Construction and properties of new Lyt-congenic strains and anti-Lyt-2.2 and anti-Lyt-3.1 monoclonal antibodies

Graft survival and cytokine production profile after limbal transplantation in the experimental mouse model

Limbal transplantation or limbal stem cell (LSC) transfer represents the only way to treat severe ocular surface damage or LSC deficiency. However, limbal allografts are promptly rejected in spite of extensive immunosuppressive therapy. To characterize immune response after limbal transplantation, we established an experimental model of limbal transplantation in the mouse. Syngeneic, allogeneic and xenogeneic (rat) limbal grafts were grafted orthotopically in BALB/c mice and graft survival was evaluated. The presence of graft donor cells and the expression of IL-2, IL-4, IL-10, IFN-γ and inducible nitric oxide synthase (iNOS) mRNA in the grafts were detected by real-time PCR. While syngeneic grafts survived permanently, allografts were rejected in 9.0±1.8 days and xenografts in 6.5±1.1 days. The manifestation of clinical symptoms of rejection correlated with the disappearance of donor cells in the graft and in the recipient cornea. Intragraft expression of iNOS mRNA and distinct expression patterns of Th1 (IL-2, IFN-γ) and Th2 (IL-4, IL-10) cytokines were detected during rejection of limbal allografts and xenografts. The limbal graft rejection was prevented with anti-CD4, but not anti-CD8 monoclonal antibody therapy. The results indicate that limbal grafts do not enjoy immune privilege of the eye and are promptly rejected by Th1 (allografts) or by a combined Th1 and Th2 (xenografts) type of immune response involving CD4+ cells and iNOS expression. Targeting this pathway may be an effective way to prevent and treat limbal graft rejection.

Corneal rat-to-mouse xenotransplantation and the effects of anti-CD4 or anti-CD8 treatment on cytokine and nitric oxide production

Corneal xenotransplantation may be an alternative approach to overcome shortage of allografts for clinical transplantation. Orthotopic corneal rat-to-mouse xenotransplantation and syngeneic transplantation was performed and the effects of anti-CD4 and anti-CD8 treatments on corneal xenograft survival and production of cytokines, interleukin (IL)-2, IL-4, IL-10, gamma-interferon (IFN-gamma) and nitric oxide (NO) were evaluated. RT-PCR was used to determine the expression of genes for cytokines and inducible nitric oxide synthase (iNOS) in the grafts. The presence of iNOS protein in grafts was detected by immunofluorescent staining. We found that corneal xenotransplantation was associated with a strong upregulation of genes for both Th1 and Th2 cytokines and with NO production in the graft. Treatment of xenograft recipients with mAb anti-CD4, but not anti-CD8, resulted in a profound inhibition of IL-2, IL-4 and IL-10 production, and in a significant prolongation of corneal xenograft survival. The results show that upregulation of Th2 cytokines after corneal xenotransplantation does not correlate with xenograft rejection. Rather, corneal graft rejection is associated with the expression of genes for IFN-gamma and iNOS and with NO production.

Prevention of corneal allograft rejection in a mouse model of high risk recipients

AIM

To determine the effectiveness of treatment with immunosuppressive drugs and monoclonal antibodies (mAb) after penetrating keratoplasty in two different models of high risk mouse recipients.

METHODS

Corneas were grafted orthotopically in mouse models of high risk recipients with either neovascularisation of the graft bed or presensitisation to graft donor antigens. Recipients were treated with mAb against CD4(+) or CD8(+) cells or against T cells, or were treated with cyclosporin A (CsA) or mycophenolate mofetil (MMF), or a combination of both drugs.

RESULTS

Control untreated recipients with neovascularised graft bed or presensitised to the graft donor antigens rejected corneal allografts in 12.5 (SD 2.3) and 9.9 (1.6) days, respectively. Treatment of graft recipients with a neovascularised graft bed with mAb anti-CD4 or anti-T cells, but not with mAb anti-CD8 or with immunosuppressive drugs, resulted in a significant prolongation of graft survival; 75% and 28.5%, respectively, of grafts survived for more than 45 days after grafting. However, none of the treatments were successful in presensitised recipients.

CONCLUSIONS

Treatment of high risk recipients with mAb anti-CD4 is more effective in preventing corneal allograft rejection than the treatment with mAb anti-CD8 or the immunosuppressive drugs MMF and CsA. However, the effectiveness of the treatment depends on the recipients' pretransplantation risk type.

Nitric oxide as a regulatory and effector molecule in the immune system

Nitric oxide (NO) as a small ubiquitous molecule influencing a great variety of biological processes in the organism. Within the immune system, increased levels of NO were observed in various immunopathological situations, inflammatory reactions and during the response to transplantation and tumour antigens. It appears that NO can influence various facets of immune response. We studied involvement and the role of NO in immune response to skin allograft in mice. The production of NO at the site of graft rejection correlated well with the kinetic of rejection reaction and with the fate of the allograft. Graft infiltrating macrophages were identified as a principal cell population producing NO and the production of NO by macrophages was dependent on the presence of activated CD4(+) T cells. Survival of skin allografts was significantly prolonged by the treatment of graft recipients with 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of inducible NO synthase (iNOS). These results suggest a role for NO as the effector cytotoxic molecule involved in the graft rejection. Experiments in vitro demonstrated that NO, in addition to its effector function, acts as a modulator of cytokine production. Spleen cells stimulated with alloantigens in the presence of AMT or S-ethylisothiourea (EIT), an another selective iNOS inhibitor, produced considerably more interleukin (IL)-4 and IL-10 than the cells stimulated in the absence of iNOS inhibitors. The production of Th1 cytokines IL-2 and interferon (IFN)-gamma was not enhanced by the inhibition of NO synthesis. The results altogether show that NO can act in transplantation reactions as an immunomodulator on cytokine production level and as an effector molecule involved in the graft destruction.

Alloantigen-induced, T-cell-dependent production of nitric oxide by macrophages infiltrating skin allografts in mice

The immunological rejection reaction occurring after organ or tissue transplantation is characterized by a strong infiltration of the graft by T cells and macrophages. Since the rejection reaction is highly specific, we tested the role of T cells in the activation of macrophages and in the induction of nitric oxide (NO) production during graft rejection. The rejection of both MHC and non-MHC antigen-disparate skin allografts was associated with a significantly increased production of NO in the graft. The kinetics of NO production after transplantation correlated with the rejection reaction and with the fate of the allograft. A significant reduction in NO production was found in immunologically hyporeactive mice treated with cyclosporine, and no specific production of NO was found in tolerated skin allografts from neonatally tolerant mice. The production of NO was completely suppressed in graft explants from mice with depleted CD4(+) cells, but remained at a normal level in skin allografts from mice treated with anti-CD8 monoclonal antibody. The treatment of recipients of fully allogeneic skin grafts with 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of the inducible NO synthase, resulted in a significant prolongation of graft survival. The results thus show CD4(+) T-cell-dependent, alloantigen-induced production of NO by graft-infiltrating macrophages and the role of NO in the rejection reaction. We suggest that this pathway may represent one of the local effector mechanisms of graft rejection.

Exclusive Th2 primary effector function in spleens but mixed Th1/Th2 function in lymph nodes of murine neonates

Recent studies have shown that neonatal mice are competent to develop mature, Ag-specific Th1 function in situ. However, under many conditions, Th2 responses dominate in the neonate, while Th1 responses are more prevalent in adults. To compare further the immune responses of neonates and adults, we used the enzyme-linked immunospot method to measure the frequencies of primary Th1/Th2 effectors generated in situ in the spleens and lymph nodes. As assessed by the detection of IFN-gamma- or IL-4-producing cells, adults developed mixed Th1/Th2 responses in both organs. Neonatal lymph nodes contained mature frequencies of IFN-gamma- and IL-4-producing cells. In striking contrast, while mature frequencies of Th2 cells developed in neonatal spleens, virtually no IFN-gamma-secreting cells were detected. Exclusive Th2 function was observed in both BALB/c and C57BL/6 neonates, strains in which the Th2 and Th1 lineages, respectively, are favored in adults. Although Th1 effectors were virtually undetectable, the addition of rIL-12 boosted the frequency of IFN-gamma-secreting cells to adult levels. Therefore, Th1 effectors apparently developed in situ, but Th1 effector function either was not promoted or was inhibited upon subsequent exposure to the Ag in culture. Together, these results indicate that the quality of a primary Th response in neonates is strongly dependent on the site of initial Ag exposure; responses initiated in the lymph nodes are mixed Th1/Th2, whereas responses occurring in the spleen are heavily Th2 biased.

