb. Several other p25-derived peptides: P15 (a.a. 142-156), P16 (a.a. 148-162), P19 (a.a. 176-192), P22 (a.a. 219-233) and P23 (a.a. 233-253) were recognized by mAb. No p17-derived peptide other than P2, P13 and P12 (a.a. 111-123) was found to react with mAb. Cross-blocking studies between mAb, suggested the existence of more than four distinct epitopic areas on p17 and eight on p25.

Immunologic tolerance in lymphatic filariasis. Diminished parasite-specific T and B lymphocyte precursor frequency in the microfilaremic state

To explore the mechanisms of antigen-specific immune unresponsiveness seen in microfilaremic patients with bancroftian filariasis, T and B cell precursor frequency analysis was performed using PBMC from individuals with either asymptomatic microfilaremia (MF, n = 7) or chronic lymphatic obstruction (CP, n = 20). Highly purified CD3+ cells were partially reconstituted with adherent cells and their proliferative response to parasite antigens determined in cultures of T cells by limiting dilution analysis. A filter immunoplaque assay also assessed the frequency of both total and parasite-specific Ig-producing B cells. While the lymphocyte proliferation to mitogens and to a nonparasite antigen (Streptolysin-O, [SLO]) were similar in all groups of patients, the frequency of parasite-specific CD3+ T cells was significantly lower (geometric mean [GM], 1/3,757) in MF patients when compared to that in CP patients (GM 1/1,513; P less than 0.001). Similarly, the proportion of lymphocytes producing parasite-specific IgE or IgG was significantly lower in MF patients (IgE mean, 0.2%; IgG mean, 0.33%) compared with CP patients (IgE mean, 3.2%; IgG mean, 1.76%; P less than 0.05 for both comparisons). These observations imply that low numbers of parasite-specific T and B lymphocytes may be partially responsible for the severely diminished capacity of lymphocytes from patients with MF to produce parasite-specific antibody and to proliferate to parasite antigen in vitro. Such differences in parasite-specific lymphocyte responses suggest that tolerance by clonal anergy may be a critical mechanism for maintaining the microfilaremic state.

Profound specific suppression by antigen of persistent IgM, IgG, and IgE antibody production

Ongoing, high-titer T-cell-dependent immune responses in adult mice, consisting of IgM, IgG, and IgE anti-fluorescein antibodies, can be specifically and substantially reduced (90-99%) when the mice are injected with appropriate doses of fluoresceinated dextran of defined molecular weight and hapten valence. This suppressive form of the antigen is nontoxic and specific, as responses to other antigens are unaffected. The suppression is long lasting and reduces high-affinity antibodies most markedly. Moreover, plasma cell secretion of specific antibody is virtually eliminated. This demonstrates that the reduction in antibody titer is not simply due to masking of serum antibody by the suppressive polymer. The results are discussed with reference to proposed models of B-cell and T-cell tolerance. Extension of these findings to disease-related immunogens may yield effective antigen-specific treatments of human allergy and autoimmune diseases.

T-cell growth factors and the treatment of patients with cancer

T-cell maturation has traditionally been felt to occur primarily within the thymus but it is now clear that dynamic processes in the periphery govern many functions such as T-cell activation, proliferation, tolerization, and migration into peripheral tissues. Four T-cell growth factors have now been identified. These include: interleukin-2 (IL-2), IL-4, IL-7, and a potent cofactor recently described, IL-10. These factors are believed to work synergistically in the fine regulation of the lymphoid pool. Both IL-2 and IL-4 have entered clinical trials with significant responses in the IL-2-based regimens of up to 40 to 50% in certain tumors. IL-7 and IL-10 are in preclinical studies. Although IL-2, IL-4, and IL-7 have been shown to induce lymphokine-activated killer cell activity from sensitive precursors, such studies have yet to be performed with IL-10.