The Role of CD8α′ in the CD4 Versus CD8 Lineage Choice

During thymic development the recognition of MHC proteins by developing thymocytes influences their lineage commitment, such that recognition of class I MHC leads to CD8 T cell development, whereas recognition of class II MHC leads to CD4 T cell development. The coreceptors CD8 and CD4 may contribute to these different outcomes through interactions with class I and class II MHC, respectively, and through interactions with the tyrosine kinase p56lck (Lck) via their cytoplasmic domains. In this paper we provide evidence that an alternatively spliced form of CD8 that cannot interact with Lck (CD8α′) can influence the CD4 vs CD8 lineage decision. Constitutive expression of a CD8 minigene transgene that encodes both CD8α and CD8α′ restores CD8 T cell development in CD8α mutant mice, but fails to permit the development of mismatched CD4 T cells bearing class I-specific TCRs. These results indicate that CD8α′ favors the development of CD8-lineage T cells, perhaps by reducing Lck activity upon class I MHC recognition in the thymus.

Tolerance to Antigen-Presenting Cell-Depleted Islet Allografts Is CD4 T Cell Dependent

Pretreatment of pancreatic islets in 95% oxygen culture depletes graft-associated APCs and leads to indefinite allograft acceptance in immunocompetent recipients. As such, the APC-depleted allograft represents a model of peripheral alloantigen presentation in the absence of donor-derived costimulation. Over time, a state of donor-specific tolerance develops in which recipients are resistant to donor APC-induced graft rejection. Thus, persistence of the graft is sufficient to induce tolerance independent of other immune interventions. Donor-specific tolerance could be adoptively transferred to immune-deficient SCID recipient mice transplanted with fresh immunogenic islet allografts, indicating that the original recipient was not simply “ignorant” of donor antigens. Interestingly, despite the fact that the original islet allograft presented only MHC class I alloantigens, CD8+ T cells obtained from tolerant animals readily collaborated with naive CD4+ T cells to reject donor-type islet grafts. Conversely, tolerant CD4+ T cells failed to collaborate effectively with naive CD8+ T cells for the rejection of donor-type grafts. In conclusion, the MHC class I+, II− islet allograft paradoxically leads to a change in the donor-reactive CD4 T cell subset and not in the CD8 subset. We hypothesize that the tolerant state is not due to direct class I alloantigen presentation to CD8 T cells but, rather, occurs via the indirect pathway of donor Ag presentation to CD4 T cells in the context of host MHC class II molecules.

Enhanced murine CD4+ T cell responses induced by the CD2 ligand CD48

The physiological functions of murine CD2 and its ligand CD48 are uncertain. We have examined the role of the CD2-CD48 interaction in murine T cell activation using a series of Chinese hamster ovary (CHO) cell transfectants. CHO cells expressing I-Ad together with CD48 induced more potent activation of OVA-specific, I-Ad-restricted DO11.10-transgenic T cells than CHO cells expressing I-Ad alone. CD48 augmented proliferation and IL-2 production in response to antigen. The enhancing effect of CD48 was of the same magnitude as that seen for CD80 (B7-1). Conjugate assays revealed the ability of CD48 to increase adhesion between T cells and CHO transfectants. The enhancing effects of CD48 on T cell-antigen-presenting cell adhesion and T cell activation were inhibited by anti-CD2 monoclonal antibody. This report provides the first evidence that the CD2 ligand CD48 contributes to the interactions of murine CD4+ T cells with antigen-presenting cells.

Effect of mild chronic stress, as a model of depression, on the immunoreactivity of C57BL/6 mice

Numerous studies correlate the state of depression with some abnormalities in the immune response, such as increased numbers of white blood-cells, alterations in sub-populations of leucocytes, suppression of cytotoxic activity of natural-killer cells, increased levels of some autoantibodies and acute-phase proteins. Some of these changes have been attributed to autoimmunological reactions. While the possibilities to evaluate some reactions in depressed patients are limited, an animal model of depression could well simulate this clinical situation, and the chronic mild state of stress is a well accepted one. After undergoing stress for three-weeks, C57BL/6 mice demonstrate in the present study a decrease in thymus weight, as well as increased interleukin-1 and decreased interleukin-2 production. Splenocytes of the depressed mice exert a decrease in natural-killer-cell activity, in the proliferative response to Concanavalin-A, interleukin-1 and anti-CD3 monoclonal antibodies and an increase in the proliferative response to lipopolysaccharides and pokeweed mitogens. Our results also suggest that chronic stress-induced activation of suppressor cells in the spleen, due to elimination of CD8+ cells, increase the proliferation of splenocytes in response to mitogens of T cells.

Urocanic Acid Enhances IL-10 Production in Activated CD4+ T Cells

The immunosuppressive effects of UV radiation have been well documented. This suppression has been attributed to the action of the cis form of urocanic acid (UCA), a photoproduct of trans-UCA, a natural constituent of the skin. Here, we show that mouse spleen cells preincubated with cis-UCA have a diminished proliferative response to allogeneic cells in MLC and to stimulation with anti-CD3 mAb. Cells preincubated with cis-UCA also had a decreased ability to serve as APC and to stimulate the proliferation of allogeneic lymphocytes in MLC. Simultaneously, the production of IL-2 and IFN-γ by cells preincubated with cis-UCA was decreased. However, IL-10 gene expression and IL-10 protein secretion by spleen cells stimulated in the presence of cis-UCA were significantly enhanced. The principal cell population displaying the cis-UCA-induced elevated production of IL-10 was CD4+ T cells, which were shown to be a direct target of cis-UCA action. This was also supported by the observation that production of IL-10 by stimulated splenic non-T cells or by macrophages was not altered by cis-UCA. The enhanced production of IL-10 by activated CD4+ T cells may represent a novel pathway of UVB radiation-induced, cis-UCA-mediated immunosuppression. We suggest that the elevated production of IL-10 by activated CD4+ T cells may account for the suppressor T cell phenomena described in UV-irradiated recipients.

Fas-independent death of activated CD4(+) T lymphocytes induced by CTLA-4 crosslinking

The CTLA-4 receptor is a critical inhibitory regulator of T cell proliferation and effector function. However, the mechanisms through which CTLA-4 modulates the activation of T cells remain uncertain. Initial studies, using activated human T cells, have suggested that CTLA-4 crosslinking may induce apoptosis. However, more recent experiments have demonstrated that crosslinking of the CTLA-4 receptor on the surface of resting murine T cells blocks cell cycle progression without inducing apoptosis. Here we provide evidence that CTLA-4 crosslinking on the surface of activated murine CD4(+) T lymphocytes leads to death of a substantial fraction of the cells whereas in resting CD4(+) T cells the same stimulation conditions induce cell cycle arrest without apoptosis. Cell death induced by CTLA-4 stimulation occurs independently of Fas and therefore may involve a novel pathway. CTLA-4-mediated apoptosis may be a means of terminating the function of previously stimulated T cells. Exploitation of this mechanism also may provide a therapeutic strategy to eliminate alloreactive or autoreactive T cells.