The majority of cells infected with the defective murine AIDS virus belong to the B-cell lineage

Murine AIDS (MAIDS) is caused by a defective retrovirus which encodes a gag fusion protein (Pr60gag). We previously reported that this virus induced an oligoclonal proliferation of infected cells and suggested that this cell expansion was an important event in the pathogenesis of MAIDS. To identify these target cells, we constructed novel defective viruses whose genomes could be detected with specific probes. Helper-free stocks of these viruses induced MAIDS. Using in situ hybridization and immunocytochemistry and Southern analysis, we found that most infected cells belong to the B-cell lineage. Transformation of these B cells appears to be the primary event responsible for the development of immunodeficiency. This animal model may be relevant to our understanding of AIDS, of the immunodeficiencies associated with B-cell lymphoproliferative disorders, and of the role of B-cell proliferation and transformation in the effects of superantigens, since Pr60gag appears to be a superantigen.

Peripheral deletion of self-reactive B cells

B LYMPHOCYTES are key participants in the immune response because of their specificity, their ability to take up and present antigens to T cells, and their capacity to differentiate into antibody-secreting cells. To limit reactivity to self antigens, autospecific B cells can be functionally inactivated or deleted. Developing B cells that react with membrane antigens expressed in the bone marrow are deleted from the peripheral lymphocyte pool. It is important to ascertain the fate of B cells that recognize membrane autoantigens expressed exclusively on peripheral tissues because B cells in the peripheral lymphoid organs are phenotypically and functionally distinct from bone-marrow B cells. Here we show that in immunoglobulin-transgenic mice, B cells specific for major histocompatibility complex class I antigen can be deleted if they encounter membrane-bound antigen at a post-bone-marrow stage of development. This deletion may be necessary to prevent organ-specific autoimmunity.

Two closely related kappa variable region pseudogenes pose an evolutionary paradox

Two pseudogenes belonging to the Igk-V1 variable region group have been isolated from BALB/c mice. The genes share greater than 96.5% identity of nucleotide sequence in a 1800 base pair (bp) region surrounding the coding region, but deletions of 221 bp and 84 bp have removed essential sequences from the two genes. As the deletions are different in the two pseudogenes, they must have occurred independently in each gene during or subsequent to the duplication event which gave rise to the genes from a common ancestral gene. Polymerase chain reaction analysis was used to identify the pseudogenes in inbred strains of mice. BALB/c (Igkc) and AKR (Igka), prototype strains representative of the predominant kappa haplotypes, possess both pseudogenes but no intact copy. Only one of the pseudogenes was present in SJL (Igka). Strains C58, c.C58 (Igkd) and NZB (Igkb) possessed an intact version of the gene. This distribution of haplotypes is consistent with a close linkage of the pseudogenes with other Igk-V1 genes on chromosome 6. The translated amino acid sequence of the pseudogenes indicates that prior to their acquiring deletions they encoded typical Igk-V1 variable regions except for an unusual FR2 region, in which the conserved proline at position 44 is replaced by leucine and the normally hydrophobic position 36 was occupied by histidine. Possible mechanisms to explain the occurrence of deletions in both of the pseudogenes in the recent evolution of BALB/c are discussed. One explanation would be that the two genes were already nonfunctional at the time of the duplication so that the subsequent deletions represent neutral events which became fixed in the inbred strains by a process of genetic drift. Alternatively, if the genes were functional at the time of duplication, their rapid loss due to deletion events suggests that negative selection may have acted to eliminate the genes from the V-region repertoire.

Autoimmune response induction and regulation in rat erythrocyte-immunized mice

The process of antibody formation to self-red blood cells (RBC) has been studied in rat RBC (rRBC)-immunized mice. A positive correlation was noted between antibody production to mouse RBC (mRBC) and rRBC in some mouse strains. The low responsiveness on both indices was overcome by s.c. injections of rRBC in low doses. rRBC-tolerant mice exhibited lower levels of antibody production to mRBC. Splenocytes from rRBC-immunized donors, when transferred to irradiated recipients, revealed enhanced and accelerated anti-mRBC and anti-rRBC antibody production in response to rRBC but not to autologous mRBC. Consequently, the autoimmune process is not accompanied by disordered immunologic tolerance to self-RBC and requires participation of Th responding to foreign epitopes of rRBC antigens. Splenocytes from rRBC-immunized donors, when transferred to non-irradiated recipients, inhibited antibody production to mRBC. The suppressive effect was not abrogated by pretreating donors or recipients with low doses of cyclophosphamide (CP) or by pretreating donors with antibodies to I-J. It was abrogated by the elimination of cells of donor origin within 8-9 days after transfer. Inoculation of antibodies to rRBC in immunized mice on a schedule imitating their splenocyte transfer dynamics inhibited antibody production to mRBC. Therefore, it can be assumed that the suppressive effect of cell transfer is accounted for, not by suppressors or their inducers, but by antibodies to rRBC on the basis of feedback regulation.