Identical genetic control of MLC reactivity to different MHC incompatibilities, independent of production of and response to IL-2

The inbred strain STS/A exhibits a higher proliferative response in the mixed lymphocyte culture (MLC) to stimulator cells of all 11 tested inbred mouse strains with 10 different major histocompatibility complex (MHC) haplotypes, as well as to stimulation with IL-2 than does the strain BALB/cHeA. However, alloantigen-stimulated BALB/c cells produce more IL-2 than STS/A cells. To study the genetic basis of these differences, we used 20 recombinant congenic strains (RCS) of the CcS/Dem series. Each of these CcS/Dem RC strains contains a different subset of about 12.5% of genes from the STS/A strain and the remaining approximately 87.5% of BALB/c origin genes. As a result the multiple non-linked genes responsible for phenotypic differences between BALB/c and STS/A became separated into different CcS/Dem strains. The strain distribution pattern (SD) of high or low MLC response of individual CcS/Dem strains to stimulator cells of four different strains was almost identical, indicating that differences in responsiveness, rather than the alloantigenic difference itself, determine the magnitude of the response, and that the responsiveness to different alloantigens is largely controlled by the same genes. The SDP of IL-2 stimulation was different from that of MLC responsiveness. The differences in the proliferative responses observed among individual CcS/Dem strains were not due to differences in numbers of CD3+, CD4+ or CD8+ cells or to the observed differences in IL-2 production, and hence they likely reflect genetically determined intrinsic properties of T cells. These results show that a set of non-linked genes controls proliferative responses in MLC irrespective of the MHC haplotype of the stimulator cells, and that stimulation with IL-2 and production of IL-2 are controlled by different subsets of genes. Since the genomes of all RCS are extensively characterized by microsatellite markers, they can be used to map the genes controlling proliferative responsiveness to stimulation with alloantigens and IL-2.

Expression and function of the costimulatory molecule B7 on murine Langerhans cells: evidence for an alternative CTLA-4 ligand

We have previously shown, through transfection experiments, that the murine B7 (mB7) molecule, a ligand for the CD28 and CTLA-4 receptors, is a sufficient costimulatory signal for the antigen-specific and major histocompatibility complex (MHC)-restricted activation of murine CD4+ T lymphocytes. In addition to mB7, another ligand with affinity for CTLA-4 has been described on spleen cells. Here we report our studies on the expression and function of these molecules on murine Langerhans cells (LC). Both anti-mB7 monoclonal antibody (mAb) 16-10A1 and human CTLA4Ig (hCTLA4Ig), a chimeric fusion protein consisting of the extracellular domain of human CLTA-4 and the constant domain of human IgG1, detected antigen(s) on cultured but not freshly isolated LC. Preincubation of cultured LC with anti-mB7 mAb did not significantly affect binding of hCTLA4Ig to these cells. This result demonstrate the existence of at least one other ligand for the CLTA-4 receptor on cultured LC. Functional studies revealed that the costimulatory activity of LC was inhibited better by hCTLA4Ig than by the anti-mB7 mAb. This differential effect was seen in the case of both alloreactive and antigen-specific, syngeneic T cell responses. These findings suggest that the non-mB7-ligand for CTLA-4 is functional and participates in the induction of immune responses by LC. Importantly, even synergistic combinations of anti-mB7 mAb and hCTLA4Ig did not inhibit completely the activity of LC. These findings therefore raise the possibility that LC express other costimulatory ligands besides mB7 and related family members.

The CD44 expressed on the earliest intrathymic precursor population functions as a thymus homing molecule but does not bind to hyaluronate

A minute population of cells representing the earliest lymphoid-restricted precursor cells in the adult mouse thymus has been isolated recently in our laboratory. This population expresses low levels of CD4, very high levels of CD44 and has a surface antigenic phenotype similar to that of bone marrow hemopoietic stem cells. To examine the role of CD44 on these cells, and to ascertain its ligand, we analysed the ability of the early thymic precursor cells to bind hyaluronate (HA) which functions as a cell adhesion molecule and a ligand for CD44. We also examined if anti-CD44 antibodies (clones IM7.8.1 and KM201) can block the thymic precursor activity. The majority of the thymic precursor cells did not show specific HA binding, indicating that HA is not the ligand for the CD44 molecules expressed on these precursor cells. HA and CD44 interactions are therefore unlikely to play a role in development of cells at this early intrathymic precursor stage. When the purified intrathymic precursor cells were incubated with anti-CD44 antibodies before intravenous transfer into recipients, very few progeny cells were detected in the thymus, although progeny were found in the spleen and lymph nodes. Coating the cells with other isotype-matched antibodies did not have this effect. However, when the same anti-CD44-coated cells were transferred directly into the recipient thymus, normal levels of progeny cells were detected in this organ. This suggests that the CD44 on the intrathymic precursor cells is a homing molecule, able to direct cells to the thymus but utilizing some ligand other than HA.

Macrophage depletion decreases IgG anti-DNA in cultures from (NZB x NZW)F1 spleen cells by eliminating the main source of IL-6

We have studied the role of macrophages in the production of IgG anti-DNA autoantibodies by (NZB x NZW)F1 mice (B/W). One of the main features of the systemic lupus erythematosus (SLE)-like disease that affects these mice, is the presence of circulating IgG autoantibodies and immune complexes, which lead to renal failure and death by the age of 8-9 months. IgG autoantibodies are produced without in vitro stimulation by total spleen cells from these mice when they reach the age of 6 months. We have demonstrated that IL-6 increases the production of IgG autoantibodies in cultures of splenic purified B cells from the old B/W mice. The aim of this study was to show the involvement of macrophages in the production of IL-6 and consequently in the production of IgG anti-DNA antibodies in vitro. We show that elimination of the macrophages by different treatments led to reduction of the content of IL-6 in the supernatants as well as of IgG anti-DNA autoantibodies. Addition of fresh, splenic or peritoneal macrophages restored the production of autoantibodies in macrophage-depleted cultures from old B/W mice. There were no differences in the capacity of IL-6 production between macrophages from old or young B/W mice, but an important difference was observed between peritoneal and splenic macrophages, where the former produced much higher levels of IL-6, and consequently were more potent inducers of IgG autoantibodies. The present results reinforce the role of macrophages and IL-6 in the production of IgG anti-DNA autoantibodies in B/W mice. The implications of these results in the pathogenesis of the disease are discussed.

Haemorrhage-induced alterations in function and cytokine production of T cells and T cell subpopulations

Haemorrhage produces alterations in macrophage, T and B cell function. In order to better define the mechanism for the effects of blood loss on immune response, we examined function of and cytokine production by purified T cells, CD4+ and CD8+ subpopulations after blood loss. Whereas T and CD4+ cells from control, unhaemorrhaged animals produced no alteration in proliferation when added to cultures of mitogen-stimulated splenocytes from normal mice, proliferation was decreased when T or CD4+ cells from haemorrhaged mice were included. The addition of CD8+ cells from haemorrhaged animals to mitogen-stimulated cultures reduced proliferation by approximately 50% more than that found when CD8+ cells from control, unhaemorrhaged animals were included. Supernatants of mitogen-stimulated splenocytes from haemorrhaged mice contained significantly less IL-2 and interferon-gamma (IFN-gamma) than did those from control, unhaemorrhaged mice. CD4+ populations from haemorrhaged mice produced significantly more IL-10, and significantly less IFN-gamma, than did CD4+ cells from control, unhaemorrhaged mice. There were no significant differences in IL-2, IL-4, IL-10 or IFN-gamma production by CD8+ cells from haemorrhaged or control mice. The present experiments demonstrate that haemorrhage affects both CD4+ and CD8+ T cell subsets. In particular, haemorrhage appeared to activate CD4+, Th2 cells, with concomitant suppression of the Th1 subpopulation. These results provide a mechanism which may contribute to the alterations in cytokine production previously described to occur following blood loss.

Effects of cyclosporin A, FK 506, and mycalamide A on the activation of murine CD4+ T cells by the murine B7 antigen

The murine B7 (mB7) protein is a potent co-stimulatory molecule for the activation of murine CD4+ T cells. We have previously shown that stable mB7-transfected Chinese hamster ovary (CHO) cells synergize with either anti-CD3 monoclonal antibodies (mAb) or concanavalin A to stimulate T cell activation. In addition, mB7 can synergize with phorbol 12-myristate 13-acetate (PMA) to induce T cell activation in an alternative pathway. In the present report we describe the effects of three immunosuppressive drugs, cyclosporin A (CsA), FK 506, and mycalamide A on mB7-mediated T cell activation. The immunophilin ligands CsA and FK 506 block activation of murine CD4+ T cells by the combination of anti-CD3 mAb and CHO-mB7 cells but do not affect activation by CHO-mB7 cells and PMA. These results support the relevance of pharmacological studies of immunosuppressive compounds in the murine model prior to their application in man. In contrast to the effects of CsA and FK 506, mycalamide A blocks activation of murine CD4+ T cells by anti-CD3 mAb and mB7 as well as activation by mB7 and PMA. On a molar basis, mycalamide A appears to be at least 10-fold more potent than FK 506 which is 100-fold more potent than CsA. Because of its effects on multiple activation pathways and because of its potency, mycalamide A could have considerable therapeutic potential.

Diverse classes of T-cell lymphomas arise in T-lymphocyte-inductive epitheliomas of the mouse salivary gland

During the course of serial transplantations of polyomavirus-induced C3H-Bittner salivary gland epitheliomas in F1-hybrid mice, three tumor sublines were found which gave rise to T-cell lymphomas of host origin. The lymphomas resembled spontaneous AKR/J thymic lymphomas in their expression of lymphoid differentiation antigens, and they may represent sequential stages in the differentiation of immature T lymphocytes. We found no evidence that polyomavirus directly induced the lymphomas, rather, the lymphomagenic events paralleled those which occur in spontaneous AKR/J thymic lymphomas.

Exclusion and inclusion of alpha and beta T cell receptor alleles

Exclusion and inclusion of T cell receptor (TCR) genes were analyzed in alpha beta TCR transgenic mice. Both transgenes are expressed unusually early on the surface of CD4-8-, HSA+, IL-2R- thymocytes. These progenitor cells give rise to progeny, which at the single-cell level contains endogenous alpha but not beta TCR-RNA as well as protein, in addition to products encoded by the transgenes. Thus, the surface expression of an alpha beta TCR does not prevent further alpha TCR rearrangement in immature thymocytes that still transcribe RAG-1 and RAG-2 genes. Reduced levels of RAG-1 and RAG-2 RNA are detectable only in CD4+8+ TCR high cells, which result from positive selection in the thymus. The results suggest that a developing T cell may try different alpha beta TCRs for binding to thymic MHC ligands, and that recombination at the alpha locus ceases only after positive selection.

Age-dependent responsiveness to interleukin-6 in B lymphocytes from a systemic lupus erythematosus-prone (NZB x NZW)F1 hybrid

The cellular mechanisms for the production of IgG anti-DNA antibodies were studied. Culture of T and B cells from old (NZB x NZW)F1 mice led to the production of IgG anti-DNA antibodies. We found that direct cell contact was partly necessary for the production of IgG anti-DNA antibodies. Fixation of the T cells showed that lymphokines were largely responsible for the antibody synthesis. Antibodies to mouse interleukin-6 (IL-6) inhibited the production of these antibodies in the T-B cell coculture. Human IL-6 could induce small "resting" B cells from the old (NZB x NZW)F1 mice to produce IgG anti-DNA antibodies in a dose-dependent fashion. The response was inhibited by an anti-human IL-6 monoclonal antibody. Large or small B cells from young (B/W)F1 mice or Balb/c mice were not induced by IL-6 to antibody production. Therefore, the capacity of the B/W mice to produce the IgG anti-DNA antibodies correlated with the ability of the B cells to respond to IL-6 and with the age at which the mice begin to have signs of the disease.

Cationization of protein antigens. VI. Effects of cationization on the immunoregulatory properties of a bovine serum albumin peptide, a.a. 506-589

Cationization of bovine serum albumin (BSA) causes a profound increase in its immunogenicity. To establish if immunoregulatory properties of an immunosuppressive peptide are affected by cationization, a BSA peptide, a.a. 506-583, was cationized and tested for its immunogenic properties. A greatly reduced amount of cationized peptide compared to native peptide was required to stimulate BSA-primed T cells to proliferate in vitro. Mice primed with the cationized peptide administered with an adjuvant responded with a significantly greater anti-BSA response than mice immunized with the native form of the peptide. In the absence of an adjuvant i.v. or i.p. administration of the native peptide was immunosuppressive, while the cationized form was immunoenhancing. Both forms of the peptide stimulated in vivo induction of L3T4+ (CD4), and Lyt-2+ (CD8) T cells. Removal of Lyt-2+ T cells from lymph node cultures following immunization with the native peptide caused a significant increase in the proliferation of the remaining T cells. This increase was not observed when the mice were immunized with the cationized peptide. No major BSA B cell determinants were present within the peptide sequence. Mice immunized with the peptide exhibited a negligible anti-BSA antibody response compared to those immunized with the whole BSA molecule. Furthermore, the peptide did not inhibit anti-BSA antibody binding to BSA. We demonstrated that cationization modifies immunoregulatory properties of an immunosuppressive BSA-derived peptide.

Polymorphism in V kappa 10 genes encoding L chains of antibodies bearing the Ars-A and A48 cross-reactive idiotypes

p-azophenylarsonate-specific antibodies of A/J mice which bear the Ars-A crossreactive idiotype utilize the V kappa-Ars-A gene segment, a member of the V kappa 10 family. Southern hybridization of genomic DNA from several inbred strains using a probe from the 5' flanking region of the V kappa-Ars-A gene demonstrated three patterns of restriction fragment length polymorphisms (RFLP). Six genes corresponding to hybridizing bands were obtained from DNA libraries of C.AKR, PERU and A/J mice, and nucleotide sequence comparisons revealed two allelic groups: AKR1 (Igk-V10.1a), AJ1 (Igk-V10.1b) and PERU1 (Igk-V10.1c); AKR2 (Igk-V10.2a), AJ2 (Igk-V10.2b), and PERU2 (Igk-V10.2c). The Igk-V10.1b gene of the A/J strain is the V kappa-Ars-A gene used in Ars-A idiotype-positive antibodies. The product of the C.AKR allele (Igk-V10.1a) contained four amino acid substitutions in CDR3 as compared with Igk-V10.1b. These substitutions probably explain the failure of AKR mice and other strains with the same V kappa 10 RFLP pattern to provide in genetic crosses a L chain which, together with the A/J VH-ArsA gene product, form Ars-A idiotype-positive antibodies. Also, the nucleotide sequence identity between the Igk-V10.1c and Igk-V10.1b alleles and the Igk-V10.2c and Igk-V10.2b alleles is significantly greater than that seen in comparisons with the Igk-V10.1a and Igk-V10.2a alleles, respectively, suggesting an evolutionary pathway similar to that of the linked Igk-J locus. BALB/c antibodies bearing the A48 regulatory idiotype contain L chains encoded by the BALB/c Igk-V10.1b and Igk-V10.2b alleles. Strongly A48 idiotype-positive antibodies utilize the Igk-V10.1b chain, and weakly A48-positive antibodies use the Igk-V10.2b L chain. The possible effects of amino acid substitutions specified by the Igk-V10.1a, Igk-V10.1c, Igk-V10.2a, and Igk-V10.2c alleles on their ability to provide L chains used in A48 idiotype-positive antibodies are discussed.