Transgenic regulation in laboratory animals

This chapter is an attempt to summarize some commonly accepted and some more subjective opinions about the regulation of transgene expression in laboratory animals. After a short historical introduction, I present some general notions regarding gene structure/function. The spotlight shifts then to the description of the most popular techniques for gene transfer, including the targeted gene replacement. The different approaches are briefly discussed in terms of intrinsic advantages and limitations regarding gene expression patterns. Furthermore, the role of enhancers, promoters and other cis-acting elements such as silencers and dominant control regions as well as their involvement in the chromatin on-off state are discussed on the basis of a specific example studied in our laboratory. The review concludes by presenting recent results and the new perspectives opening in the field of 'surrogate' (also called 'reversed') genetics. Some problems which remain to be solved both at the technical as well as at the social-ethical level are also briefly presented.

Cytokines in viral diseases

As in many other areas of cytokine biology, recent studies of the role of cytokines in viral disease reveal numerous complex interactions that in many instances may contribute directly to the development of pathology. For example, data from the rapidly evolving field of human retrovirology has shown that these viruses, as well as inducing the expression of many cellular cytokine genes, can be activated from latency and driven into replication/expression by the very same cytokines. The continuing rapid expansion of knowledge in the cytokine area augers well for eventual development of novel antiviral therapeutic strategies based on manipulation of the cytokine network.

The immune-hypothalamo-pituitary-adrenal axis and autoimmunity

Immunoendocrinology is a rapidly expanding field, uncovering numerous bilateral interactions between the immune system and neuroendocrine circuits. Various hormones and neurotransmitters appear to modulate cells of the immune system and likewise cytokines control the function of neuroendocrine system. In the present paper, we discuss some lines of evidence indicating that an immunoendocrine feedback loop, which we term 'immune-hypothalamo-pituitary-adrenal system' is an integral part of the regulation of self tolerance. The finding that pathology of this immunoendocrine feedback loop is related to development of autoimmunity may lead to new prophylactic and therapeutic strategies.

Immunotherapy of cancer with lymphokines and lymphokine-activated killer cells

Our expanding knowledge of the immune system has provided a basis of rationality for immunotherapy. Some non-specific immunotherapy has achieved the status of standard treatment: interferon in hairy cell leukemia and chronic myelogenous leukemia, BCG in bladder cancer, and levamisole in colon cancer adjuvant therapy. Tumor infiltrating lymphocytes, moreover, offer a level of specificity heretofore unknown. Combined with the newly available synthetic cytokines that regulate the normal immune system there is the potential for a major breakthrough in biotherapeutics. Problems remain. We have yet to identify tumor antigens with the precision necessary for effective immunotherapy. Indeed, we have no assurance that tumors will regularly synthesize new antigens. In the broad spectrum of immune deficiency syndromes, we have yet to see an increase in the common epithelial tumors that account for the great bulk of human cancer. This suggests that we still have a great deal more to learn.

Comparison of the humoral and cytotoxic T-lymphocyte response to individual HLA class I alloantigens in highly immunized patients

In order to investigate the correlation between activation of cytotoxic T-lymphocyte precursor (CTLp) and the formation of antibodies to alloantigens, we studied 21 highly sensitized patients waiting for a kidney transplantation. Both antibody reactivity and CTLp frequencies of these patients were determined against 88 individual HLA class I alloantigens. A high or low CTLp frequency against a certain HLA-A or -B alloantigen was not correlated with the presence or absence of the antibodies to that antigen. Mismatched antigens, towards which the patient had not formed antibodies, can induce either a higher or a lower frequency of CTLp compared to mismatches towards which the patients had formed antibodies. The possible implications of this lack of correlation between the T- and B-cell allorepertoires with regard to donor selection for (highly immunized) patients is discussed.

Splenic and granuloma T-lymphocyte responses to fractionated soluble egg antigens of Schistosoma mansoni-infected mice

Soluble egg antigens (SEA) secreted by the eggs of Schistosoma mansoni worms induce a T-cell-mediated granulomatous response that is principally responsible for the pathology of the disease. In the present study sodium dodecyl sulfate-polyacrylamide gel electrophoresis-separated SEA proteins were divided into nine fractions (less than 21, 25 to 30, 32 to 38, 40 to 46, 50 to 56, 60 to 66, 70 to 90, 93 to 125, and greater than 200 kDa), electroeluted, and utilized in in vitro lymphoproliferation assays. T-cell-enriched spleen cells from acutely infected mice responded to all nine fractions, while those from chronically infected mice responded to only the 50- to 56- and the 60- to 66-kDa fractions. Depletion of the CD4+ T-cell subset among acute and chronic-infection spleen cells abrogated the response. Depletion of the CD8+ T-cell population resulted in increased proliferation in response to fractions by acute-infection T cells and facilitated responsiveness to hitherto-inactive SEA fractions in chronic-infection T cells. Acute-infection CD4+ granuloma T cells responded to the 40- to 46-, 50- to 56-, 70- to 90-, 93- to 125-, and greater than 200-kDa fractions, while the chronic-infection granuloma T cells responded only to the greater than 200-kDa fraction of SEA. Selective depletion of the CD4+ T-cell subset when acute-infection granuloma lymphocytes were tested abrogated proliferation, whereas subset depletions when chronic-infection granuloma cells were tested indicated that both CD4+ and CD8+ T cells respond to the greater than 200-kDa fraction. The present study reveals differences between acute- and chronic-infection splenic and granuloma T cells in the pattern of T-cell blastogenic responses to fractionated SEA.

Cytokine gene expression: analysis using northern blotting, polymerase chain reaction and in situ hybridization

We describe here the use of northern blotting, PCR and in situ hybridization for the analysis of cytokine gene expression. These techniques, each with their advantages and disadvantages, have been used to monitor cytokine gene expression in sites of immune reactivity and in the developing thymus. Whilst expression of a gene usually correlates well with protein production from that gene, this may not always be the case. The development of methods to analyze protein production in situ, for instance by immunohistochemistry, together with analysis of mRNA expression will allow us to begin to understand the role of cytokines within the immune system of the intact animal.

Expression of anti-DNA immunoglobulin transgenes in non-autoimmune mice

Self-reactive B cells can be regulated by either deletion or inactivation. These manifestations of self-tolerance have been dramatically shown in transgenic mice in which the number of self-reactive cells has been artificially expanded. We have now extended these models to ask if B-cell tolerance as described for non-disease-associated antigens also operates for the targets of autoimmunity. The target we have chosen is DNA. Anti-DNA antibodies are diagnostic of certain autoimmune syndromes in humans and are a characteristic of the murine model of systemic autoimmunity, the MRl/lpr mouse. Antibodies to both single-stranded and double-stranded DNA have been implicated in disease. By generating anti-DNA transgenic mice, we have addressed the question of whether DNA-specific B cells are regulated in normal (non-autoimmune) mice. We indeed found that most transgenic B cells bind DNA, yet we failed to detect secreted anti-DNA. We suggest that as a consequence of their self-reactivity these B cells are developmentally arrested.

Peripheral tolerance to alloantigen results from altered regulation of the interleukin 2 pathway

Tolerance to alloantigen may be induced in rats by administration of blood followed by transplantation of a renal allograft. The mechanism of this tolerance was investigated by directly analyzing the functional activity of graft-infiltrating cells. We have previously shown cytotoxic T lymphocyte infiltration of, and major histocompatibility complex induction on, grafts of tolerant animals. We now report that cells isolated from the grafts of tolerant rats show a reduced expression of the p55 interleukin 2 receptor (IL-2R) chain on the cell surface compared with that seen on the cells of untreated animals. Scatchard analysis further reveals low expression of high affinity IL-2R. This is due to reduced transcription of both IL-2R alpha and beta chain mRNAs and results in a reduced ability of cells to proliferate in response to IL-2. Cells isolated from tolerant animals are unable to make biologically active IL-2 in culture, whereas cells from untreated animals make high levels. This is not reflected at the mRNA level as the IL-2 gene is induced in both tolerant and untreated animals to similar levels. The induction of tolerance is abrogated by administration of recombinant IL-2 to animals at the time of transplantation. Thus, we conclude that an altered regulation of the IL-2 pathway results in tolerance in these alloantigen-treated and transplanted animals.