The sgp-60 molecule is linked to the plasma membrane via a glycosylphosphatidylinositol anchor

We have recently identified a novel murine glycoprotein termed sgp-60, which is expressed on the cell surface of T and B lymphocytes. Because of the profound modulatory effects of sgp-60 on activation through the T cell receptor/CD3 complex, we have examined the membrane attachment domain of the molecule. sgp-60 is not expressed on the surface of variants of a T-T hybridoma cell line that are defective in glycosylphosphatidylinositol (GPI) anchor biosynthesis. In wild-type but not in mutant cells, sgp-60 can be labeled with palmitic acid. Furthermore, the molecule can be removed from the cell surface of both T and B lymphocytes by enzymatic digestion with a phosphatidylinositol-specific phospholipase C. We conclude that the sgp-60 molecule is linked to the plasma membrane via a GPI anchor.

Peripheral selection of the T cell repertoire

T lymphocytes undergo selection events not only in the thymus, but also after they leave the thymus and reside in the periphery. Peripheral selection was found to be dependent on T cell receptor (TCR)-ligand interactions but to differ from thymic selection with regard to specificity and mechanism. Unlike thymic selection, peripheral selection required binding of antigen to the TCR, and it induced expansion of T cell clones. Tolerance to self antigens that are restricted to the periphery occurred through the elimination of self-reactive T cells and by the clonal anergy, which was associated with down-regulation of the alpha beta TCR and CD8.

Thymic selection in CD8 transgenic mice supports an instructive model for commitment to a CD4 or CD8 lineage

Immature thymocytes, which coexpress CD4 and CD8, give rise to mature CD4+CD8- and CD4-CD8+ T cells. Only those T cells that recognize self-MHC are selected to mature, a process known as positive selection. The specificity of the T cell antigen receptor (TCR) for class I or class II MHC influences the commitment to a CD4 or CD8 lineage. This may occur by a directed mechanism or by stochastic commitment followed by a selection step that allows only CD8+, class I-specific and CD4+, class II-specific cells to survive. We have generated a mouse line expressing a CD8 transgene under the control of the T cell-specific CD2 regulatory sequences. Although constitutive CD8 expression does not affect thymic selection of CD4+ cells, selection of a class I-specific TCR in the CD8 subset is substantially improved. This outcome is consistent with a model for positive selection in which selection occurs at a developmental stage in which both CD4 and CD8 are expressed, and positive selection by class I MHC generates an instructive signal that directs differentiation to a CD8 lineage.

CD4 expressed on earliest T-lineage precursor cells in the adult murine thymus

A continuous but low input of stem cells or 'prothymocytes' is necessary to maintain T-cell development in the adult thymus, but the colonizing cell has not been characterized. Precursors of T cells have been found in the minor CD4-8- population of thymocytes, but even the earliest cells of this population already have partially rearranged T-cell antigen receptor (TCR) genes. We now demonstrate that the thymus contains a minute population of lymphoid cells similar in some but not all respects to bone marrow-derived haemopoietic stem cells. This population has TCR genes in a germline state. It gives a slow but extensive reconstitution of both alpha beta and gamma delta lineages on transfer into an irradiated thymus, with kinetics indicating that it includes the earliest intrathymic precursor cells so far isolated. Surprisingly, these cells express low surface levels of the mature T-cell marker CD4.

Effector T lymphocytes present in demyelinating lesions induced by Theiler's virus

Theiler's virus causes chronic primary demyelination associated with viral persistence in SJL/J mice. We have investigated the effector functions of T lymphocytes isolated from inflammatory brain lesions to detect a local immune dysfunction associated with viral persistence. In vitro, CD4+ T cells induced B-lymphocyte proliferation and antibody secretion; CD8+ T cells had cytolytic activity. Therefore, Theiler's virus persistence does not include local immune unresponsiveness.

Transfer of T or CD8+ cells from hemorrhaged mice produce alterations in bacterial antigen specific plasma cell repertoires in normal syngeneic recipients

Hemorrhage has multiple effects on immunologic response, including alteration of B cell repertoires and T cell function. This study examined possible relationships between these two phenomena by determining the effects of T cells and T cell subsets transferred from hemorrhaged donors into normal, unhemorrhaged syngeneic recipients on B cell repertoires. Mice given total T or CD8+ cells from hemorrhaged animals then immunized with the bacterial polysaccharide antigen levan had a decreased percentage of plasma cells producing antibody to levan compared to that in mice given T or CD8+ cells from unhemorrhaged animals. These effects of post hemorrhage CD8+ cells were not seen after transfer into nu/nu mice, indicating that these cells did not directly affect B cell function, but rather required other T cell populations in order to alter the B cell repertoire. These results demonstrate that hemorrhage-induced alterations in bacterial antigen specific B cell repertoires may result from T and CD8+ cell mediated changes in T-B interactions.

Presentation of exogenous antigen with class I major histocompatibility complex molecules

Soluble antigens (Ags) in the extracellular fluids are excluded from the class I major histocompatibility complex (MHC)-restricted pathway of Ag presentation in most cells. However, an exogenous Ag can be internalized, processed, and presented in association with class I MHC molecules on specialized Ag-presenting cells (APCs). These APCs express class II molecules and can simultaneously present exogenous Ags to both class I and class II MHC-restricted T cells. These APCs may be important participants in the regulation of host immune responses. This APC activity may explain several phenomena of cytotoxic T lymphocyte (CTL) priming in vivo and might be exploited for eliciting CTL responses to protein vaccines.

Accumulation of bromodeoxyuridine-labeled cells in central and peripheral lymphoid organs: minimal estimates of production and turnover rates of mature lymphocytes

Daily lymphocyte production in both central and peripheral lymphoid organs was evaluated by associating in vivo incorporation of bromodeoxyuridine (BrdUrd) with cell surface labeling and multi-parameter flow analysis. At least 10% of mature T and B lymphocytes are generated every 24 h. The kinetic behavior of these cell populations differs, however, in that mature B cells are generated predominantly in the precursor compartments of the bone marrow, while most mature T cell generation occurs at the periphery. Therefore, peripheral expansion is the major mechanism of mature T cell production in the adult mouse. By following the accumulation of BrdUrd-labeled cells in peripheral lymphoid organs we found that the progeny of the daily lymphocyte production was sufficient to renew 30%-40% of all peripheral T and B cells every 48 h, demonstrating a high turnover rate of mature lymphocytes. We also examined the conditions of BrdUrd labeling of cycling cells in vivo. We found that while greater than 90% of bone marrow and thymus cells in S phase were labeled with a single injection of BrdUrd, in peripheral lymphoid compartments 70% of T and B cells in S failed to incorporate BrdUrd. Particular schedules of BrdUrd administration were required to overcome the low labeling efficiency of mature cells in vivo. Prolonged BrdUrd administration, however, had toxic effects on resident cells. The low labeling efficiency of BrdUrd incorporation by mature cells, as well as its potential toxicity during prolonged administration, may explain controversial results obtained by the different strategies used to study lymphocyte population dynamics.

Haemorrhage produces depressions in alloantigen-specific immune responses in the mouse through activation of suppressor T cells

The development of cell-mediated and humoral immune responses in BALB/c mice (H-2d) directed toward El4 cells (H-2b) was suppressed (cell-mediated cytotoxicity, 40-50% of control; antibody titres 127 +/- 17 versus 287 +/- 17 in controls) following haemorrhage of 30% total blood volume. This haemorrhage-induced depression of immune response can be transferred to normal recipients with T cells (3 x 10(7] from haemorrhaged syngeneic donors. Flow microfluorimetry (FMF) analysis showed no shift in CD8:CD4 ratios following haemorrhage. These results suggest that haemorrhage suppresses immune response through activation of suppressor T cells.