A role for CD8+ T lymphocytes in the pathogenesis of AIDS

Experimental and clinical evidence is presented which supports the hypothesis that CD8+ T lymphocytes aimed at suppressing HIV replication in infected CD4+ T cells may have an important role in the pathogenesis of AIDS by directly causing a decrease in CD4+ T lymphocyte numbers. Possible models to test this hypothesis are discussed.

What roles have anti-interferon antibodies in physiology and pathology?

Until recently the generation of antibodies to interferons (IFNs) was considered an unlikely event, while it is now clear that natural interferons (except IFN-beta) are practically nonimmunogenic, although recombinant interferons give rise to antibodies in about 30% of patients with occasional clinical complications. By realizing that normal individuals display spontaneously traces of IFN autoantibodies, in this review it is suggested that (if immunotherapy has to succeed) new generations of recombinant proteins should be the least antigenic as possible.

The role of thymic epithelium in the acquisition of tolerance

There are two separate mechanisms of induction of T-cell tolerance in the thymus. First, MHC molecules expressed on bone-marrow-derived cells can cause clonal deletion of autoreactive cells. Second, as discussed here by Elisabeth Houssaint and Martin Flajnik, thymic epithelial cells can generate a form of tolerance that does not eliminate self-reactive clones. This nondeletional mechanism, which is also a feature of the other MHC class-II-bearing epithelia, may contribute to the establishment of tolerance-maintaining regulatory networks.

T-cell clones that react against autologous human tumors

T cells (derived from peripheral blood lymphocytes [PBL], lymph nodes or tumor tissues and restimulated with autologous tumor cells and expanded in interleukin-2 [IL-2]), when cloned, produce three functional classes of clone. Class I T-cell clones exhibit the phenotype of alpha/beta cytotoxic T lymphocytes (CD3+, CD8+, CD4-, WT31+), use their CD3-alpha/beta complexes for cognate function, and lyse the autologous tumor cells specifically in a major histocompatibility complex (MHC) Class I-restricted manner. The second class of T cell clone expresses identical phenotype but exhibits a rather broad cytotoxic profile against the autologous and allogeneic tumor cells derived from tumors with similar and/or dissimilar histologies. Although these CTL clones can, at times, show MHC Class I-restricted killing and use their T-cell receptors (TCR) complexes for function, activation via certain accessory molecules, particularly lymphocyte-function associated (LFA-1) antigens, might induce their broad cytotoxic behavior. The nature of the tumor antigen recognized by the Class I antigen-specific CTL clones remains unknown. It is evident, however, that more than one antigen can be associated with a given tumor and they are recognized by different CTL clones from individual patients. The third class of T-cell clone is usually of CD4+ alpha/beta T cells (CD3+, CD4+, CD8-, WT31) and these T-cell clones exhibit no cytotoxicity toward the autologous or allogeneic target cells. When tested for potential regulatory property, one type of CD4+ T-cell clone exhibits the characteristics of helper T cells. This type induces or amplifies cytotoxic response in fresh PBL by elaborating interleukin-2 (IL-2) and interferon-gamma). These helper T-cell clones can proliferate against the autologous tumor cells and demonstrate functional specificity for the autologous tumor cells. The other type of CD4+ T-cell clone exhibits the phenotype of the helper T-cell clone (CD3+, CD4+, CD8-, WT31+) but suppresses the cytotoxic response of the autologous PBL in co-culture in the presence of the autologous tumor cells and exogenous IL-2. In some situations, these CD4+ suppressor T-cell clones exhibit considerable specificity for the autologous tumor cells. They do not suppress the cytotoxic response against allogeneic targets or against EBV-infected autologous lymphoblastoid cells. Furthermore, they specifically up-regulate their IL-2 receptors (IL-2R) when stimulated by the autologous tumor cells or with autologous tumor cell-pulsed antigen-presenting cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Lack of T-cell tolerance of noninherited maternal HLA antigens in normal humans

Recent clinical reports of nonresponsiveness to noninherited maternal human leukocyte antigens have led to speculation that humans may acquire tolerance of noninherited maternal antigens through exposure to maternal cells neonatally or in utero. To test this hypothesis, we measured the responsiveness of normal subjects to their noninherited maternal and paternal antigens using cell-mediated lympholysis assays and mixed leukocyte reactions. All individuals exhibited cell-mediated lympholysis and mixed leukocyte reaction responses to the maternal cells that were comparable to those to the paternal cells. Limiting dilution analyses revealed significant cytotoxic T-lymphocyte precursor frequencies to both sets of parental antigens. To exclude the possibility that tolerance of individual noninherited maternal antigens was masked by the response to other antigens expressed on the same target cell, we raised cytotoxic T lymphocytes to the maternal cells and then tested for reactivity to a panel of targets that expressed single noninherited maternal HLA antigens. In all cases, each noninherited maternal antigen expressed on the maternal cells elicited a significant cell-mediated lympholysis response. An analysis of clinical data showed that pretransplant mixed lymphocyte reactions to maternal cells are not significantly lower than those to paternal cells. These data suggest that the reported B-cell tolerance of noninherited maternal antigens is not mediated by clonal deletion of T cells induced by exposure to the maternal cells neonatally or in utero.

The influence of allogeneic cells on the human T and B cell repertoire

Clinical transplantation is often complicated by rejection episodes, in which the immune system of the recipient reacts to the foreign transplantation (HLA) antigens on the graft. This immune response includes humoral and cellular components. In the first, B lymphocytes form antibodies to the HLA alloantigens. In the second, CD8+ T lymphocytes recognize and react to HLA class I antigens, and CD4+ T cells react to HLA class II antigens. The frequency and severity of these rejection episodes can be diminished by immunosuppressive drugs, HLA matching between donor and recipient, and immune modulation by blood transfusion. Effective HLA matching between donor and recipient is not always possible and often not necessary. Insight into the factors that influence the T and B cell repertoire after blood transfusion might lead to new approaches to improve graft survival.

Anti-immunoglobulins induce death by apoptosis in WEHI-231 B lymphoma cells

Anti-membrane immunoglobulin (anti-mIg) antibodies exert inhibitory effects in immature B lymphocytes such as WEHI-231 cells. We show here that anti-mIg treatment causes DNA fragmentation (apoptosis) in these cells. We also report that co-treatment with the protein kinase C activator phorbol 12-myristate 13-acetate prevents apoptosis induced by anti-mIg. These results are in agreement with our initial proposal that sensitivity to the toxic effects of anti-mIg reflects, at least partially, altered signal transduction in immature B lymphocytes. Variations in signal transduction pathways during B lymphocyte ontogeny may, therefore, play a critical role in determining whether B cells should be activated or inhibited via their mIg.

Lymphokine gene therapy for cancer

The plethora of recombinant lymphokines that have recently become available has led to renewed hope for an immunotherapeutic solution to cancer. Many lymphokines, either singly or in combination, have already shown promise in animal trials and in preliminary human trials. Systemic lymphokine toxicity has been the major constraint on this type of therapy, often precluding the use of doses sufficient to induce tumour regression. To realize the therapeutic potential of recombinant lymphokines against cancer, alternative modes of delivery are needed which maximally stimulate local anti-tumour responses whilst causing minimal systemic toxicity. In this article, Stephen Russell proposes that tumour cell targeted lymphokine gene therapy would optimize lymphokine delivery. Some of the practical difficulties likely to be encountered with such an approach are also discussed.

Virus-induced autoantibody response to a transgenic viral antigen

The induction of autoantibodies and their possible role in the pathogenesis of autoimmune disease are poorly understood. Involvement of infectious agents has been suspected, but direct evidence is sparse. Whether immunological unresponsiveness to self by antibody-forming B cells is maintained by clonal abortion, clonal anergy or suppression, or how the scenario of interactions between helper T cells, B cells and antigen-presenting cells is distorted in autoantibody responses, is being analysed and widely debated. To evaluate tolerance of neutralizing B-cell responses we used transgenic mice expressing the cell membrane associated glycoprotein (G) of vesicular stomatitis virus (VSV) as self-antigen. We show that autoantibodies to VSV-G cannot be induced by VSV-G in adjuvant or by recombinant vaccinia virus expressing VSV-G, but are triggered by infection with wild-type VSV. The data show that helper T-cell tolerance is crucial in maintenance of B-cell non-reactivity and that cognate T-B recognition is necessary to break tolerance of self-reactive B cells. These results may help to understand mechanisms of virus-induced autoimmunity.