Proteoglycan-induced polyarthritis and spondylitis adoptively transferred to naive (nonimmunized) BALB/c mice

Mononuclear cells from BALB/c mice with progressive polyarthritis and spondylitis induced by injection of fetal human articular cartilage proteoglycan (PG) were used to transfer arthritis by intravenous injection into irradiated, nonimmunized syngeneic mice. Successful transfer of arthritis to BALB/c mice required the injection of lymphocytes from mice with arthritis, along with 50 micrograms of human fetal PG, or lymphocytes stimulated in vitro with either fetal human PG or with mouse cartilage PG. In addition, interleukin-2 or immune sera from animals with arthritis significantly reduced the time to onset of transferred disease. The onset of adoptively transferred arthritis, using cells and antigen, from the time of the first injection (38.2 +/- 18.2 days, mean +/- SD) was shortened if lymphocytes from mice with transferred arthritis were reinjected (retransferred) into other, irradiated syngeneic mice (6.1 +/- 2.6 days). The appearance of autoreactive antibodies to mouse cartilage PG in the sera of mice with adoptively transferred arthritis (secondary or tertiary) preceded the appearance of the first clinical symptoms by a few days. The transfer of arthritis was blocked by pretreatment of donor (arthritic) lymphocytes with either anti-T cell or anti-B cell antibodies and complement. Exposure of mononuclear cells from mice with arthritis to PG, and its removal prior to transfer, also resulted in transfer of the arthritis. PG-induced arthritis was not transferred to nonirradiated mice, nor to irradiated mice injected with lymphocytes from animals with primary arthritis without chondroitinase ABC-digested fetal human PG. Arthritis never developed after injection of immune sera from mice with arthritis (without cells), nor when cells of nonarthritic animals were used with chondroitinase ABC-digested fetal human PG, with or without interleukin-2.

Characterization of V beta-bearing cells in athymic (nu/nu) mice suggests an extrathymic pathway for T cell differentiation

In the present article, the expression of the T cell receptor (TcR) beta chain and other T cell molecules was evaluated in surface immunoglobulin-negative spleen cell populations of young and old BALB/c and C57BL/6 nude mice, using a panel of monoclonal antibodies. The results obtained show that in young nude mice, most Thy-1high cells do not express other T cell markers. These mice have, however, a sizable population of Thy-1low cells with the same phenotype of alpha/beta+, CD4-CD8- thymocytes or MRL/lpr peripheral T cells, expressing predominantly genes of the V beta 8 family. The evolution of alpha/beta+ cells in aging nudes is strongly suggestive of an extrathymic pathway of differentiation of these cells since (a) the acquisition of high density TcR and CD3, as well as Thy-1 or CD4CD8 antigens at the cell surface of nude V beta+ T cells is not simultaneous; (b) alpha/beta+ cells in nude mice co-express other T cell markers at random and, even in old mice, they never completely resemble to the predominant high Thy-1+ CD3+ TcR alpha/beta+, CD4+CD8+ cells of euthymic controls; and (c) BALB/c nude T cells express V beta 11 genes, that are deleted in euthymic BALB/c mice. This latter finding may also indicate differences in the mechanisms of selection of T cells specificities in the thymus vs. the peripheral pools.

Deficiency of interleukin-2 production upon addition of soluble egg antigen to cultures of isolated hepatic granulomas or hepatic granuloma cells from mice infected with Schistosoma japonicum

Schistosoma japonicum-infected C57BL/6 mice show similar dynamics of hepatic granulomatous inflammation and delayed hypersensitivity elicited by soluble egg antigens (SEA) which reach peak levels at 9 weeks of infection and then spontaneously regress. In an attempt to link the level of interleukin 2 (IL-2) production to the spontaneous regression of hepatic granulomatous inflammation, the study determined the dynamics of IL-2 production by SEA-challenged isolated hepatic granulomas (HG) and cells isolated enzymatically from the HG. The production of IL-2 by SEA-stimulated HG or HG cells reached its peak when these preparations from 9-week-infected mice were stimulated and fell thereafter. Some possible mechanisms that might explain the IL-2 deficiency were examined. This deficiency is not due to the in vitro binding of IL-2 by the HG cells of infected mice and is, therefore, due rather to underproduction of IL-2. The deficiency was also not explained by reduced numbers of antigen-presenting cells (macrophages or B cells) or of L3T4+ T lymphocytes. In vitro SEA-induced IL-2 production by HG cells from acutely infected mice was suppressed consistently by Lyt-2+ T cells from the spleens and in the majority of our experiments by Lyt-2+ T cells from the HG of mice infected for 10 weeks. These findings are consistent with the main features of our working hypothesis, but it remains to be proven that in vivo deficiency of lymphokine(s) such as IL-2 is responsible for the spontaneous decrease in granulomatous inflammation and that this lymphokine deficiency is a result of suppression.

Plasticity of T-cell function. II. Transient induction of CD8 (Ly-2) expression in cloned EL-4 lymphoma cells depending on cell density

EL-4 lymphoma cells are able to suppress the primary humoral immune response of spleen cells to sheep erythrocytes or 4-hydroxy-3-iodo-5-nitrophenylacetyl-keyhole limpet haemocyanin (NIP-KLH) in vitro. Typically, the cells suppress very efficiently in small numbers, but lose this capacity as the numbers increase. Three clones were analysed and this fluctuation in function was paralleled by a fluctuation in the expression of CD8 (Ly-2). Clones were incubated for 2 days, starting from different seeding concentrations, and analysed with cytofluorography. Neither Thy-1 nor CD5 (Ly-1), H-2 K, H-2 D, LFA-1 (all positive) nor CD4 (L3T4) or MEL-14 (both negative) were influenced by this treatment. In contrast, cells were CD8- at high seeding concentrations, and CD8+ at low seeding concentrations. When cell cultures grew to higher densities, the cells again lost the capacity to express CD8. Experiments testing the suppressive capacity of individual EL-4 clones after preculture at different densities or in the presence of antibodies against CD8 suggest that the efficiency of suppression may well be correlated to the amount of CD8 expressed.

Interleukin 2 receptor expression and interleukin 2 production in exponentially growing T cells: major differences between in vivo and in vitro proliferating T lymphocytes

In the present study we have assessed the growth requirements for in vivo proliferating mature T cells. For that purpose we have selected experimental approaches which allow the study of exponential growth in vivo of a major fraction of T cells, and make it possible to obtain large numbers of T cells in cycle. Two types of growing T cell populations were used: peripheral T lymphocytes, proliferating exponentially after transfer into syngeneic athymic nude mice, and activated T cells in lymph nodes of normal mice draining the site of oxazolone administration. The results obtained show that mature T cell growth in vivo is not accompanied by expression of high-affinity interleukin 2 (IL2) receptor in the majority of activated cells, is not abrogated by in vivo administration of anti-IL2 receptor antibodies or enhanced by the in vivo injection of recombinant IL2, and that in vivo growing T cells do not produce detectable amounts of IL2, as evaluated functionally by limiting dilution assays or the presence of IL2 mRNA, detected by Northern blots or in situ hybridization. The presented data thus indicate that the rules known to apply to T cell activation and proliferation in vitro differ from those used by in vivo growing T lymphocytes, at least in the two systems studied.

Structural and evolutionary comparisons of four alleles of the mouse Igk-J locus which encodes immunoglobulin kappa light chain joining (J kappa) segments

The Igk-J locus of the mouse encodes the immunoglobulin kappa light chain joining (J) segments. Four Igk-J alleles have been described on the basis of restriction enzyme length polymorphisms. The nucleotide sequences of the Igk-Ja allele (type strain, C.C58), Igk-Jc allele (type strain, SJL/J), and Igk-Jd allele (type strain, SK/CamRk) have been determined and are compared with the previously reported Igk-Jb allele sequence (type strain, BALB/c). The mouse sequences are also compared with published sequences for rat and human J kappa sequences. Far more differences were found between the Igk-Ja allele and the other mouse alleles than between any two of the latter. These result in two amino acid substitutions which distinguish the J2 and J3' segments of the Igk-Ja allele from the other three alleles. Use of the Phylogenetic Analysis Using Parsimony program to generate a phylogenetic tree strongly indicates that after divergence from the rat ancestor, there appears to have been an early split between the Igk-Ja allele and the evolutionary precursor of the other mouse alleles. There also appears to have been far less divergence from the ancestral condition in the Igk-Ja allele than in the other alleles. Also, the presence of only one convergent mutation among the four mouse alleles provides strong evidence against any crossing over within the Igk-J locus during the history of these alleles. Finally, the differences in rates of evolution of the Igk-J alleles are in marked contrast to the relatively uniform rates of divergence of four alleles of a mouse V kappa gene, Igk-VSer.