Epstein Barr virus transformation of peripheral blood B cells secreting antibodies reactive with cell surface antigens

EBV transformable peripheral blood B cells secreting antibodies reactive with cell surface antigens present on two indicator human leukemia cell lines, NALM1 and U937, were studied. Oligoclonal EBV transformants from patients with a variety of diseases were frequently found to produce cell surface reactive antibodies. Antibody secreting transformants could also, although less frequently, be readily cultured from the PBM of normal volunteers, and represented, by limiting dilution, 1 out of 113 transformable B cells. CD8 antibody had no effect on the frequency of antibody producing B cells, but depletion of CD8+ cells by immunomagnetic methods prior to transformation significantly (P less than 0.05) increased the recovery of antibody secreting B cells to 1/33. Readdition of magnetically depleted cells did not significantly inhibit the transformation of these B cells. During the acute and recovery phases of some infections increasing numbers of these transformable antibody producing B cells appear in the circulation. The majority of antibodies produced were of the IgM class, although IgG antibodies were also detected. IgM antibody producing transformants were tested and some were found to react with autologous and allogeneic normal lymphocytes. These results lend support to the notion that B cells capable of secreting cell surface reactive antibodies, a proportion of which are autoreactive, are present in the normal repertoire of healthy adults, and that these cells are under active regulation by CD8+ cells.

How some T cells escape tolerance induction

A feature common to many animal models of autoimmune disease, for example, experimental allergic encephalomyelitis, experimental autoimmune myasthenia gravis and collagen-induced arthritis, is the presence of self-reactive T cells in healthy animals, which are activated to produce disease by immunization with exogenous antigen. It is unclear why these T cells are not deleted during ontogeny in the thymus and, having escaped tolerance induction, why they are not spontaneously activated by self-antigen. To investigate these questions, we have examined an experimental model in which mice are tolerant to an antigen despite the presence of antigen-reactive T cells. We find that the T cells that escape tolerance induction are specific for minor determinants on the antigen. We propose that these T cells evade tolerance induction because some minor determinants are only available in relatively low amounts after in vivo processing of the whole antigen. For the same reason, these T cells are not normally activated but can be stimulated under special circumstances to circumvent tolerance.

CD40 Ligand Rescues Inhibitor of Differentiation 3-Mediated G1Arrest Induced by Anti-IgM in WEHI-231 B Lymphoma Cells

The engagement of membrane-bound Igs (mIgs) results in growth arrest, accompanied by apoptosis, in the WEHI-231 murine B lymphoma cells, a cell line model representative of primary immature B cells. Inhibitor of differentiation (Id) proteins, members of the helix-loop-helix protein family, functions in proliferation, differentiation, and apoptosis in a variety of cell types. In this study, we analyzed the involvement of Id protein in mIg-induced growth arrest and apoptosis in WEHI-231 cells. Following stimulation with anti-IgM, expression of Id3 was up-regulated at both the mRNA and protein levels; this up-regulation could be reversed by CD40L treatment. Retrovirus-mediated transduction of the Id3 gene into WEHI-231 cells resulted in an accumulation of the cells in G1phase, but did not induce apoptosis. E box-binding activity decreased in response to anti-IgM administration, but increased after stimulation with either CD40L alone or anti-IgM plus CD40L, suggesting that E box-binding activity correlates with cell cycle progression. WEHI-231 cells overexpressing Id3 accumulated in G1phase, which was accompanied by reduced levels of cyclin D2, cyclin E, and cyclin A, and a reciprocal up-regulation of p27Kip1. Both the helix-loop-helix and the C-terminal regions of Id3 were required for growth-suppressive activity. These data suggest that Id3 mimics mIg-mediated G1arrest in WEHI-231 cells.