Peripheral T lymphocytes: expansion potential and homeostatic regulation of pool sizes and CD4/CD8 ratios in vivo

Peripheral T lymphocytes are self-renewable cell populations since, when transferred into syngeneic T cell-deficient athymic mice, they expand in the absence of exogenous antigen stimulation. Quantification of the expansion potential of CD4+ cells by transfer of the same population into successive host mice shows that these cells are able to divide up to 56 times in vivo. Therefore, as a population, CD4+ cells can increase in size 8 x 10(5)-fold, an expansion potential of similar magnitude to that previously reported for colony-forming units. Injection of different numbers of T cells at different CD4/CD8 ratios is followed by T cell accumulation to a similar plateau in recipient nude mice. This indicates that peripheral T lymphocytes are tightly regulated by homeostatic mechanisms that control pool sizes and CD4/CD8 ratios, in a manner independent of the cell input into the peripheral compartment. This kinetic behavior of mature T cells permits the maintenance at the periphery of any T cell specificity previously selected in the thymus. The expansion capacity of peripheral T cells may also allow extensive modulation of peripheral T cell specificities, which would confer a major role to post-thymic selection of mature peripheral T cell repertoires.

L3T4+ T cells promoting susceptibility to murine cutaneous leishmaniasis express the surface marker Ly-24 (Pgp-1)

In a murine model of cutaneous leishmaniasis, the importance of T cell-dependent immunity has been documented by the susceptibility to parasite infection of athymic nude mice of both genetically resistant and genetically susceptible strains. T lymphocytes from uninfected mice have the capacity to promote resistance to Leishmania major infection in nude recipients, whereas T cells from mice chronically infected with L. major not only fail to mediate protection, but totally abrogate the host-protective effect of normal mouse lymphocytes. Both these effects are mediated by T cells which have the phenotype L3T4+Ly-2-. To discriminate between the two activities, we have tried to separate the L3T4+ population on the basis of additional cell surface markers and we have found that peripheral L3T4+ lymphocytes could be subdivided according to their expression of the Ly-24 (Pgp-1) surface marker. In adoptive transfer experiments, both the Ly-24+ and the Ly-24- subset of L3T4+ cells from uninfected mice had the capacity to mediate resistance to infection with L. major. However, disease-promoting activity was only found in the L3T4+Ly-24+ and not in the L3T4+Ly-24- subset of cells from mice with chronic cutaneous disease. Moreover, Ly-24 expression was strongly increased in lymphocytes from chronically infected mice and in vitro limiting dilution analysis confirmed that the vast majority of L. major-reactive T cells was L3T4+Ly-24+. In genetically susceptible mice with chronic cutaneous leishmaniasis, Ly-24 therefore appears to be a marker for lymphocytes with the capacity to abrogate resistance to disease, these cells being activated and expanding in the course of progressive L. major infection. Ly-24 expression is a useful tool for phenotypic identification and selective enrichment of antigen-activated and possibly memory T cells. It may facilitate the isolation of L. major-specific T cell clones with defined activities.

Expression of Ly-6A/E alloantigens in thymocyte and T-lymphocyte subsets: variability related to the Ly-6a and Ly-6b haplotypes

We have studied the cellular basis for differential expression of the Ly-6A/E alloantigen on T cells obtained from mice of the Ly-6a (10-20% Ly-6A/E+) and Ly-6b (50-60% Ly-6A/E+) haplotypes. During T-cell ontogeny only a small fraction (less than 12%) of thymocytes expressed Ly-6A/E. By 4 weeks of age adult levels of Ly-6A/E bearing lymphocytes were seen in peripheral lymphoid tissue. Immunohistochemical studies of the thymus revealed that Ly-6A/E+ cells were located predominantly in the medulla with small clusters of Ly-6A/E+ cells throughout the cortex. Consistent with this result, phenotypic studies showed that in the adult thymus the majority of Ly-6A/E expression was on mature CD4+CD8- and CD4-CD8+ cortisone-resistant and precursor CD4-CD8- thymocytes. However, a much higher percentage of CD4+CD8- and CD4-CD8- thymocytes as well as CD4+CD8- peripheral T cells expressed Ly-6A/E from Ly-6b mice. Furthermore, although gamma interferon induced increased Ly-6A/E expression in certain thymocyte and T-cell subsets, this induction functioned preferentially for cells obtained from Ly-6b mice. Studies using F1 hybrid mice (Ly-6a x Ly-6b) indicated that the "basal" level of Ly-6A/E expression on these subsets appeared to be under codominant genetic control, whereas gamma interferon-induced regulation of Ly-6A/E expression appeared to be under dominant genetic control. Collectively, these results suggest that the expression of Ly-6A/E on a particular T-cell subset is established in the thymus and is a stable characteristic of each haplotype. In addition, the low levels of Ly-6A/E expression for the Ly-6a haplotype appear to be partially due to the inability of the majority of resting CD4+ T cells to express Ly-6A/E and to the relatively poor induction of this protein by gamma interferon.

Structural and evolutionary comparisons of four alleles of the mouse immunoglobulin kappa chain gene, Igk-VSer

The mouse Igk-VSer gene encodes an immunoglobulin kappa light chain variable region which gives rise to two phenotypic polymorphisms of mouse kappa chains. The nucleotide sequences of coding and flanking regions of the Igk-VSerc and Igk-VSerd alleles found in recently inbred strains of wild mice are compared with those of the Igk-VSera and Igk-VSerb alleles described previously. Results suggest that the gene is evolving randomly and that framework 2 and complementarity determining region 2 are preserved, presumably for overall light chain structure. Results indicate that all four alleles have an octamer motif upstream of the gene which should be functional and allow prediction of whether or not the product of the germ line gene will be detectable as either the IB-peptide or Ef1a phenotypic polymorphism. Southern hybridization of genomic DNA using as probe a 1-kb Xba I-Xba I fragment located approximately 4 kb upstream of the BALB/c Igk-VSerb coding region demonstrated the presence of homologous DNA in mice bearing the Igk-VSera allele and absence from mice bearing the Igk-VSerc and Igk-VSerd alleles. Nucleotide sequence comparison of BALB/c and SK/CamRk (Igk-VSerd) DNA in this region demonstrated that BALB/c contained an insertion 2.4 kb in length which was absent from SK/CamRk. Both strains contain DNA homologous to the reverse complement of the mouse Bam5 repetitive element at the point of the insertion, with BALB/c containing approximately 70 nucleotides more of the element than SK/CamRk. Surprisingly, the strains containing DNA related to the Xba I-Xba I probe are not those determined to be the most similar by nucleotide sequence comparisons and by the Phylogenetic Analysis Using Parsimony program. The evolutionary relationship of the alleles and a possible basis for the inconsistency presented by the Xba I-Xba I fragment-related DNA are discussed.

Demethylated CD8 gene in CD4+ T cells suggests that CD4+ cells develop from CD8+ precursors

Mature T cells and medullary thymocytes bear either the CD4 or CD8 differentiation antigen. Precursor cells in the thymus express neither CD4 nor CD8 (CD4-8-), but most cortical thymocytes are CD4+8+. Whether CD4+ and CD8+ mature T cells arise directly from CD4-8- precursors or from a CD4+8+ intermediate remains unresolved. In this study, methylation of the CD8 gene in murine T cells and thymocytes was examined. There was progressive demethylation of the CD8 gene in the thymus during the transition from CD4-8- to CD4+8+. A similar pattern of demethylation of the CD8 gene was seen in CD4+ mature T cells, suggesting previous expression of CD8 in the CD4+ lineage.

Nucleotide sequence analysis of the C.AKR Lyt-2a gene: structural polymorphism in alleles encoding the Lyt-2.1 T-cell surface alloantigen

The Lyt-2a allele of the C.AKR strain of mice (genotype Lyt-2a, Lyt-3a) was cloned, and its complete nucleotide sequence as well as that of 2 kb of 5' flanking DNA was determined. The sequence was compared with the partial sequence of the Lyt-2a allele of DBA/2 (genotype Lyt-2a, Lyt-3b) and the nearly complete sequence of the B10.CAS2 Lyt-2b allele reported by Liaw and coworkers (1986). The coding regions of the two Lyt-2a alleles differ from each other by two nucleotide substitutions in the three exons over which they could be compared, resulting in two amino acid substitutions in the leader and transmembrane segments. The coding region of the C.AKR Lyt-2a allele differs from the Lyt-2b allele by two nucleotide substitutions in the extracellular V-like domain, one of which is silent and the second of which leads to substitution of valine for methionine at amino acid position 78 giving rise to the Lyt-2.1 allotypic specificity. The coding region of the DBA/2 Lyt-2a allele shares with C.AKR the allotypic substitution at position 78 and differs from Lyt-2b by three additional nucleotide substitutions in the coding regions, two of which lead to amino acid substitutions in the leader and transmembrane segments. It would therefore appear that the Lyt-2 alleles of the three strains analyzed are distinct, and the nomenclature Lyt-2a1 and Lyt-2a2 is suggested to distinguish the alleles of C.AKR and DBA/2, respectively. These alleles share a common difference from the Lyt-2b gene product at position 78, and since the amino acid substitutions which distinguish them from each other are in the leader and transmembrane segments, their mature Lyt-2 gene products appear antigenically identical.

Structure and expression of the Lyt-3a gene of C.AKR mice

The mouse Lyt-3a gene, which encodes the Lyt-3.1 T-cell surface alloantigen of the C.AKR strain, has been cloned, and the nucleotide sequence of its exons and more than 2 kb of 5' flanking sequence have been determined. The gene extends over approximately 16 kb of DNA and consists of six exons encoding leader, leader plus V-like domain, membrane-proximal, transmembrane, and cytoplasmic domains. The only difference between the coding region of the Lyt-3a gene and the cDNA sequences reported for Lyt-3b (Nakauchi et al. 1987. Panaccio et al. 1987) is at position 77 of the mature protein where Lyt-3a encodes serine and Lyt-3b encodes arginine. This substitution must therefore be the basis for the serological distinction between the Lyt-3.1 and Lyt-3.2 alloantigens. Potential TATA and CAAT sequences, two Sp1 protein binding sites, two extended repeats of the dinucleotide, CA, a number of short inverted repeats, and an inverted segment of the mouse B1 repetitive sequence are found 5' to the Lyt-3a gene. Two consensus poly-A addition signals and a complete copy of the mouse B1 sequence are found 3' to the gene. Both B1-related regions are flanked by short direct repeats suggesting that they arose by an insertional mechanism. Cotransfection of the Lyt-3a gene together with a cloned Lyt-2a gene resulted in expression of both Lyt-2 and Lyt-3.1 on the surface of Ltk- and BW5147 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Mapping of Igk-V genes using backcrossed laboratory and wild mice

In the mouse, the genes coding for the Ly-2 antigen, the beta chain of the T-cell receptor, and the immunoglobulin kappa light chain have been located on chromosome 6. Although a tentative order has been proposed for these genes, very few data have been reported concerning their genetic distance. To address this question, we have produced backcross mice between SJL and MAI (a wild-derived strain belonging to the Mus musculus), since these mice segregate for the Ly-2 and Igk-C proteins and for the Igk-V24, Igk-V21, Igk-V10, Igk-V8, and Igk-V4 genes. Twelve recombinants were obtained from 163 backcross mice studied. Two mice showed a recombination between the (Igk-V24, Igk-V10, Igk-V8, Igk-V4) and the (Ly-2, Igk-C, Igk-V21) groups, and ten mice displayed a recombination between the (Igk-V24, Igk-V10, Igk-V8, Igk-V4) group and the Tcrb-C loci. These data imply the following gene order: Tcrb-C .... (Igk-V24, Igk-V10, Igk-V8, Igk-V4) .... (Igk-V21, Igk-C, Ly-2). They indicate a distance of 6.1 cM between Tcrb-C and (Igk-V24, Igk-V10, Igk-V8, Igk-V4) and 1.2 cM between Igk-V24, Igk-V10, Igk-V8, Igk-V4 and the (Igk-V21, Igk-C, Ly-2) groups.

T-cell-specific deletion of T-cell receptor transgenes allows functional rearrangement of endogenous alpha- and beta-genes

In B cells the loci encoding immunoglobulin chains usually show allelic exclusion; a given B cell transcribes and translates only one productively rearranged allele of the heavy and light chain loci. This ensures that each B cell expresses only one antigen receptor. The loci encoding T-cell receptor (TCR) alpha- and beta-genes may behave similarly. We have previously reported that the expression of a transgenic TCR beta-chain prevents functional and nonfunctional V beta rearrangements in the endogenous beta-chain loci but not D beta J beta rearrangements. We have also been unable to detect the expression of the TCR gamma-chain locus in thymocytes of these mice (unpublished observations). To study the mechanisms involved in forming a mature T-cell repertoire further, we have constructed mice expressing alpha- and beta-TCR transgenes derived from a cytotoxic T-cell clone that is specific for the male antigen H-Y in the context of H-2Db MHC molecules. Here we show that in these mice rearrangement of endogenous alpha-chain loci is also suppressed, although to a lesser extent than rearrangement of beta-chain loci. In addition, in male alpha beta TCR transgenic mice we observed T-cell clones which had deleted both transgenic alpha- and beta-chain genes and expressed endogenous alpha- and beta-chain TCR genes. These cells are presumably derived from rare thymocytes that leave the male thymus because their TCR no longer recognizes self antigen. The vast majority of CD4+8+ nonmature thymocytes expressing alpha- and beta-transgenes are deleted in the male thymus.

Deficiency of interleukin-2 activity upon addition of soluble egg antigen to cultures of spleen cells from mice infected with Schistosoma japonicum

Schistosoma japonicum-infected C57BL/6 mice show similar dynamics of hepatic granulomatous inflammation (HGI) and delayed hypersensitivity (DH) elicited by soluble egg antigens (SEA) which reach peak levels at 9 weeks of infection and then spontaneously regress. The in vitro SEA-induced proliferation of spleen cells (SC) from infected animals attained its high point and then declined when SC from 5-week-infected mice were used. The present study determined the dynamics of interleukin-2 (IL-2) production by SEA-challenged SC from infected mice in an attempt to link the level of IL-2 production to the spontaneous regression of the aforementioned T-cell-mediated immune responses. The production of IL-2 by SEA-stimulated SC reached its peak when cells from 7-week-infected mice were challenged at least 2 weeks after the peak of the proliferative response, but declined at about the same time as the HGI and DH responses. Therefore, the decline in IL-2 activity cannot alone explain the diminished proliferative response but could account for the reduction in HGI and DH in vivo. Some possible mechanisms that might explain the IL-2 deficiency were examined. This deficiency is not due to the in vitro binding of IL-2 by the SC of infected mice and is, therefore, likely to be due to underproduction of IL-2. Nor is the deficiency explained by reduced numbers of antigen-presenting cells (macrophages and B cells) or of L3T4+ T lymphocytes or by suppression of IL-2 production by macrophages or macrophage products such as prostaglandins. However, suppression of IL-2 production was observed consistently upon coculture of SC from acutely infected mice with SC from mice infected for 10 weeks. The cells which suppress appear to be Lyt2+ T cells. The data are consistent with the hypothesis that suppressor T cells inhibit the production of IL-2 and perhaps of other cytokines or lymphokines and that this suppression explains the spontaneous down-regulation of HGI which occurs during schistosomiasis japonica.